Re: compresslevel and png graphics (mkiv)

[Peter Rolf <indiego@gmx.net>]

Am 26.05.2011 18:17, schrieb Peter Rolf:
> Am 26.05.2011 12:52, schrieb Peter Rolf:
>> Am 25.05.2011 21:54, schrieb Hartmut Henkel:
> [..]
>>>
>>> no. There is a "PNG Copy" function for literal embedding of the PNG
>>> file, but that triggers only, if the file simultaneously satisfies quite
>>> a few conditions, which are about: non-interlaced, no palette, no
>>> transparency, no gamma coming with it, no gamma modification requested,
>>> no white adjustment in the PNG, and a few more rare others. Else it's
>>> de-compressed and then re-compressed to the \pdfcompresslevel, and
>>> additional streams and dicts are added. You see in the log if it finally
>>> was "PNG Copy" or not.
>>>
> [..]
>>>
>>> These are about the factors affecting the PNG to PDF size. For your big
>>> PNG graphic you may find a preprocessing (e. g., pngtopnm | pnmtopng
>>> will definitely remove all fat) that makes it compliant with the "PNG
>>> copy".
>>>
>> I will give that a try. But I doubt that there is much 'fat' on that
>> graphic. Anyhow, you never know before you have tried it. :-)
>>
> 
> No luck. I used imagemagick to convert to pnm and back.
> Transparency was removed before by adding a white background, also all
> not critical chunks (ICC profile, backgroundcolor, resolution, creation
> and modify date, comment) were removed. The graphic is a valid PNG
> (TweakPNG) and aside from the size, there is nothing special with this
> graphic. Still no '(PNG copy)'.
> 
> @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 for any inconvenience. I should have tested this case before...

Best wishes, Peter


> Regards, Peter
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