Index
Andromeda's Screens Filter Help Index

Welcome to the help system for the Andromeda's Screens Filter. Scroll down to see  more help topics. Click the mouse on green text to jump to descriptions for  each topic.

Help Topic Categories

General Information

Buttons

Blend Controls

Variation Windows

Enhance Image Controls

Mezzo Controls

Pattern Controls

Output Controls


Blend Controls

Blend

A combination of a Mezzotint and a Pattern  produced by taking a weighted average of the two Pixel  values. See Mezzo+Pattern Blend (Mezzoblend).

Difference

A combination of a Mezzotint and a Pattern  produced by subtracting one Pixel value from  the other. See Mezzo+Pattern Difference.

Mezzo

Selecting Mezzo in the Select Screen box changes  the type to Mezzotint. In the Mezzo box, a drop-down  menu gives a choice of four Mezzo types: Uniform Mezzo,  Mezzo XY Growth, Radial Growth A, and Radial  Growth B.

Mezzo+Pattern Blend (Mezzoblend)

Selecting Mezzo+Pattern Blend in the Select Screen  box changes the type to a Blend, or weighted  average of a Mezzotint and a Pattern.

The Pattern Blend % slider appears, which controls how  much Pattern and how much Mezzo will be used  in the Blend: 0% is all Mezzo, 50% is half  and half, and 100% is all Pattern.

Both the Mezzo Type and the Pattern Type must  be chosen, and the "Show controls for:" buttons allow  the user to set each one. To preview just the Mezzo  or just the Pattern, select the Mezzo or Pattern  buttons, and then reselect Mezzo+Pattern Blend when done  previewing. You can also temporarily set the Pattern Blend  % to 0 to see just the Mezzo, or 100 to see just  the Pattern, and then set it back when done previewing.

Mezzo+Pattern Difference

Selecting Mezzo+Pattern Difference in the Select  Screen box changes the type to a Difference of  a Mezzotint and a Pattern.

Both the Mezzo Type and the Pattern Type must  be chosen, and the "Show controls for:" buttons allow  the user to set each one. To preview just the Mezzo or  just the Pattern, select the Mezzo or Pattern  buttons, and then reselect Mezzo+Pattern Difference when  done previewing.

Select Screen

This box contains the controls for selecting the general  screen type.

Show Controls for

For Mezzo+Pattern Blend and Mezzo+Pattern  Difference, this allows the user to select whether to set  the parameters for the Mezzo part of the Blend, or the  Pattern part.


Buttons

Cancel

Clicking on the Cancel button quits the Screens Filter  and returns to the Host Application without doing anything  to the image. Only settings that were explicitly saved in Novice  Mode are saved, otherwise the current settings are lost.

Defaults

Clicking on the Defaults button opens up the Defaults  dialog, and gives a choice of setting all parameters to their  default values, or just a group of settings. This is a quick way  of getting back to reasonable values if you have been experimenting  with unusual settings.

Expert

Click this button from Novice Mode to enter  Expert Mode.

Help

Clicking on the Help button starts up the on-line Help  mechanism, which displays most of the information on Expert  Mode found in the manual. Selecting a category at the top  displays information about that category on the bottom.

While Help is active, all buttons and controls in the main filter  dialog are disabled, including the Cancel button. You  must click "Done" to get out of Help before doing anything else.

Novice

Click this button from Expert Mode to enter  Novice Mode.

OK

Clicking on the OK button saves the current settings  and begins to apply them to the high resolution image stored in  the Host Application. A progress bar appears to indicate  the current status of the screening operation. The time it will  take depends on the image size, the memory configuration, and  the computer speed. The user may abort by clicking on the "Cancel"  button next to the progress bar (or typing Command-Period on the  Macintosh, Escape on the PC). The settings will be saved (to the  Prefs file) even if the rendering is cancelled after clicking  OK.

The "current settings" saved by clicking OK are used in two ways:  (1) they are the initial settings the next time the Screens Filter  is run (even if the Host Application is restarted),  and (2) if the Screens Filter is applied to an image without running  the user interface, these are the settings used.

In Photoshopª, after the Screens Filter has been applied the first  time, the user interface can be bypassed with the "Last Filter"  command at the top of the Filter menu (or by typing Command-F  on the Macintosh, Control-F on the PC). To force the user interface  to appear, hold the option key down on the Macintosh, or the Alt  key on the PC while doing the "Last Filter" command.

After the Screens filter is done rendering the image, the user  can use the "Undo" and "Redo" commands (Command-Z on the Mac,  Control-Z on the PC), to toggle between the unscreened and screened  images. Also, the "Revert" command will return you to the original  image (as saved on disk).


Enhance Image Controls

Amount

This slider controls the amount of Sharpening.  For Unsharp Masking, the default is set to 350 for fairly  dramatic sharpening. For Neighborhood Enhancement  the default is set to 100. Please see Unsharp Masking  or Neighborhood Enhancement for more details.  Range: -500 to 1000.

Blurring

An Enhancement which defocuses an image.

