Re: compresslevel and png graphics (mkiv)

[Peter Rolf <indiego@gmx.net>]

Am 25.05.2011 21:54, schrieb Hartmut Henkel:
> On Wed, 25 May 2011, Hans Hagen wrote:
>> On 25-5-2011 2:43, Peter Rolf wrote:
>>>
>>> I just made a one pager (TEXpage) out of a big png graphic
>>> (5900x4094). The compressed size of the graphics is normally around
>>> 1.37MB on the highest png compress level (9) and 1.32MB after using
>>> optipng (only around 3% reduction this time). To my surprise the
>>> size of the final PDF was about 2.3MB. After adding
>>> '\pdfcompresslevel9' the size went down to 1.48MB. Still not what I
>>> wanted...
>>>
>>> So I was wondering: is there an option to embed the png graphic as
>>> it is (no re-compression)?
> 
> 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.
>
Sigh, most of my graphics use (and need) transparency.
So the only advantage I get from optipng is the smaller file size on my
disk. Sad, but good to know. ;-)

> Preprocessing the PNG, e. g., by convert, sometimes changes it that it
> gets copyable. Obviously flattening transparency also helps.
> 
> Anyway direct embedding or not can have positive or negative influence
> on the PDF file size. E. g. if a PNG is copied verbatim, and it contains
> lots of meta-data info, the PDF file will probably get larger, since
> normal PNG embedding removes all these info chunks.
>
And what about icc profiles?

> Another factor influencing the size is if it's PDF-1.4 or PDF-1.5: If
> you have a 16 bit PNG, for PDF-1.4 it will be automatically reduced to 8
> bit by luatex and pdftex, so suddenly the PDF file gets smaller, but
> actually also the image quality (silently) went down.
> 
> 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. :-)

Thanks Hartmut for the very detailed and interesting answer.

Regards, Peter

>> Otherwise the time consuming usage of optipng would be a complete
>> waste of time. Believe it or not, but size matters :-)
> 
> yes :-)
> 
>> This one is for Hartmut to answer. Keep in mind that pdf does support
>> pgn and jpg compression, which is not the same as 'inclusion as-is'.
> 
> fwiw, jpg is always embedded literally (no re-compression).
> 
>> The compresslevel concerns copyright free zip compression of streams
>> (that can happen to gave image data).
> 
> Regards, Hartmut
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