Table of Contents

1. Images

PostScript provides powerful capabilities for including and manipulating raster images. Understanding image handling is essential for documents containing photographs, scanned content, and bitmap graphics.

1.1. Overview

PostScript image capabilities include:

  • Bitmap images - Grayscale and color raster images

  • Image transformations - Scaling, rotating, and skewing

  • Color models - RGB, CMYK, and indexed color

  • Compression - Various encoding schemes

  • Masking - Transparency and clipping with images

  • Sampling - Resolution and interpolation

Images in PostScript are defined by:

  • Dimensions - Width and height in pixels

  • Bit depth - Bits per sample (1, 2, 4, 8, 12)

  • Color space - Gray, RGB, CMYK, etc.

  • Data source - Inline or procedural

1.2. Basic Image Syntax

1.2.1. The image Operator

Basic grayscale image:

% image: width height bits/sample matrix datasource image

% Simple 8x8 grayscale image
8 8                      % Width, height
8                        % 8 bits per sample
[8 0 0 -8 0 8]          % Transformation matrix
{<FF 00 FF 00 FF 00 FF 00
  00 FF 00 FF 00 FF 00 FF
  FF 00 FF 00 FF 00 FF 00
  00 FF 00 FF 00 FF 00 FF
  FF 00 FF 00 FF 00 FF 00
  00 FF 00 FF 00 FF 00 FF
  FF 00 FF 00 FF 00 FF 00
  00 FF 00 FF 00 FF 00 FF>}
image

1.2.2. Image Transformation Matrix

The matrix transforms image space to user space:

% [a b c d tx ty]
% For standard image (top-down):
% [width 0 0 -height 0 height]

% Example: 100x100 pixel image
100 100 8
[100 0 0 -100 0 100]  % Standard orientation
{<...data...>}
image

1.2.3. Image Data Source

Data can be provided in several ways:

% 1. Hexadecimal string
{<FFFF0000>}

% 2. Procedure returning strings
{
  currentfile 10 string readhexstring
  pop
}

% 3. File or filter
imageFile

% 4. Inline data
currentfile /ASCII85Decode filter

1.3. Color Images

1.3.1. RGB Images (colorimage) 

% colorimage: width height bits/sample matrix
%              datasource ncolors multiproc colorimage

% RGB image (3 components)
4 4                      % 4x4 pixels
8                        % 8 bits per sample
[4 0 0 -4 0 4]          % Matrix
{<FF0000 00FF00 0000FF FFFFFF
  000000 FF00FF FFFF00 00FFFF
  808080 FF8000 80FF00 8000FF
  C0C0C0 404040 F0F0F0 0F0F0F>}
false                    % Single data source
3                        % 3 color components
colorimage

Multiple data sources:

% Separate R, G, B sources
4 4 8
[4 0 0 -4 0 4]
{<FF 00 00 FF>}  % Red channel
{<00 FF 00 FF>}  % Green channel
{<00 00 FF FF>}  % Blue channel
true             % Multiple sources
3
colorimage

1.3.2. CMYK Images 

% CMYK: 4 color components
4 4 8
[4 0 0 -4 0 4]
{<data...>}
false
4                % 4 components (C,M,Y,K)
colorimage

1.4. Image Positioning and Scaling

1.4.1. Positioning Images

Use coordinate transformations:

gsave
  % Position at (100, 100)
  100 100 translate

  % Scale to 200x150 points
  200 150 scale

  % Draw 1x1 unit image
  % (will be scaled to 200x150)
  1 1 8
  [1 0 0 -1 0 1]
  {<...data...>}
  image
grestore

1.4.2. Fitting Image to Area 

/fitImage {  % imgWidth imgHeight areaWidth areaHeight -> -
  4 dict begin
    /areaH exch def
    /areaW exch def
    /imgH exch def
    /imgW exch def

    % Calculate scale (maintain aspect ratio)
    /scaleX areaW imgW div def
    /scaleY areaH imgH div def
    /scale scaleX scaleY lt { scaleX } { scaleY } ifelse def

    % Center in area
    /offsetX areaW imgW scale mul sub 2 div def
    /offsetY areaH imgH scale mul sub 2 div def

    gsave
      offsetX offsetY translate
      imgW scale mul imgH scale mul scale

      % Draw image here
      % 1 1 8 [1 0 0 -1 0 1] {...} image
    grestore
  end
} def

