Thursday, August 28, 2008

Canon sRAW Noise and High ISO Test ( 40D reference for the 50D )

When Canon announced the 50D, the specs that caught my attention were the sRAW modes. I liked the idea of sRAW mode on the 40D but couldn't manufacture a reason to shoot a 10mp sensor at 2.5mp. It looks like the 50D will shoot it's 15mp sensor at 7mp. For some of the things I shoot that sounds worthwhile. Then I wondered if those sRAW files would be less noisy at high ISO and just had to test it...

At first I shot a variety of exposures of the same scene and cropped the full size files to match the sRAW size. A noise difference didn't jump out at me at all. What did was how much sharper the sRAW files were. It looks like I either had image stabilization on in one shot and off in the other (which I didn't), or I used a much smaller aperture to get more depth of field (which I didn't). I'll have to try this again with a tripod and manual focusing.

Then I shot black frames (lens cap on at normally fast shutter speed) at ISO 1600 and 3200 in RAW and sRAW. That's where I see a huge difference in noise. Here's the ISO 3200 comparison. I see blatant noise reduction in sRAW. The noise in sRAw seems to be all luminance and no chroma too (someone please explain that to me). I also see more noise in the 40D at 3200 than the 30D at 3200 which is not what I expected (or was advertised). And I should mention that I had to beat the heck out of these black frames to get them to look this bad/obvious.

I did this test in 5 minutes. Please leave comments if you have suggestions for improving the method.
AWB, Manual Mode, ISO 3200 and 1600, 24-70 f/2.8 @ 70mm & f/4.5 on the 40D, 70-200 f/2.8 IS @ 70mm & f/4.5 on the 30D, handheld, autofocus on middle point at closest flower, raw files 'barely processed' in Lightroom, no manipulation (everything zeroed) on the flower shots, for the black frames only exposure slider set to +4, output was full jpg at max quality.
jpgs from sRAW files cropped to 800x800 near middle of frame. 300x300 corner for black frames.
jpgs from RAW files bicubic downsized to match sRAW dimensions (1944x1296) then cropped to 800x800 near middle of frame.
for exaggerating black frame noise: cropped 300x300 bottom right corner (because noise appeared strongest there in the 40D) then up rezed 200%, brightness +50 and contrast +25 to exaggerate for visibility.

I have high hopes for the 50D and its sRAW modes now.

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