Re: compresslevel and png graphics (mkiv)

[Peter Rolf <indiego@gmx.net>]

Am 27.05.2011 15:09, schrieb Hartmut Henkel:
>>> @luigi: an ICC profile definitely breaks the <png copy> rules
>>>
>>> The only chunks left are
>>>
>>> IHDR    PNG image header: 5900x4094, 8bits/sample, truecolor,
>> noninterlaced
>>> IDAT    PNG image data
>>> ..
>>> IDAT    PNG image data
>>> IEND    end-of-image marker
>>>
>>> Mh, where is the show stopper? The compression method?
>>>
>> Looks like some of ConTeXt PDF/X-related settings is causing this. If I
>> reduce the code to the pure picture, the '(PNG copy)' is triggered.
>> Probably the active color management (default color space) is breaking
>> the copy process here.
> 
Sorry Hartmut, my last statement is complete BS. I made a 'blind' run in
my lunch break, not inspecting the pdf. And sadly I had forgotten, that
I changed the test file yesterday to use a small png test graphic
instead of my big png. *brain vs. full stomach: 0:1*

So the PDF/X settings have no influence on this. The big png is not
'copied'.
Anyhow, this is not a serious problem and honestly I don't have that
much time now. When I have some more time I will use gdb to find the
failing condition in writepng.w. Will be interesting, the last time I
used gdb is more than 10 years ago.

Thanks for all answers so far.

Regards, Peter

> must be some \pdfimageapplygamma > 0, only this and the \pdfimagehicolor
> primitive can influence this low level stuff.
> 
> Btw, just \pdfimageapplygamma > 0 (without setting \pdfgamma and \pdfimagegamma) already changes the PNG image, since the luatex (and pdftex) internal defaults are not gamma-neutral. No idea if (and then
> to which value) this should be fixed.
> 
> Regards, Hartmut

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