Bitmap to Acrobat PDF Image Conversions

Bitmap to Acrobat PDF Image Conversions

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Conversions Between .BMP Bitmaps and Postscript Arrays-of-Strings and Images
Don Lancaster Synergetics, Box 809, Thatcher, AZ 85552 copyright c2007 as GuruGram #84 (928) 428-4073

The PostScript two dimensional array-of-strings can be a very potent method to
create, hold, or extensively modify x-y data that eventually is to become your final graphic images. Such images may be calculated anew. Or they may be changes or improved transformations in existing earlier image formats. In this GuruGram, we will look at the needed conversions in getting from .BMP bitmaps to PostScript array-of-arrays and their more powerful array-of-strings relatives. Plus the methods of converting those array formats back into PostScript color images for Acrobat .PDF presentation or into traditional .BMP images.

PS Array of Strings
A PostScript array can normally be any mixed group of data types. A specialized form of a PostScript array is the string. Strings are arrays which have all of their values strictly limited to 8-bit positive integer values in the range of 0 to 255. Besides their obvious typographical uses, strings have many advantages over a generic array. Strings store much more compactly, can be read from or written to as files, and have many additional special commands available to them. While still behaving in pretty much the same manner as an array when accessed by such operators as get, put, or forall. Thus, there can be compelling advantages to storing and manipulating 8-bit x-y data in the form of an array-of-strings, rather than a generic array-of-arrays. Typically, each string will represent one row of data, while the array will hold the successive rows making up a composite image. Some older candidates for internally generated strings-as-arrays updating might include this fractal fern, this CIE Diagram, these electric field plots, this power animation demo, or these pixel interpolation maps. Two examples of .BMP bitmap to array-of-strings back to bitmap might include this image or this one. Along with similar product photo improvements that can end up highly useful for generating eBay sales.
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Here are some important uses for PostScript array-of-strings techniques...
� - Calculated PS x-y data to PS image conversions. � - Calculated PS x-y data to .BMP bitmap conversions. � - External .BMP bitmap to PS image conversions. � - .BMP bitmap to .BMP bitmap transformed improvements. � - Upgraded false color and rainbow presentations. � - Exploring new PostScript-as-Language opportunities.

A set of array-of-strings utilities has been newly posted as AOSutil1.psl . While fully compatible with our ongoing series of Gonzo Utilities, the Gonzo utilities themselves are not absolutely required for their use. As is usual, the Distiller in full versions of Acrobat makes an excellent host based PostScript-as-Language interpreter. As does Ghostscript. But there is one major new gotcha we should mention here...
Versions 8.1 and higher of Acrobat Distiller default to preventing general file reads or writes. The workaround is to run Distiller from the Windows command line using "acrodist -F" . Solutions for other operating systems are found here.

Some PS String Utilities
We can start off with this string merging proc lifted from our Gonzo Utilities...
/mergestr {2 copy length exch length add string dup dup 4 3 roll 4 index length exch putinterval 3 1 roll exch 0 exch putinterval} def

This can be useful when combining a filename with its required full pathname. Our usual reminder here that PostScript strings must use a double reverse slash any time a single reverse slash is needed. Converting from a string to a generic array is fairly trivial...
/string2array {mark exch { } forall ] } store -- 84 . 2 --

Ferinstance, a (Hello!) string2array should return [72 101 108 108 111 33]. Converting from an array consisting exclusively of 8-bit integers to a string can be done with this rather obtuse code...
/array2string {dup length string dup /NullEncode filter 3 -1 roll {1 index exch write} forall pop } def

As an example, [72 105 32 116 104 101 114 101] array2string should return a (Hi there). This utility creates a string the same length of the array. It then modifies the string so it can be written to as a file. All of the 0-255 array values are then written into the string. Sneaky, huh? Since a string is an array, these conversions should be rarely needed. And are best avoided. But they can be handy for reading a string whose data would otherwise appear as a bunch of control characters and strange symbols. Or in converting array data so it can be read or written as a file. Or, as we will soon see, in creating test arrays-of-strings.

Strings as Files
By suitable use of PostScript's filter commands, strings can become data sources or targets that can be read from or written to as files. But subject to a strict 65K maximum length limit. Thus, while strings can be used to hold entire small format x-y data, they are better used as row elements in a two dimensional array-of-strings for larger images. Here is a string reading demo...
/str1 (This is a test) store /file1 str1 0 (%EOF) /SubFileDecode filter store Example: 6 { file1 read pop == } repeat should return 84 104 105 115 32 105. %

And here is a string writing demo...
/str2 (zzzzzzzzzzzzzzzzzzz) store /file2 str2 /NullEncode filter store Example: file2 65 write file2 66 write file2 67 write should return (ABCzzzzzzzzzzzzzzzz)

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Our Array2string proc we just looked at used this scheme. Note that you can use the setfileposition command to write data in random or nonsequential locations. As with any PostScript file, you should close these when you are finished using them. As in file1 closefile or file2 closefile.