1.4.3. Tiling Images 

/tileImage {  % imgProc tileW tileH -> -
  3 dict begin
    /h exch def
    /w exch def
    /img exch def

    0 h 500 {
      /y exch def
      0 w 500 {
        /x exch def
        gsave
          x y translate
          img exec
        grestore
      } for
    } for
  end
} def

1.5. Image Data Formats

1.5.1. ASCII Hexadecimal

Most portable format:

% Each byte as two hex digits
8 8 8
[8 0 0 -8 0 8]
{<
  00 10 20 30 40 50 60 70
  80 90 A0 B0 C0 D0 E0 F0
  % ... more data
>}
image

1.5.2. ASCII85 Encoding

More compact ASCII representation:

8 8 8
[8 0 0 -8 0 8]
currentfile /ASCII85Decode filter
image

% ASCII85 encoded data follows
Ascii85EncodedDataHere~>

1.5.3. Binary Data

Most compact (not always portable):

% Binary data (if interpreter supports it)
8 8 8
[8 0 0 -8 0 8]
currentfile /ASCIIHexDecode filter
image

% Hex data
0001020304050607...

1.6. Image Masking

1.6.1. Image Mask (1-bit transparency) 

% imagemask: width height polarity matrix datasource imagemask

% Create mask (1 bit per pixel)
8 8
true                     % true = 1 bits are painted
[8 0 0 -8 0 8]
{<81 42 24 18 18 24 42 81>}  % Checkerboard mask
imagemask

Using mask with color:

gsave
  1 0 0 setrgbcolor  % Red

  % Mask determines which pixels are painted
  8 8 true
  [8 0 0 -8 0 8]
  {<FF 00 FF 00 FF 00 FF 00>}
  imagemask
grestore

1.6.2. Masked Image

Image with transparency mask:

% Draw background
0.9 0.9 0.9 setrgbcolor
0 0 100 100 rectfill

% Draw masked image
<<
  /ImageType 1
  /Width 8
  /Height 8
  /ImageMatrix [8 0 0 -8 0 8]
  /BitsPerComponent 8
  /Decode [0 1]
  /DataSource {<FF808080404020201010080804040202>}
  /Mask {<81422418182442 81>}
>> image

1.7. Practical Image Examples

1.7.1. Example 1: Gradient Image 

/gradientImage {  % width height -> -
  2 dict begin
    /h exch def
    /w exch def

    w h 8
    [w 0 0 h neg 0 h]
    {
      % Generate gradient data
      0 1 w 1 sub {
        /x exch def
        x w div 255 mul cvi
        1 string dup 0 4 -1 roll put
      } for
    }
    image
  end
} def

% Usage
gsave
  100 100 translate
  200 100 scale
  1 1 gradientImage
grestore

1.7.2. Example 2: Checkerboard Pattern 

/checkerImage {  % size -> -
  1 dict begin
    /size exch def

    size size 1
    [size 0 0 size neg 0 size]
    {
      % Generate checkerboard
      0 1 size 1 sub {
        /y exch def
        0 1 size 1 sub {
          /x exch def
          x y add 2 mod 0 eq { <FF> } { <00> } ifelse
        } for
      } for
    }
    image
  end
} def

gsave
  100 100 translate
  100 100 scale
  8 checkerImage
grestore

1.7.3. Example 3: QR Code Style Pattern 

/qrPattern {  % size -> -
  1 dict begin
    /s exch def

    s s 1
    [s 0 0 s neg 0 s]
    {
      % Generate random pattern
      0 1 s 1 sub {
        pop
        0 1 s 1 sub {
          pop
          rand 2147483647 div 0.5 gt { <FF> } { <00> } ifelse
        } for
      } for
    }
    image
  end
} def

gsave
  100 100 translate
  100 100 scale
  32 qrPattern
grestore

1.7.4. Example 4: Image Border 

/framedImage {  % imageProc borderWidth -> -
  2 dict begin
    /border exch def
    /img exch def

    gsave
      % Draw border
      0 setgray
      border neg dup moveto
      border 2 mul 0 rlineto
      0 border 2 mul rlineto
      border -2 mul 0 rlineto
      closepath
      2 setlinewidth
      stroke

      % Draw image
      img exec
    grestore
  end
} def

% Usage
{
  1 1 8
  [1 0 0 -1 0 1]
  {<...data...>}
  image
} 5 framedImage

1.8. Image Filters and Effects

1.8.1. Invert Image 

/invertImage {  % imgProc -> -
  gsave
    % Invert by using XOR-like effect
    1 setgray
    0 0 1 1 rectfill