Enhance

To improve the quality of an image by increasing (or  decreasing) its sharpness.

Enhanced Photo

Clicking this button in either the Left Window or  Right Window column allows previews of the Unsharp  Masking or Neighborhood Enhancement applied to  the Input Photo before screening. If Enhance Photo  is not checked, Enhancement is turned off and  the Enhanced Photo preview will be identical to the  Input Photo preview.

Enhance Photo

The Enhance Photo box allows selection of the Enhancement  or "sharpening" of the original Input Image by  one of two methods: Unsharp Masking or Neighborhood  Sharpening. Either process can be used to sharpen or blur  the input photo by an amount corresponding to the Amount slider  value. Enhancement can be turned off to eliminate this  step in the screening process (as in Standard Mezzotint Screening)  by unchecking Enhance Photo.

When using Mezzo, Pattern, Blend or  Difference screening, a crisper, sharper detailed screened  image will be output because the Filter will as a default enhance  the Input Photo. As a default, the Enhance Photo  box is checked and the corresponding specified sharpening parameters  are automatically applied to the Input Image before  subsequent screening.

Andromeda terminology for sharpened mezzotints is Mezzograms.  You may turn off Enhance Photo to screen your gray scale  photo to a traditional (standard) mezzotint.

To observe the comparative differences between the original photo  and the enhanced photo, click on Input Photo in the  Left Window column, and Enhanced Photo in  the Right Window column. Please note that previews (and  rendering) with Unsharp Masking Radius set to a high  value (>15) are slower.

Neighborhood Enhancement

This sharpening method is offered as an alternative  to Unsharp Masking, which is normally used. Only the  Amount is adjustable; the Radius is always  one  Pixel. It is a simpler, faster method, and will give  good results for many images.

The default Amount is 100. Using high or negative values  produce similar Artistic Effects as using these values  in Unsharp Masking.

Radius

Unsharp Masking sharpens by taking each Pixel in  the image, examining the Pixels surrounding it, and  modifying its value (according to the values of the Pixels  close by). The Radius slider controls the size of this  neighborhood. Increasing the Radius means that the program will  examine a larger area when sharpening each Pixel. A  larger Radius also causes the program to run slower, and may cause  unwanted artifacts to appear in images with features or details  which are smaller than the Radius.

For most images, dividing the resolution by 60 gives a good value  for Radius. For example, 5 pixels is adequate for a 300 dpi image.

Another method for setting the Radius is to examine an area where  two different colors or definite shades of gray meet. There will  be a fuzzy transition area of "inbetween" shades. The radius can  be set according to the width (in pixels) of this area, although  some experimentation will be necessary to get the best value.  Range: 1 to 100 (pixels).

Sharpening

An Enhancement which makes an image appear  in sharper focus.

Unsharp Masking

In spite of its name, this is a sharpening  procedure. (The name is an industry standard and is a bit misleading.)  It is used to make edges in the Input Photo appear sharper,  or more in focus, before any Screen is applied. Its  operation is somewhat similar to Neighborhood Sharpening,  but is more powerful, having an adjustable Radius parameter,  and a weighted rather than uniform average over the neighboring  Pixels. Unsharp Masking in this filter is similar to  Unsharp Masking operations in other image manipulation programs  such as Photoshopª.

Different values of the Amount slider produce different  effects, as follows:

Amount Slider	Effect

less than -100	Haloing or ghosting (special effect)

-100	Pure blur

-99 to -1	Combination of blur and original

0	Original, unmodified

1 to 100	Combination of sharpening and original,  original weighted more

greater than +100	Combination of sharpening and original, sharpening  weighted more.


General Information

Variations of any slider value in Expert Mode can be  done in the Variation Windows by clicking on the specific  slider name. When the slider has been selected in this manner,  a short underline appears under the slider name to show it has  been selected. Also, the name of the selected slider and its current  value appear above the Fine-Coarse slider at the top  of the Variation Windows.

For example, if the Variation Windows are currently  being used to adjust Threshold, and its current value  is 128, you will see "Threshold: 128" displayed in the  bar above the boxes. You will also see a short underline under  the name "Threshold" adjacent to the Threshold slider.  Suppose you wish the Variation Windows to adjust Unsharp  Masking Amount instead. Click the word "Amount"  in the Enhance Photo box, and you will notice it then  becomes underlined. If its current value is 500, you will see  "Amount: 500" appear above the Fine-Coarse  slider at the top of the Variation Windows.

Holding down the Command key on the Mac (Control key on the PC)  and pressing the mouse button allows you to move the square in  the Preview Windows which selects the area displayed  in the Variation Windows.

Due to memory constraints, sometimes it is not possible to make  the full resolution source image available in the Preview Windows  of the Screens filter. This is especially true  of large images. You will notice under the Threshold  slider in Expert Mode it will say either (Full resolution  preview) or (Preview sampled down by 2:1), or some higher ratio.  This means that when zooming in the Preview Windows,  you will see less detail than in the Host Application  if the image has been sampled down. This does not affect the final  output, only the previews. Once you have clicked OK,  the image will be rendered in full detail.