Generating Array-of-strings Test data
It can be useful and interesting to create several short strings of test data. You can use these to debug your image conversion procs while still having a manageable amount of reportable data. Three arrays-of-strings can normally be used together, one each for your red, green, and blue pixel planes...
/redAOS [ [250 250 0 0 0 250 ] array2string [100 100 100 100 100 100 ] array2string [100 100 100 100 100 250 ] array2string ] store

/greenAOS [ [ 0 250 250 250 0 0 ] array2string [100 100 100 100 100 100 ] array2string [100 100 100 100 100 0 ] array2string ] store /blueAOS [[ 0 0 0 250 250 250 ] array2string [100 100 100 100 100 100 ] array2string [100 100 100 100 100 0 ] array2string ] store

This particular arrays-of-strings data set could represent an image or bitmap that is six pixels wide by three high. Having a saturated rainbow on its bottom row, and the rest gray except for a red pixel at upper right.

Image Conversions
While the PostScript image operator is normally used with files or strings, image can also be used with any procedure that exclusively returns string values. Here are three procs that can repeatedly return arrays-of-strings for you...
/getredAOSrow { redAOS AOSrowcount get} store /getgreenAOSrow { greenAOS AOSrowcount get} store /getblueAOSrow { blueAOS AOSrowcount get /AOSrowcount AOSrowcount 1 add store } store

These assume an AOSrowcount variable that we will define below. We also assume a red-green-blue pixel sequence as is needed by a PostScript image, but not by a .BMP bitmap. As we will shortly see.
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There are several major differences between the PostScript image operator and the .BMP bitmap file format. Here are the...
PS IMAGE PROPERTIES: The image often builds rapidly from left to right and slowly from bottom to top. The image maps to a unit square that is later modified as needed by the CTM matrix. The supplied image data sequence must be red then green then blue. No header is used. End of row zero padding is neither used nor allowed.

Here is one possible PostScript Array-of-strings to image converter...
/convertAOStoPSimage { > dup begin image end } bind store

This differs slightly from the normal use of image and an image dictionary. We add a custom proc of AOSrowcount to the usual dictionary. Besides its internal use, we place a copy on the dictionary stack. Letting AOSrowcount be modified by our image conversion procs. Otherwise, the image operator behaves as described in the PostScript Reference Manual. Note particularly the usual image convention: The image is first mapped into a unit square by the DataSource matrix. In the rest of your proc, that unit square should get scaled, rotated, and translated as needed to your final size and shape by the CTM Current Transformation Matrix. At the very least, you will usually want to scale by Width and Height.
-- 84 . 5 --

The .BMP Bitmap Data Format
.BMP image files are uncompressed and lossless. They give you immediate access

to individual red, blue, and green pixels. There will be no generation loss with repeated use. When used outside of PostScript or Acrobat, Bitmaps are often your best choice when creating or modifying images. Only after the image is in its final form should more compact compressed distribution formats be used. A detailed review of bitmap format data appears here. A bitmap format file consists of an initial header and a following bitmap data area. While there are several variations on the bitmap data format, we will concern ourselves here only with the 24-bit uncompressed RGB color mode. There are several crucial differences between the bitmap data area and a PostScript image...
BITMAP IMAGE PROPERTIES: The image always builds rapidly from left to right and slowly from bottom to top. The image will be x pixels wide by y pixels high. The single file image data sequence must be blue then green then red. A header must be used. End of row zero padding normally must be provided.

Here is how the .BMP header is usually organized....
00 - 01 02 - 05 $00 - $01 $02 - $05

ASCII 2-byte "BM" bitmap identifier. Total length of bitmap file in bytes. Four byte integer, LSB first. Reserved, possibly for image id or revision. Four byte integer, LSB first. Offset to start of actual pixel data. Four byte integer, LSB first. Size of data header, usually 40 bytes. Four byte integer, LSB first. Width of bitmap in pixels. Four byte integer, LSB first.
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06 - 09

$06 - $09

10 - 13

$0A - $0D

14 - 17

$0A - $11

18 - 21

$12 - $15


22 - 25

$16 - $19

Height of bitmap in pixels. Four byte integer, LSB first. Number of color planes. Usually 01 Two byte integer, LSB first. Number of bits per pixel. Sets color mode. Two byte integer, LSB first. 1 - Monochrome 4 - 16 lookup colors 8 - 256 lookup colors 16 - 65,536 lookup colors 24 - 16,777,216 RGB colors 32 - 16,777,216 RGB colors + alpha

