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Thread: unsupported PNG verient for Precomp

  1. #1
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    unsupported PNG verient for Precomp

    first regard the PSD format.. precomp v0.37 doesnot work with it.. but here is a PSD parser.. http://www.telegraphics.com.au/sw/#psdparse .. the author wrote in his readme "* Normally, RGB images (and grey scale+alpha images) are written as composite
    PNG with channels combined in one file"
    so i used this program and it extracted the embedded png (which precomp does not recognize) i tested with stuffit v12 the result was...wooooow.. (2,232,900 bytes) while rar is (3,453,894 bytes) and 7z (3,441,798 bytes)
    then i used advdef -z0 (to remove compression).. then rar 3,315,840 bytes and 7zip 3,072,274 bytes so still far away from stuffit v12 engine.. but ifi want to make an EXE from the stuffit file.. the result 3,565,817 bytes with exe stub of 140,907 bytes so the EXE stub does not support the complete sitx format features so the main program convert it into plain sitx with now (recomp) features..

    here is the images http://rapidshare.com/files/116312661/Coat2.rar.html

    its 24bit+8bit alpha.. so i hope the complete png format is identified in precomp v0.38
    Last edited by maadjordan; 20th May 2008 at 20:00.

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    Matt Mahoney's Avatar
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    Better check the result from Stuffit. It uses lossy compression for some file formats like zip, pdf, and png.

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    original size 3,407,525 bytes

    extracted from sitx 3,594,357 bytes (larger) ..it restores the non optimized size

    if compressed again it would give same file size..(2,232,900 bytes)

    still i think its good..

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    What Stuffit does is convert png to a raw image and compress it. The decompressor converts back to png. The new image displays identical, but is not bitwise identical as you can see. It does this with a few other formats too. Stuffit calls it "pixelwise lossless".

    See http://cs.fit.edu/~mmahoney/compression/text.html#1930
    Last edited by Matt Mahoney; 20th May 2008 at 21:46.

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    i know that but if you rely on the resulted png files as original then it 100% lossless but still the main issue that precomp does not read it.. so no shanche to try lprepaq fr real comparison..i hope schnaader add it..

    regarding PSD files for photoshop refer to this PDF http://libpsd.graphest.com/files/Pho...%20Formats.pdf which indicates that since PS version CS a zib algorithem can be applied to image data so Precomp should recognizeit too..(didnot work in slow mode.. and ididnot bother -brute..)

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    First of all, the program called psdparse (to be more exact: the other tool in that package, psd2png) you mentioned doesn't extract embedded PNGs, but converts the image data found in a PSD file to PNG files. Most image data in PSD files I found is saved as raw image data. The best thing I could do about that is to add a BMP header like for PDF images so that paq8o8pre could compress them a bit better.
    Nevertheless, PNG support for Precomp has to be improved, but this is nothing new...

    I couldn't find any PSD files that use the ZIP method explained in http://libpsd.graphest.com/files/Pho...%20Formats.pdf yet, it would be nice if someone who has could upload some example files. I'll also have a look at the RLE method.
    http://schnaader.info
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