Exporting a PNG cropped to the barcode

[mogwai]

I'm trying to generate a png of a datamatrix but its giving me this:

I'm catting the following code to the ps file.

0 0 moveto
(123458) () /datamatrix /uk.co.terryburton.bwipp findresource exec 
showpage

./gs -dBATCH -dNOPAUSE -sDEVICE=png16m -sOutputFile=test.png genBarcode.ps

How can I remove the white space?

[terryburton]

To be accurate you would typically your would use a multi-pass process.

First obtain the bounding box for the image. You'll need to use offset coordinates since GhostScript only calculates the bounding box for the first quadrant:

gs -dQUIET -dNOPAUSE -dBATCH =dSAFER -dNOEPS -sDEVICE=bbox -sPAGEOFFSET=<offset> genBarcode.ps

Calculate the width and height and determine the translation (x,y) required to snap the lower-left basepoint to 0,0.

Insert a x y translate statement into the EPS.

Re-render the image with an adjusted basepoint and fixed page size:

gs -dQUIET -dNOPAUSE -dBATCH -dSAFER -dDEVICEWIDTHPOINTS=<width> -dDEVICEHEIGHTPOINTS=<height> -sDEVICE=png16m -dTextAlphaBits=4 -dGraphicsAlphaBits=1 genBarcode2.ps

In all cases be sure to get the rounding right to avoid clipping the edge of the symbol.

[mogwai]

So for example if the width and height of the generated image was (20,20) then we'd insert a -20 -20 translate statement into 2nd pass script?

[terryburton]

You would translate to the negated values of the lower-left basepoint of the bounding box for the offset image in order to shift the image to the 0,0 coordinate.

You would set DEVICE{WIDTH,HEIGHT}POINTS to the width and height of the bounding box.

[mogwai]

Thank you for your fast reply Terry. I managed to get it working but to make it clear for other people:

1. Append to the base script the command your interested in using:

...
%!PS

0 0 moveto (asda) (includetext  rotation=45) /datamatrix /uk.co.terryburton.bwipp findresource exec 
showpage

2. Run the new file you created with the output device being set to bbox -sDEVICE=bbox giving you the bbox of the item:

./gs -dBATCH -dNOPAUSE -sDEVICE=bbox genBarcode.ps

%%BoundingBox: -1 0 25 25
%%HiResBoundingBox: -0.008930 0.000000 24.011999 24.011999

3. Modify the script from step 1 to now include the translate you require

0 0 moveto (asda) (includetext  rotation=45) /datamatrix /uk.co.terryburton.bwipp findresource exec 
translate 0.008930 0
showpage

4. Run the script again but specify the output file, width, height, etc

./gs -dBATCH -sPAGEOFFSET=4000 -dNOPAUSE -dSAFER -dNOEPS -sDEVICE=png16m -sOutputFile=out.png -dTextAlphaBits=4 -dGraphicsAlphaBits=1 -dDEVICEWIDTHPOINTS=24.011999 -dDEVICEHEIGHTPOINTS=24.01199 genBarcode.ps

You should have a png in your directory called out.png

[terryburton]

It's important to include -sPAGEOFFSET= in the initial request, otherwise the parts of the image that extend below or to the left of the origin (e.g. human readable text in EAN symbols) will be ignored in the boundingbox calculation.

[mogwai]

What would the offset be set to?

[terryburton]

Anything sufficiently large to ensure that everything is translated into the first quadrant. This need to do this arises from a GhostScript limitation.

I generally find -sPAGEOFFET=4000 to be more than enough.

[mogwai]

Amazing thank you Terry, I've updated my instructions in the previous comment