26 - 27

$1A - $1B

28 - 29

$1C - $1D

30 - 33

$1E - $21

Non-lossy compression mode in use Four byte integer, LSB first. 0 - None 1 - 8-bit run length encoded 1 - 4-bit run length encoded

34 - 37

$22 - $25

Size of stored pixel data Four byte integer, LSB first. Width resolution in pixels per meter Four byte integer, LSB first. Height resolution in pixels per meter Four byte integer, LSB first. Number of colors actually used. Four byte integer, LSB first. Number of important colors Four byte integer, LSB first.

38 - 41

$26 - $29

42 - 45

$2A - $2D

46 - 49

$2E - $31

50 - 53

$32 - $35

Much of a header is boilerplate that can simply be copied. But items of crucial concern are the total file length, the width of the bitmap in pixels , and the height of the bitmap in pixels. The header with these details must be absolutely correct for a bitmap to operate properly. There is another detail to bitmaps that has caused untold grief...
All new bitmap rows MUST start on a 32-bit boundary!

-- 84 . 7 --

Since three does not divide into four all that well, certain of your row widths will need 00 padding bytes added to them to guarantee this rule. Here is one possible PostScript code fragment that can calculate the padding correction for you...
/padding xpixels 4 mod [ 0 3 2 1 ] exch get store % find 32-byte start % save as correction

This code returns an integer from 0 to 3. Which tells you how many padding bytes to add. xpixels in this example is the bitmap width.

Output .BMP Bitmap File Conversions
Getting from PostScript arrays-of-strings to a .BMP bitmap for any use outside of Acrobat or PostScript can be somewhat more complex than an internal image conversion. There are two steps to the process that involve writing a header and then transferring the data in the proper order along with the padding bytes...
/convertAOS2BMPimage { /bmpoutfile arrayfilepathprefix outputbitmapfilename mergestr (w) file store % make bmp write file

/xpixels redAOS 0 get length store % calc bmp data /ypixels redAOS length store /padcount xpixels 4 mod [0 3 2 1] exch get store /totalbmpsize xpixels padcount add ypixels mul 54 add store bmpoutfile 66 write bmpoutfile 77 write % calc bmp padding

% calc file length


totalbmpsize 256 3 exp cvi idiv % calc length bytes /byte4 exch store totalbmpsize 256 3 exp cvi mod /res3 exch store res3 65536 idiv /byte3 exch store res3 65536 mod /res2 exch store res2 256 idiv /byte2 exch store res2 256 mod /byte1 exch store bmpoutfile byte1 write bmpoutfile byte2 write % write length % as modulo 256 -- 84 . 8 --

bmpoutfile byte3 write bmpoutfile byte4 write 4 {bmpoutfile 0 write} repeat bmpoutfile bmpoutfile bmpoutfile bmpoutfile bmpoutfile bmpoutfile bmpoutfile bmpoutfile bmpoutfile bmpoutfile bmpoutfile bmpoutfile bmpoutfile bmpoutfile bmpoutfile bmpoutfile bmpoutfile bmpoutfile bmpoutfile bmpoutfile 4 4 4 4 4 4 54 write 0 write 0 write 0 write 40 write 0 write 0 write 0 write % four reserved nulls % start of data offset

% write data header size

xpixels 256 mod write xpixels 256 idiv write 0 write 0 write ypixels 256 mod write ypixels 256 idiv write 0 write 0 write 1 write 0 write 24 write 0 write 0 0 0 0 0 0 write} write} write} write} write} write} repeat repeat repeat repeat repeat repeat

% write x size lsbs % assume < 65K

% write y size lsbs % assume < 65K

% number of bit planes % write color mode

{bmpoutfile {bmpoutfile {bmpoutfile {bmpoutfile {bmpoutfile {bmpoutfile

% % % % % %

compression mode pixel data size width resolution height resolution colors used important colors

This completes writing the header portion of our .BMP bitmap file. We continue by writing the pixel data bytes in BGR order and the end-of-row padding bytes...
0 1 ypixels 1 sub {/currow exch store % start data write

/curred redAOS currow get store % grab RGB row data /curgreen greenAOS currow get store /curblue blueAOS currow get store -- 84 . 9 --

0 1 xpixels 1 sub {/curpos exch store % BGR pixel write bmpoutfile curblue curpos get write bmpoutfile curgreen curpos get write bmpoutfile curred curpos get write } for % finish row padcount {bmpoutfile 0 write } repeat } for bmpoutfile closefile } bind store % add row padding

% finish image % close file % and exit

This proc needs your arrayfilepathprefix path and outputbitmapfilename filename predefined. As well as having the correct pixel data in redAOS, in greenAOS, and in the blueAOSarrays of strings.

