Legacy ImageMagick Discussions Archive

After some "more" fiddling with IM 6.6.9-4 Q64 + HDRI
I have stumbled a strange JPG bug ...

Whenever the image is Identified as "8-bit PseudoClass 256c" both "convert" and IMDisplay simply show a "black" image ...

identify dsc1860b.jpg
dsc1860b.jpg JPEG 1288x989 1288x989+0+0 8-bit PseudoClass 256c 176KB 0.047u 0:00.092



In IMDisplay it is completly black ...



Nonetheless if I call "convert -monitor dsc1860b.jpg -distort resize 20% -auto-level tt1.jpg"

Load image[dsc1860b.jpg]: 988 of 989, 100% complete
Level image[dsc1860b.jpg]: 197 of 198, 100% completee
Save image[tt1.jpg]: 197 of 198, 100% complete

I get a "damaged" image like this ...




Using manually compiled Windows version with HDRI quantum 64 - 6.6.9-4
Any ideas ?

After some tests I noticed that the previous problem is not appearing if I compile with Q16 or Q32 ...

Still keeping the HDRI flag ON ... ( or at least is what the "convert -version " reports ...

So now the this kind of JPG image ( tested with IMDisplay) is now correct ....

Even calling the "-auto-level" option works correctly and does not give the previous problem ...



Somewhere in the JPG library there is a "problem" with Quantum 64 ...

Strange why are affected the "Pseudo Class 8 bit 256c" JPGs ?

Comments ?

We don't advertise Q64 because it has not yet been validated and will produce incorrect results in some cases. Whenever ImageMagick is compiled with HDRI support, use Q16 as the quantum depth.