Artistic Effects

This refers to settings that are chosen to produce a  certain "look" rather than accurate reproduction of the original  Input Image. This is the more creative side of the Screens  Filter.

Bitmap

This term is used to mean a Binary, 1-bit  per Pixel image, where each Pixel is either  on or off (black or white). Technically, there can be Grayscale  or color bitmaps, but that is not how we are using this  term in our manual.

Binary

This term is used to mean a 1-bit per Pixel image,  where each Pixel is either on or off (black or white).  In this manual, Binary is interchangeable with Bitmap,  although technically the two terms mean different things.

CMYK

A four color image consisting of Cyan, Magenta, Yellow  and Black layers. ("K" is used for Black so as not to be confused  with Blue from RGB.) Each layer is usually an 8-bit grayscale,  so each pixel requires 32 bits (4 bytes) of storage.

A color image must be converted to CMYK before printing. Images  are normally scanned and displayed on the computer screen in RGB.  The RGB->CMYK conversion may be done by the Host  Application (before or after applying the Screens Filter),  or it may be done later by some other program, or by the printer  driver.

CMYK colors are subtractive, and are printed on white paper. Although  any color (including black) can be produced by the three primary  pigments: Cyan, Magenta, and Yellow, the fourth black layer is  used to produce better quality (black text looks much better when  printed with black ink than a combination of CMY inks.)

The four layers are printed at four different screen angles to  avoid Moire Effects.

Constrain File Size

A checkbox in the Photoshopª Image Size dialog.  If you want to increase resolution of your image by reducing its  size then check this box. Your image will not be resampled. If  you want to resample your image to a lower or higher Image  Resolution before running the Screens Filter, uncheck this  box.

Dot

A spot on a printed page or in a Bitmap, where  the size and shape determines the darkness or Grayscale  at that point in the image. If the dot is printed in black on  a white background, then the larger the dot, the darker that spot  in the image will be. Dots are usually arranged in regular patterns  on the page, and the density is measured in Dots/Inch.  For a Bitmap, the dot size should be at least four times  larger than the resolution of the Bitmap, to reduce  Posterization.

Dots/Inch

Number of Pattern Dots/Inch measured along  either axis (tilted by Pattern Angle). Range: 1 to 300.

Expert Mode

A dialog in the Screens Filter which allows the user  to individually set each parameter by moving sliders or typing  in values, and previewing the different steps in the screening  process. Expert Mode is entered from Novice Mode by  pressing the Expert button.

Grayscale

A Grayscale image is a continuous tone (contone) black  and white image consisting of Pixels which can be any  shade of gray. Although each Pixel can be anywhere from  2 bits to 16 bits, normally each Pixel is 8 bits (one  byte), or 256 shades of gray. This is represented by the numbers  0 to 255, where 0 is black, 128 is 50% gray, and 255 is white.  Sometimes percentages are used instead, where 0% is black and  100% is white. (You may see other programs or manuals where the  numbers are reversed: 0 is white and 255 or 100% is black, but  this is rare.)

Halftone

A given spot on a page of a printed document either  has ink or no ink; printing does not deal directly in shades of  gray. Photographs or other material containing gray shades must  therefore be converted to spots of pure black or pure white.

The usual method of doing this is called halftoning. A halftoned  photograph consists of a regular grid of dots also called a screen.  The screen or grid is made fine enough so that individual dots  are inconspicuous to the eye. Typical halftone grids are from  85 Dots/Inch to 133 Dots/Inch. The number  of Dots/Inch (also called Lines/Inch) is called  the screen value.

Halftones simulate gray values by making use of limitations in  the eye's resolution. Even though the eye will not see individual  dots in the halftone, it will perceive their average brightness,  or gray value, over a small area. If a particular small area in  the original photo has pixel value of 230 (of a possible 255),  it is 90% white and 10% black. It would be represented in the  halftone as a series of small black dots, each occupying 10% of  its grid cell, the rest of the grid cell being white. Because  of its limited resolution, or ability to see fine details, the  eye sees only the overall brightness of this small area, which  is 90%.

If another area in the photo is 90% black, the halftone would  be a white spot occupying 10% of its grid cell, the rest of the  cell being white. If another area in the photo is 50% black, its  halftone representation would be half black and half white in  each cell. Magnified, this appears as a checkerboard, but to the  eye, it just looks 50% white.

Halftones have been in use for many years and the technology is  highly developed. Andromeda's Screens Filter provides an alternative  to conventional halftoning by using randomized mezzo worm  patterns as the dot shape, with variations in screen value, screen  angle, and spot shape.

Halftone Dot

A Dot in a Halftone image.

Host Application

The program that launched the Screens Filter. It must  be able to run Photoshopª compatible plug-in modules. Examples  of Host Applications are: Photoshop, Debabelizer, Jag II, Premiere,  Photopaint, Fractal Painter, Matisse, etc. (All names are trademarks  of their respective companies.)

Image Resolution

This refers to the resolution, or dpi (dots per inch)  of the Input Image from the Host Application.  (This is not to be confused with the Dots/Inch of  a dot pattern generated by the Screens Filter, which is the Screen  Resolution.)