Input .BMP Bitmap File Conversions
A somewhat similar process can be used to capture data from an input .BMP file and move it into redAOS, greenAOS, and blueAOS arrays-of-strings for further transformation or PostScript image conversion...
/inputbitmap2AOS { /bmpinfile arrayfilepathprefix inputtbitmapfilename mergestr (r) file store bmpinfile read pop 66 eq bmpinfile read pop 77 eq and bmpinfile 26 setfileposition bmpinfile read pop 1 eq and not {NOT_A_BITMAP_FILE!} if bmpinfile 28 setfileposition bmpinfile read pop 24 eq not {NOT_24_BIT_COLOR!} if bmpinfile 10 setfileposition bmpinfile read pop % START ANALYSIS % create .BMP read file

% check for ok format % "B" as first character? % "M" as second char? % one color plane?

% report bitmap error % report color message

% find the offset

-- 84 . 10 --

bmpinfile read pop 256 mul add /offset exch store bmpinfile 18 setfileposition bmpinfile read pop bmpinfile read pop 256 mul add /xpixels exch store bmpinfile 22 setfileposition bmpinfile read pop bmpinfile read pop 256 mul add /ypixels exch store /padcount xpixels 4 mod [0 3 2 1] exch get store /redAOS ypixels array store /greenAOS ypixels array store /blueAOS ypixels array store % find the xpixels

% find the ypixels

% calculate padding

% empty AOS arrays

0 1 ypixels 1 sub {/rowcount exch store bmpinfile offset rowcount xpixels 3 mul padcount add mul add setfileposition % % % %


go to row start X3 for triads plus padding set row start % create rows

/redAOSrow xpixels string store /greenAOSrow xpixels string store /blueAOSrow xpixels string store

0 1 xpixels 1 sub {/posn exch store % for each pixel triad blueAOSrow posn bmpinfile read pop put % blue greenAOSrow posn bmpinfile read pop put % green redAOSrow posn bmpinfile read pop put % red } for % till row done

redAOS rowcount redAOSrow put % place strings greenAOS rowcount greenAOSrow put blueAOS rowcount blueAOSrow put } for } bind store % for each row % completing proc

Four header bits are checked to verify you have a valid 24 bit .BMP color file. Offset, x position, and y position data is then extracted and modulo 256
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converted. Padding bytes are then calculated, allowing you to find the actual start location of each data row. New arrays-of-strings are defined for the blue, green, and red planes. Three row long work strings are created. These get filled in a blue-green-red sequence. The row strings are then placed in their appropriate array-of-strings positions. The proc requires a predefined arrayfilepathprefix path and an inputtbitmapfilename filename.

PS Image to .BMP Bitmap File Conversions
Getting from a PostScript or Acrobat image to a .BMP bitmap is highly application dependent. There are a number of commercial and shareware utilities that ease this task, so we will not go into much detail here. If the original sourcecode is available, you may want to gather in the original data file or file triads, optionally converting these sources to an array-of-strings. From there, our convertAOS2BMPimage could be directly used. If only the .PDF output file is available, you can print to disk uncompressed Level I to try and recapture the original image data stream. See PDFEDIT1.PDF for some tutorial guidelines. A reminder that a .BMP file needs a header, reads its color triads "backwards" as blue-green-red, and may need end-of-line row padding per our above code example. Note that you will often get the best results by matching the source file x and y pixels to the .BMP bitmap size. Any scaling may introduce artifacts and generation loss.

For More Help
The speeds of these routines are more than acceptable, taking a fraction of a second per megapixel on faster machines with newer versions of Acrobat Distiller. The intent is to use these routines to improve some of our older calculated x-y data sets so they can be presented in a faster, more standard, and more compact Acrobat image formats. Thus significantly both shortening and speeding up the ultimate distribution .PDF files. I would also like to use these utilities as the core components for .BMP to .BMP transformations that go far beyond what is offered in standard image processing programs. Giving you total control and the open ability to explore six ways from Sunday. Improved perspective correction and image rectification are two of my important current needs. Similar tutorials and additional support materials are found on our PostScript and our GurGram library pages. As always, Custom Consulting is available on a cash and carry or contract basis. As are seminars. For details, you can email Or call (928) 428-4073.
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