    % Subtract mode (simulated)
    % Draw image
    exec
  grestore
} def

1.8.2. Grayscale Conversion 

% For RGB image, convert to grayscale
/rgb2gray {  % r g b -> gray
  0.299 mul     % Red weight
  exch 0.587 mul add  % Green weight
  exch 0.114 mul add  % Blue weight
} def

1.8.3. Brightness Adjustment 

/brightenImage {  % imgProc amount -> -
  2 dict begin
    /bright exch def
    /img exch def

    gsave
      % Adjust brightness
      1 bright add dup dup setrgbcolor

      % Multiply mode (simulated)
      img exec
    grestore
  end
} def

1.8.4. Threshold Effect 

/thresholdImage {  % threshold -> -
  1 dict begin
    /thresh exch def

    8 8 1  % 1 bit per pixel
    [8 0 0 -8 0 8]
    {
      % Read original data, apply threshold
      currentfile 8 string readhexstring pop
      {
        thresh gt { 1 } { 0 } ifelse
      } forall
    }
    image
  end
} def

1.9. Image Optimization

1.9.1. Downsampling 

/downsampleImage {  % factor -> -
  1 dict begin
    /factor exch def

    % Original: 800x600
    % Factor: 2
    % Result: 400x300

    800 factor div cvi
    600 factor div cvi
    8
    [800 factor div 0 0 600 factor div neg 0 600 factor div]
    {
      % Sample every nth pixel
      % (simplified - real downsampling is more complex)
    }
    image
  end
} def

1.9.2. Image Compression 

% Using filters for compression

% RLE (Run-Length Encoding)
<<
  /ImageType 1
  /Width 100
  /Height 100
  /BitsPerComponent 8
  /Decode [0 1]
  /ImageMatrix [100 0 0 -100 0 100]
  /DataSource currentfile /RunLengthDecode filter
>> image
% RLE data here

% LZW Compression
<<
  /ImageType 1
  /Width 100
  /Height 100
  /BitsPerComponent 8
  /Decode [0 1]
  /ImageMatrix [100 0 0 -100 0 100]
  /DataSource currentfile /LZWDecode filter
>> image
% LZW data here

1.10. Working with Image Dictionaries

1.10.1. Image Dictionary Format 

<<
  /ImageType 1              % Type of image
  /Width 100                % Width in pixels
  /Height 100               % Height in pixels
  /ImageMatrix [100 0 0 -100 0 100]  % Transform
  /BitsPerComponent 8       % Bits per sample
  /Decode [0 1]            % Decode array
  /DataSource currentfile   % Data source
  /Interpolate false        % Interpolation
>> image

1.10.2. Color Image Dictionary 

<<
  /ImageType 1
  /Width 50
  /Height 50
  /ImageMatrix [50 0 0 -50 0 50]
  /BitsPerComponent 8
  /Decode [0 1 0 1 0 1]    % RGB decode ranges
  /DataSource currentfile
  /Interpolate true         % Smooth scaling
>> false 3 colorimage

1.11. Image Data Generation

1.11.1. Procedural Images 

/proceduralImage {
  100 100 8
  [100 0 0 -100 0 100]
  {
    % Generate image data procedurally
    0 1 99 {
      /y exch def
      0 1 99 {
        /x exch def

        % Calculate pixel value
        x y add 2 mod 255 mul
        1 string dup 0 4 -1 roll put
      } for
    } for
  }
  image
} def

1.11.2. Noise Image 

/noiseImage {  % width height -> -
  2 dict begin
    /h exch def
    /w exch def

    w h 8
    [w 0 0 h neg 0 h]
    {
      % Random noise
      0 1 w h mul 1 sub {
        pop
        rand 255 mul 2147483647 div cvi
        1 string dup 0 4 -1 roll put
      } for
    }
    image
  end
} def

50 50 noiseImage

1.11.3. Plasma Effect 

/plasmaImage {  % width height -> -
  2 dict begin
    /h exch def
    /w exch def

    w h 8
    [w 0 0 h neg 0 h]
    {
      0 1 h 1 sub {
        /y exch def
        0 1 w 1 sub {
          /x exch def

          % Plasma calculation
          x w div 360 mul sin
          y h div 360 mul sin add
          2 div 1 add 127.5 mul cvi
          1 string dup 0 4 -1 roll put
        } for
      } for
    }
    image
  end
} def