Image Size

This term refers either to the size in bytes of the  Input Image, or the height and width of the Input  Image. For gray scale, the size in bytes is the height  in Pixels times the width in Pixels. For RGB  color images the size in bytes is the height times the  width times three; for CMYK color it is the height times  the width times four.

If the image is compressed, it will take up less space on disk  than the image size. When calculating memory usage, you must use  the image size in bytes, not the size of the file on disk.

Input Image

The grayscale or color image received from  the Host Application when the Filter is started. If  part of the image in the Host Application is selected  when the filter is started, that selection becomes the Input Image.

Input Photo

Selecting this option for the Left Window or  Right Window causes the original Input Image to  be previewed. This is always what is displayed in the Left  Window in Novice Mode.

Left Window

The large Preview Window in the upper left  part of the Novice Mode and Expert Mode dialog.  In Novice Mode the Input Photo is always displayed,  and in Expert Mode, the display is selectable.

Mix

The process by which the screen and enhanced photo are  combined to make the output photo. In the mix, each pixel is a  linear combination of the corresponding Pixels in the  screen and the enhanced photo.

The Screens Filter creates a Grayscale image and blends  it with the Input Photo to create the final Output  Image. This created image is called the Screen.  The Screen can consist of a Mezzotint, a Pattern,  or a mix of the two.

Moire Effect

Pronounced moray, an undesired interference pattern  produced by superimposing two repetitive patterns. In the Screens  Filter, we try to avoid Moire Effects between the Screen pattern  and the underlying Pixel structure of the Input Image,  and also between the Pattern and the Mezzo when  doing Blends. Moire Effects can be avoided by using  Corrected instead of Uncorrected Pattern Types,  and also by making sure that the Input Image is of high  enough resolution.

When printing color images, the four CMYK layers are  printed at four different angles chosen carefully to avoid Moire  Effects, e.g. Cyan: 15 deg, Magenta: 75 deg, Yellow: 0 deg, Black  45 deg.

Novice Mode

A dialog in the Screens Filter which allows the user  to easily choose settings from factory-installed or user-defined  Presets. This is the initial dialog displayed when entering  the Screens Filter. Novice Mode is entered from Expert Mode  by pressing the Novice button.

Pixel

A "picture element", the basic unit or "spot" in an  image. In a computer, each pixel is represented by anywhere from  1 to 64 bits. Normally, a bitmap (binary)  image is one bit per pixel, a Grayscale is 8 bits (1  byte), an RGB is 24 bits (3 bytes), and a CMYK is  32 bits (4 bytes).

Pixels may also be represented by Indexed Color, where each pixel  is usually represented by 8 bits, and each of the 256 possible  values refers to a color in a Color Lookup Table.

The Screens Filter only works with Grayscale, RGB,  and CMYK.

Pixels/Inch

In this manual, this term is used to refer to the Input  Resolution, or the dpi (dots per inch) of the Input  Image from the Host Application.

Posterization

The effect on a Grayscale or color image when  a limited number of shades of gray or colors are used to represent  the image.

For example, if you take a continuous tone Grayscale image  represented by 256 shades of gray and force the value of each  Pixel to be a multiple of 10, the image will now only  have 26 shades of gray instead of 256. The image will therefore  look "posterized", that is there will be patches of distinct shades  rather than smooth, gradual transitions.

Posterization is usually undesirable, although some artists produce  this effect intentionally. To avoid it when using the Screens  Filter (or any Halftone Dot generating process), make  sure your Input Resolution is at least four times higher  than your Screen Resolution. The higher this ratio,  the more shades of gray will be available, since there will be  more Pixels per Screen Dot, and therefore  a greater number of possible Dot sizes.

Preset

A named group of parameter settings. The sliders are  set in Expert Mode and then named and saved in Novice  Mode.

Preview Windows

The two large image display windows in both Novice  Mode and Expert Mode, referred to as  the Left  Window and the Right Window. In Expert Mode,  each window may be used to display any of the four steps in the  Screening process.

The Preview Windows may be independently zoomed and panned, or  they may have identical magnifications and positions if the Sync  button is checked.

The square displayed inside both windows shows the current position  of the view in the Variations Windows. This square can  be moved by holding down the Command key on the Mac (Control key  on the PC) and dragging the box. Otherwise clicking the mouse  over the Preview Windows zooms in, and Option-clicking zooms out  on the Mac (Alt-clicking zooms out on the PC). Clicking the small  square on the bottom right (which displays the zoom level) does  a fit-in-window.

Resolution

The number of Pixels/Inch of an image. Higher  resolution means better quality, but it also means more computer  resources and processing time are required. If an image  is less than about 300 dpi (dots per inch), it is considered low  resolution. Most desktop printers and scanners are 300 dpi or  higher, and magazine quality is 1000 dpi or higher. Computer monitors  are generally in the ranger of 60-100 dpi, but by zooming in an  application program, portions of images can be magnified to see  the same detail that high resolution printers can use.

