Tk Source Code

If maxval in PPM file header is greater than 255 then the
following will happen:

$ wish
% image create photo f -file x.ppm
PPM image file "x.ppm" has bad maximum intensity value 65535

and no image will be created.

Create x.ppm:
$ xwd -root | xwdtopnm >x.ppm
The maxval depends on the X servers display depth value.

Fix was indeed nice and localised. In 8.5 and 8.6 trees.

The format definition for P6 states that maxval can be up to 65535, with maxvals > 255 indicating that 2 bytes per channel per pixel are to be used (instead of 1).

We should fix (though we will lose information; Tk uses strictly 32 bits per pixel, with 8 for each of R, G, B, and alpha). Priority not very high as this is a fairly rare format variation (and we'll never write it from photo images), but the changes should at least be quite localised to just the PPM format handler.

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What is the magic number for the file? (First line, should be a "P" followed by a number.) I ask because Tk currently only supports a small number of the PNM formats and only a small number of widths too. This can be changed, but I need to understand more to know how to change it. :-)

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I (the submitter) forgot to provide my e-mail address: pme at prolan dot hu