Friday, August 29, 2008

Part 2: Canon sRAW Noise and High ISO Test ( 40D reference for the 50D )

The previous test was quick and had a lot of variables I didn't bother to think about. This time I did, so I eliminated what I could.

I'm trying to figure out if the sRAW mode on Canon's recently announced 50D will be useful to me. So I'm testing the sRAW mode on the 40D and here are my next round comparison shots...


I decided to eliminate the resizing variable by changing my focal length so the same number of pixels are covering the same parts of the scene (I just cropped the RAW file to the sRAW dimensions and get the same view). The first pair is underexposed and shows the noise differences well, the middle pair is a normal exposure and shows sharpness differences well, and the 3rd pair doesn't change the focal length so the RAW file had to be re-sized to match the same view.

The previous test proved to me that noise was lower using sRAW. This one agrees. The previous test also made me wonder if sRAW was sharper too. This one seems to agree, but makes me realize that the question is more complicated than that. Yes, 4 sRAW pixels are sharper than 1 RAW pixel. The middle pair shows this very well. But that's not how I'd use the camera. I'd use it like the 3rd pair, and after resizing, they are similar.

This does lead me to a valuable conclusion: I expect that canon's 50D in sRAW mode at 7mp will be sharper, and have significantly less noise than an 8mp 30D. I already expected that, but now I'm convinced the difference will be drastic and worthwhile to me.

That means it's time to upgrade! YESSSS!

Other interesting conclusions: The sRAW file size is typically half the full RAW file size, which is unfortunate because the resolution is 1/4. Also, burst mode did last a little longer. I got about 17 RAW files out at 6.5fps, but could get over 20 sRAW files at 6.5fps and the buffer cleared faster. So sRAW mode isn't so much for when you want smaller files, but for fast action bursts at high ISOs.

Details: 24-70 2.8L at 35mm and 70mm and f/8, 70-200 2.8 L IS at 200mm and f/8, 40D, manual focus with live view, on tripod, using mirror lock up and cable release. RAW and sRAW files processed in Lightroom with everything zeroed. Jpegs at highest quality while cropping and bi-cubic resizing. 40D's high ISO noise reduction was OFF this time.

1 comment:

lclevy said...

Hello,

there is important difference between sraw (1/4 size like sraw2) and sraw1 (1/2 size).

All sraw are encoded using YCbCr (luminance/chrominances blue and red). sraw (and sraw2) have 2Y 1Cb and 1Cr values each 2 pixels. sraw1 have 4Y, 1Cb and 1Cr values each 4 pixels.

more details here:
http://lclevy.free.fr/cr2/#sraw

Laurent