You need to be concerned about resolution when using the Screens  Filter, to make sure that the Image Resolution is high  enough to produce quality output. Your printer resolution should  be at least as high as your Image Resolution, and your  Image Resolution should be at least four times higher  than your Screen Resolution.

RGB

A three color image consisting of Red, Green and Blue  layers. Each layer is usually an 8-bit Grayscale, so  each Pixel requires 24 bits (3 bytes) of storage.

A color image must be converted to CMYK before printing.  Images are normally scanned and displayed on the computer screen  in RGB. The RGB->CMYK conversion may be done by the  Host Application (before or after applying the Screens  Filter), or it may be done later by some other program, or by  the printer driver.

RGB colors are additive; any color (including white) can be produced  by the three primary colors: Red, Green, and Blue. RGB is easier  to work with than CMYK for the graphic artist, and requires  less storage.

Right Window

The large Preview Window in the upper middle  part of the Novice Mode and Expert Mode dialog.  In Novice Mode the Output Image is always  displayed, and in Expert Mode, the display is selectable.

Screen

A Mezzotint, Pattern, or a combination  of the two using Blend or Difference.

Screening

The process of generating or applying a Screen.

Screening Resolution

This term refers to the Worms/Inch, Dots/Inch  or Lines/Inch used to generate the Screen  in the Screens Filter. It does not have anything  to do with your computer screen! The Screening Resolution should  be at least four times lower than the Image Resolution for  good quality output.

Sync

If checked, all zoom and pan operations done to one  of the Preview Windows is also done to the other, so  that both Window A and Window B have the same  view. If not checked, the two Preview Windows can be  zoomed and panned independently.

Zoom In/Out

Clicking the mouse over the Preview Windows  zooms in, and Option-clicking zooms out on the Mac (Alt-clicking  zooms out on the PC). To see the screened output image, it is  best to zoom in at 1:1 (see lower right corner of each window  for magnification status ":3" indicates "1:3", "1:" indicates  "1:1" and so on). Clicking on the small square on the bottom right  does a fit-in-window.


Mezzo Controls

Mezzogram

This is an Andromeda coined term for crisp Mezzotints,  ideal for product advertising where detail is necessary. A Mezzogram  screen is a Mezzotint screen applied to a sharpened  gray scale image (see also Enhance Photo & Mezzotint).

Mezzotint

Mezzotinting is an alternative to halftoning as  a way to simulate gray values with a fine pattern of pure black  and white. A mezzotinted photo consists of small, irregular shapes,  rather than a regular grid of Dots. In light areas the  mezzotint looks like small black shapes on a white background;  dark areas have small white shapes on a black background. When  viewed close up, the shapes look slightly like chromosomes or  worms. Mezzotints, like Halftones, have screen  values, which are given in terms of "Worms/Inch" in  Series 3 Screens.

Mezzotinting is used more for special effects than for maximum  photographic accuracy in reproduction. Frequently mezzotinting  will be done at a Worms/Inch figure where the individual  shapes can be perceived, giving a deliberately grainy or impressionistic  effect, which can be somewhat mysterious looking. Mezzotinting  is sometimes used in conjunction with deliberate blurring of the  photo, and occasionally in conjunction with exaggerated sharpening.  The Andromeda Screens Filter provides blurring and sharpening  capability.

Mezzo Type

There are five types of Mezzotints in the  Screens filter. The Uniform Mezzo type corresponds to  standard Mezzotints made by photographic means. The  others provide special effects which are not available using photographic  methods.

Each type is controlled by several sliders. For all mezzotint  types except Uniform Mezzo, the sliders belong to one  of two groups, denoted A Controls and B Controls.

Mezzo XY Growth

This screen is characterized by Worms that  grow in size as they move away from the X and Y axes. The Mezzotint  grows so that near the X axis, the stretched Worms  are more or less aligned with the X axis, and similarly for Y.

Uniform Mezzo

This is the traditional true Mezzotint Screen.  The "wormy" pattern is the same as that achieved by the traditional  high quality photographic screening process.

Worms

This term refers to the small, irregular shapes which  make up the Mezzotints produced by the Screens Filter.

Worms/Inch

This setting determines how fine the Worm pattern  is.  A Mezzotint of a given value of Worms/Inch corresponds  roughly in fineness of detail to a halftone screen of equal Dots/Inch.

It is highly recommended that the Worms/Inch slider value be less  than or equal to 25% of the dpi value of the original Input  Photo, to produce good quality output. Range: 1-100.

X Offset

Increasing this setting will move the entire Worm  pattern to the left, and decreasing will move to the right.  Range: 0 to 100.

X Origin

For 'Growth' Mezzotints, the Worms/Inch  slider determines how many Worms/Inch there are  at the origin. As you get farther from the origin, the Worms  are bigger. The origin can be anywhere within the bounds  of the photo. For X origin = 0, the origin is at the left edge;  for 100, it is at the right edge. Range: 0 to 100 (% of pic width).

Y Offset

Increasing this setting will move the entire Worm  pattern upward, and decreasing will move downward. Range:  0 to 100.