1.12. Image Transformations

1.12.1. Mirrored Image 

/mirrorImage {  % imageProc direction -> -
  % direction: 0=horizontal, 1=vertical
  2 dict begin
    /dir exch def
    /img exch def

    gsave
      dir 0 eq {
        % Horizontal mirror
        -1 1 scale
        -1 0 translate
      } {
        % Vertical mirror
        1 -1 scale
        0 -1 translate
      } ifelse

      img exec
    grestore
  end
} def

1.12.2. Rotated Image 

/rotateImage {  % imageProc angle -> -
  2 dict begin
    /angle exch def
    /img exch def

    gsave
      0.5 0.5 translate
      angle rotate
      -0.5 -0.5 translate
      img exec
    grestore
  end
} def

1.12.3. Perspective Transform 

/perspectiveImage {  % imageProc skewX skewY -> -
  3 dict begin
    /skewY exch def
    /skewX exch def
    /img exch def

    gsave
      [1 skewY skewX 1 0 0] concat
      img exec
    grestore
  end
} def

1.13. Advanced Image Techniques

1.13.1. Image Mosaic 

/imageMosaic {  % imageProc tileSize -> -
  2 dict begin
    /size exch def
    /img exch def

    0 size 100 {
      /y exch def
      0 size 100 {
        /x exch def

        gsave
          x y translate
          size size scale

          % Small version of image
          0.1 0.1 scale
          img exec
        grestore
      } for
    } for
  end
} def

1.13.2. Image Outline 

/imageOutline {  % imageProc -> -
  gsave
    % Draw image as path outline
    1 setlinewidth
    0 setgray

    % Convert to path and stroke
    % (simplified - actual edge detection is complex)
    0 0 1 1 rectstroke
  grestore
} def

1.14. Performance Tips

1.14.1. Optimize Image Size 

% Bad: huge image for small display
2400 1800 8  % 2400x1800 pixels
[2400 0 0 -1800 0 1800]
{...massive data...}
image

% Good: appropriate resolution
300 225 8    % 300x225 pixels (scaled)
[300 0 0 -225 0 225]
{...reasonable data...}
image

1.14.2. Use Appropriate Bit Depth 

% Bad: 8-bit for simple pattern
8 8 8
[8 0 0 -8 0 8]
{<FF FF FF FF 00 00 00 00>}
image

% Good: 1-bit for binary pattern
8 8 1
[8 0 0 -8 0 8]
{<FF 00>}
image

1.14.3. Stream Large Images 

% Good: stream from file
/imageFile (image.dat) (r) file def

100 100 8
[100 0 0 -100 0 100]
imageFile
image

imageFile closefile

1.15. Best Practices

1.15.1. Always Specify Image Matrix 

% Good: explicit matrix
100 100 8
[100 0 0 -100 0 100]
{<...>}
image

% Bad: relying on defaults
100 100 8
matrix
{<...>}
image

1.15.2. Use Appropriate Color Space 

% Good: grayscale for B&W
100 100 8
[100 0 0 -100 0 100]
{<...>}
image

% Bad: RGB for B&W
100 100 8
[100 0 0 -100 0 100]
{<...>}
false 3
colorimage

1.15.3. Proper State Management 

% Good: isolated transformation
gsave
  100 100 translate
  200 150 scale
  % Draw image
grestore

% Bad: permanent transformation
100 100 translate
200 150 scale
% Affects everything after

1.16. Common Pitfalls

1.16.1. Wrong Matrix Orientation 

% Wrong: upside-down image
100 100 8
[100 0 0 100 0 0]  % Positive y scale
{<...>}
image

% Correct: proper orientation
100 100 8
[100 0 0 -100 0 100]  % Negative y scale, offset
{<...>}
image

1.16.2. Mismatched Data Size 

% Wrong: data doesn't match dimensions
10 10 8  % 10x10 = 100 bytes needed
[10 0 0 -10 0 10]
{<FF FF FF>}  % Only 3 bytes!
image

% Correct: proper data size
10 10 8
[10 0 0 -10 0 10]
{<...100 bytes...>}
image

1.16.3. Forgetting Color Count 

% Wrong: missing color count for colorimage
100 100 8
[100 0 0 -100 0 100]
{<...>}
false
colorimage  % ERROR: needs color count!

% Correct
100 100 8
[100 0 0 -100 0 100]
{<...>}
false 3  % 3 components (RGB)
colorimage

1.17. See Also

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