November 10, 2004
Canon EOS 10D/20D JPEG conversion errors?

NoelC has posted a thorough piece on the apparently flawed RAW -> JPEG algorithm in the Canon EOS digital cameras:

I looked at the exposure histograms for each of the color channels in an image I shot - which by the way had a luminance histogram on the camera that didn't touch the right side. Sure enough, in the images with the fuzzy/texture-lacking bright red objects, the red histogram had data climbing the right side of the image. Yet not in all cases. Some images with fuzzy reds had red channel data close to the right side, but not touching.

In looking at the channels in the images that weren't overexposed, one thing became clear: As the reds get pretty bright (upper-quarter of the histogram), they start to lose definition. This says the Canon demosaic/color generation algorithms may just have a small quirk - a characteristic that bright red objects lose definition.

All right, I thought, what if a different conversion algorithm were employed. Would the results be the same? I tried shooting a raw photo of red flowers and converting it in Adobe Camera Raw. What would happen? Amazingly, with some negative exposure compensation the reds came out vibrant, sharp, and full of texture.

Consider these images, the first is from the embedded JPEG Canon put in the Raw file, and the second is from the conversion through Adobe Camera Raw (Photoshop CS):

Check out the original post with photos and other users' experiences at

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Interesting. It seems that it might not be restricted to Canon EOS digital cameras either! I've never saved the images from my Canon S70 in RAW format before either, even though it does have that capability - but then I don't look that closely at my photos to notice fuzzy reds. I'll take a close look next time I take a photo of something red :)

Posted by: alkam on November 11, 2004 12:13 AM
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