Y Origin

For Y=0, the origin is at the top edge of the pattern;  for 100, it is at the bottom edge. Range: 0 to 100 (% of pic height).


Output Controls

Output Image

This is the final image prepared by the Filter and returned  to the Host Application. This final image can be the  Enhanced Photo by itself, the Screen by itself,  a Mix of the two, or the Mix with a Threshold  applied.

Output Image (Screen/Photo Mix)

The box containing controls which combine the Screen  and the Enhanced Image to produce the Output  Image.

Screen %

This slider controls output contrast. Less screen percent  shows more image and less screen (higher contrast), and more screen  percent shows more screen and less image (lower contrast). 100%  produces an output image with just screen, and no original image.  0% produces an output image with just enhanced image, and no screening.  Normally, values around 50% are used. Range: 0 to 100.

Special Mezzo

This checkbox only appears when the Input Image is  CMYK color, and Uniform Mezzo is being used.  Checking Special Mezzo causes the Black layer to have its Worms/Inch  doubled (the Cyan, Magenta, and Yellow layers are unaffected).  Doing this improves the output quality for some images.

Threshold

Threshold is a general term for converting a Grayscale  value into a black or white value by comparing it with  a cutoff number. For example, if the cutoff is 128, all Grayscale  values in the range of 0-128 are turned black and all values in  the range of 129-255 are turned white.

Threshold is also the name of the checkbox in the Screens filter  which turns this conversion on or off, and the name of the slider  controlling the cutoff value if conversion is on.

The Threshold checkbox must be checked to have the Screens Filter  produce output consisting of black or white pixels, rather than  shades of gray. You may uncheck Threshold to produce continuous  tone grayscale output, if you wish to Threshold it later in the  Host Application, or have some other requirement for  Grayscale output.

If Threshold is checked, the Threshold slider sets the Threshold  level, or cutoff.


Pattern Controls

# Spokes

This slider sets the number of spokes for the Spokes  Pattern Type.

# Waves

For wavy ellipses, the perimeter of each ellipse goes  in and out a number of times set by this slider. If # waves is  0, the ellipses are smooth. Range: 0 to 100.

A Controls

If more than three sliders are required for a particular  Mezzo or Pattern Type, they are divided into  two sections: A Controls and B Controls. Clicking  on one or the other makes all the sliders available to the user.

Angle

Tilts entire Pattern; positive angles are  counterclockwise, negative angles are clockwise, 0 degrees is  horizontal. Uncorrected Patterns use precise angles,

Corrected Patterns round the angle selected by the user  to the nearest integer ratio, which is within 2 degrees of the  desired angle. Range: -90 to +90 degrees.

Asymmetry

Controls the shape of Corrected Dots. See  Corrected Dots-xxx for the specific effect. Range -100  to 100.

B Controls

If more than three sliders are required for a particular  Mezzo or Pattern Type, they are divided into  two sections: A Controls and B Controls. Clicking  on one or the other makes all the sliders available to the user.

Center X

This sets the position of the center of Ellipses  and Spokes along the photo's X (horizontal) axis.  If 0, the center is on the photo's left edge; if 100, the center  is on the right edge. Range: 0 to 100 (% of photo width).

Center Y

This sets the position of the center of Ellipses  and Spokes along the photo's Y (vertical) axis.  If 0, the center is on the photo's top edge; if 100, the center  is on the bottom edge. Range: 0 to 100 (% of photo height).

Corrected

Before one of the first six Patterns is used  in a Screen, it goes through a process which adjusts  the Grayscale distribution in each pattern cell. This  adjustment improves the rendition of Grayscale tones  during the Screening process, and minimizes Posterizing.  A further important property of each Corrected Pattern is  that all cells in the entire Pattern are absolutely  identical. This requirement avoids Moire Effects.

Because of these two special properties, Corrected Patterns  perform better than the others when used alone, as opposed  to in a Blend, for Screening.

Corrected Dots-Cross

White squares or rectangles on a black background. Cross  and Square dots can give impression of superior sharpness in some  circumstances. If the Asymmetry control is 0, crosses  are square, else rectangular. If positive, long axis of rectangle  is parallel to pattern axis, else perpendicular to it.

Corrected Dots-Diamond

Squares to diamonds to wavy lines. Similar to ellipses  but always having sharp corners.  If the Asymmetry control  is 0, square checkerboard pattern, else stretched squares. If  positive, long axis of diamond is parallel to pattern axis, else  perpendicular to it.

Corrected Dots-Elliptical

At 50% black, squares or diamonds, depending on Asymmetry.  At high or low black, dots become circular or oval. High positive  Asymmetry: line-like shapes, parallel to main pattern  axis. At high negative, perpendicular to main axis.

Corrected Dots-Round

Standard halftone dots, going from small round dots  at high or low black, tending to a square checkerboard near 50%  black if Asymmetry is 0. At values near 50, black dots  touch at smaller angles along thin tendrils, intended to compensate  for midrange dot gain. At negative values, black dots touch more  suddenly, which may give a 'crisper' impression.

