Help me debug this imagesource? or display configuration issue?

[poisondeathray]

I get a different preview when loading this PNG image in avspmod, or vdub, or mpchc - when using ImageSource() vs. CoronaSequence(), or FFVideoSource(). The latter two have higher contrast (I think this is what it should be and appears like this in other programs like Adobe photoshop, Adobe AE, xnview, ffplay)

This appears to be a "normal" 8bit RGB PNG. There is no metadata or embedded color profile that Adobe or XNview reports.

Set's Avisynth 2.6MT x86 , but also occurs in "vanilla" Avisynth 2.6 x86

Info() with CoronaSequence reads RGB32, but it's just a dummy alpha. Info with ImageSource() reads RGB24(). It doesn't matter if I ConvertToRGB24 or 32 as expected.

I have included 3 images in the zip file , "hcw_mmtest_close.0000.png" is the source , and what I get taking a screenshot from avspmod with imagesource() and coronasequence()

3.52MB
http://www.mediafire.com/?btucr97gil959t1
or
http://www70.zippyshare.com/v/swLmlDBS/file.html


Is this an ImageSource() issue, or some other local configuration issue ?


Thanks

[poisondeathray]

Actually exiftool reports a gamma of 1 in the source image - this might be the difference . In firefox for windows, the image appears like imagesource (less contrast) too , but in image editors like photoshop, irfanview, etc.. it appears like coronasequence

Does anyone know of a "jpegsnoop" -like program for PNG ?

EDIT: TweakPNG - it also reports a gamma of 1.0



Summary - it appears different applications handle the gAMA chunk in PNG differently . If you strip it with TweakPNG, then it will give the higher contrast version in all (most) applications .

So it appears there is a difference between imagesource() and coronasequence() handling of PNG images, when there is a gamma specified


references:
http://www.libpng.org/pub/png/book/chapter10.html#png.ch10.div.2
https://hsivonen.fi/png-gamma/
http://jonathannicol.com/blog/2006/12/01/fixing-png-gamma/