Corrected Dots-Square

Black squares or rectangles on a white background. The  exact inverse of the Cross dot. If the Asymmetry control  is 0, crosses are square, else rectangular. If positive, long  axis of rectangle is parallel to pattern axis, else perpendicular  to it.

Corrected Lines

These are straight line patterns. For asymmetry 0, each  side of line has same profile. For asymmetry not zero, one side  of line has a sharper profile than other, useful for certain effects  where a visible sharp line edge is desired.

Curvature

If zero, the Spokes radiate straight out from  the center. If positive, Spokes become spirals moving  clockwise as you go out from the center. If negative, the spirals  move counterclockwise as you get farther from the center. The  amount of curvature also depends on the number of Spokes.  Range: -300 to 300 (worms/inch).

Dots-Circular

An Uncorrected Pattern Type consisting of  a grid of circular dots. The area between the center of each dot  and the Inner Radius is pure black. The area between  the Inner Radius and the Outer Radius varies  from black to white, and the area outside the Outer Radius  is pure white. If the Outer Radius is less than  or equal to the Inner Radius, the dots are pure black  with sharp edges, and the Inner Radius is used for the  size.

Dots-Round/Square

An Uncorrected Pattern Type consisting of  a grid of dots similar to Halftone dots. With an average  density of 50%, they have smooth transitions between black and  white.

Ellipses-Smooth

An Uncorrected Pattern Type consisting of  concentric circles or ellipses. Setting the Stretch  to zero gives circles, and setting it to a non-zero value produces  ellipses of a given eccentricity. The Angle setting  will tilt the ellipses, and has no effect on circles.

The center of the ellipses can be placed anywhere in the image  with the Center X and Center Y sliders, the  number of ellipses is determined by the Lines/Inch slider,  and the Line Width may also be adjusted.

Ellipses-Wavy

This Pattern Type is the same as Ellipses-Smooth  except that the circles or ellipses are wavy (sine waves).  The waviness is controlled by the Wave Height: setting  it to 0 eliminates the waves, and increasing its value accentuates  the waves. The # Waves sets how many waves are in each  ellipse.

Ellipses-Wavy & Sharp

This Pattern Type is the same as Ellipses-Wavy  except that the waves are sharp (triangular waves) instead  of being smooth (sine waves).

Growth Rate

If 0, the growth rate is low, so that the Worms get  bigger slowly farther from the origin. If 100, the growth rate  is high.

(for XY Growth): The Mezzotint grows so that  near the X axis, the stretched Worms are more or less  aligned with the X axis, and similarly for Y.

(for Radial Growth A): The Mezzotint grows  so that the stretched Worms 'point' toward and away  from the origin; that is, they are stretched radially. Range:  0 to 100.

Inner Radius

Sets the size of the inside of the dot. Circular Dots  are solid black from their center to the Inner Radius. From the  Inner Radius to the Outer Radius, the dot  density drops from solid black to solid white. Outside of the  Outer Radius, the dot cell is pure white. The Outer  Radius is constrained to be equal to or larger than the  Inner Radius. Range 0-100 (% of dot cell size).

Lines

A type of Pattern generated by the Screens  Filter consisting of lines (rather than Dots or Worms).  The lines may be straight, wavy, or elliptical.

Lines/Inch

This slider sets the number of Lines in each  inch, traveling perpendicular to the family of Lines.  The Lines/Inch is the screen value. Range: 1 to 300.

Lines-Straight

An Uncorrected Pattern Type consisting of  parallel straight Lines.

Lines-Wavy

This Pattern Type is the same as Lines-Straight  except that the Lines are wavy (sine waves).  The waviness is controlled by the Wave Height: setting  it to 0 eliminates the waves, and increasing its value accentuates  the waves. The Wave Length controls many waves are in  each line.

Lines-Wavy & Sharp

This Pattern Type is the same as Lines-Wavy  except that the waves are sharp (triangular waves) instead  of being smooth (sine waves).

Line Width

This slider sets the relative widths of the black and  white portions of each Line, as seen in line profile  or cross-section. At 50%, the Line profile goes straight  from black to white and back down. If less than 50%, the black  part of the Line is wider; if more than 50%, the white  portion predominates. Range: 0 to 100 (% of line space).

Outer Radius

Sets the size of the outside of the dot. Circular Dots  are solid black from their center to the Inner Radius.  From the Inner Radius to the Outer Radius, the dot density  drops from solid black to solid white. Outside of the Outer Radius,  the dot cell is pure white. The Outer Radius is constrained to  be equal to or larger than the Inner Radius. Range 0-100  (% of dot cell size).

Pattern

Selecting Pattern in the Select Screen box  changes the type to Pattern. In the Pattern box, a drop-down menu  gives a choice of fifteen Pattern types.

The Screens Filter can create a large number of geometric or algorithmic  patterns. Some possibilities are: arrays of dots of several kinds;  arrays of straight or wavy lines; families of concentric circles  or ellipses, either smooth or wavy; and spokes or spirals. The  waves in the lines and ellipses can be sinusoidal or sharp.

Pattern Blend %

This slider controls how much Pattern and how much Mezzo  will be used in a Mezzo+Pattern Blend: 0% is all Mezzo,  50% is half and half, and 100% is all Pattern.

Pattern Type

There are fifteen types of Patterns in the  Screens Filter.  Each type is controlled by several sliders. There  are six Corrected Patterns, and nine Uncorrected  Patterns. Corrected Patterns minimize Posterizing  and Moire effects, and perform better than the  others when used alone, as opposed to in a Blend. Uncorrected  Patterns have more variety and more range in their parameter  settings, and are most useful in Blends with Mezzos  or for creating Artistic Effects.

Radial Growth A

This screen is characterized by Worms that  grow in size as they move away from the center.  The Mezzotint  grows so that the stretched Worms 'point' toward  and away from the origin; that is, they are stretched radially.  There is a slider to control the Growth Rate.

Radial Growth B

This screen is characterized by Worms that  grow in size as they move away from the center, in a stretch pattern  controlled by the Stretch Factor slider.

Spokes

This Pattern Type consists of lines radiating  outward from the center, where the lines get thicker as the go  outward.

The center of the pattern can be placed anywhere in the image  with the Center X and Center Y sliders, the  number of spokes is determined by the # Spokes slider,  and the Line Width may also be adjusted. A Curvature  of 0 yields straight spokes, and non-zero values curve  the spokes.

Stretch

For ellipses, setting the Stretch to zero gives circles,  and setting it to a non-zero value produces ellipses of a given  eccentricity. Positive values of Stretch elongate the ellipses  on the X-axis, negative values on the Y-axis. The ellipses can  also be rotated with the Angle Slider.

Stretch Factor

(for Radial Growth B): If the setting is less  than 50, the Worms are stretched tangentially. If the  setting is more than 50, the Worms are stretched radially.  If equal to 50, the individual Worms are not stretched,  but the overall pattern expands linearly with increasing distance  from the origin. Range: 0-100.

Uncorrected

Uncorrected patterns do not have the optimum Grayscale  distribution in each pattern cell, or necessarily have  identical pattern cells. Therefore they will not generally give  as good Grayscale renditions, and may introduce Moire  and Posterizing effects when used as Screens.  They are useful because they have more variety and more range  in their parameter settings. They are most useful in Blends  with Mezzotints, and may not make a satisfactory  Screen when used alone. They can be used for many interesting  special effects.

Wave Controls

Allows user to set wave characteristics for wavy patterns.

Wave Height

This slider sets the height in Pixels of each  wave, from topmost peak to bottommost peak. If 0, the Lines  or Ellipses are smooth. For more positive values,  the waves are larger. If Stretch is nonzero, the waves  are stretched. Range: 0-400 (pixels).

Wave Length

This slider sets the distance in Pixels from  the peak of one wave to the peak of the next, measuring parallel  to the Lines. Range: 0 to 500 (pixels).


Variation Windows

Coarse

Moving the slider over the Variation Windows to  the right causes the increments to be more Coarse, meaning that  there will be a greater difference, or step size, between the  Current and the More parameter setting, and  between the Current and the Less.

Current

The Variation Window showing a mini-preview  of the Current setting of the parameter being varied.

Holding down the Command key on the Mac (Control key on the PC)  and pressing the mouse button allows you to move the square in  the Preview Windows which selects the area displayed  in the Variation Windows.

Fine

Moving the slider over the Variation Windows to  the left causes the increments to be more Fine, meaning that there  will be a lesser difference, or step size, between the Current  and the More parameter setting, and between the  Current and the Less.

Less

The Variation Window showing a mini-preview  of the Less setting of the parameter being varied.

Holding down the Command key on the Mac (Control key on the PC)  and pressing the mouse button allows you to move the square in  the Preview Windows which selects the area displayed  in the Variation Windows.

More

The Variation Window showing a mini-preview  of the More setting of the parameter being varied.

Holding down the Command key on the Mac (Control key on the PC)  and pressing the mouse button allows you to move the square in  the Preview Windows which selects the area displayed  in the Variation Windows.

Original

The Variation Window showing a mini-preview  of the original Input Image at the location selected  by the movable square in the Preview Windows.

Holding down the Command key on the Mac (Control key on the PC)  and pressing the mouse button allows you to move the square in  the Preview Windows which selects the area displayed  in the Variation Windows.

Variation Windows

Variations of any slider value in Expert Mode can  be done in the Variation Windows by clicking on the specific slider  name. When the slider has been selected in this manner, a short  underline appears under the slider name to show it has been selected.  Also, the name of the selected slider and its current value appear  above the fine-course slider at the top of the Variation Window.

Clicking on the More Window increases the selected slider's  value; clicking on the Less Window decreases it. The  amount of increase or decrease is controlled by the Fine-Coarse  slider above the Variation Windows.

Holding down the Command key on the Mac (Control key on the PC)  and pressing the mouse button allows you to move the square in  the Preview Windows which selects the area displayed  in the Variation Windows.