RAW Vs. SRAW..

Started Dec 27, 2007 | Discussions thread
John Sheehy Forum Pro • Posts: 20,236
Re: To the understanding of sRaw

rrcphoto wrote:

John Sheehy wrote:

If Canon wants to make smaller files, they can start by dropping
worthless, marketing-gimmick bits from the RAWs. ISO 100 only needs
12 bits; ISO 3200 only 9 bits without losing any shadow detail. The
dropped bits are less compressible than the ones that remain.

well, in the case of the 40D, there's provable increase in DR of
around 1/2 stop in the shadows (as per dpreview), and they are
assuming it's because of 14 bit mode.

No, it's because there is less analog noise. Read noise at IS0 100 is about 1.4 12-bit ADUs in the 40D, while it is about 2.1 ADU in 30Ds. That's 1/2 stop. If you quantize the 14-bit 40D RAW to twelve bits, it is still limited by the analog noise, and quantization has no impact on IQ.

You CAN'T judge the value of 14 bits against 12 bits by comparing them on different cameras. Even cameras like the D300 that offer both have other differences besides bit depth involved (readout/burst speed).

also the overall lattitude of
a 40D RAW file is more than a 30D raw file ... and that's with an
increased pixel density.

Well, DR and exposure latitude go hand in hand. The only difference is that you may accept more shadow noise for a DR standard than a latitude standard.

so I'm not quite sure it's "worthless".

I know it's worthless, unless you're an astrophotographer stacking 16 images, in which case the tiny bit of signal in the extra bits may wind up becoming visible.

it's a YMMV thing on whether
or not what it captures is important to your photography and what you
do with the RAW data.

I think even the astrophotography only benefits ever so slightly from the extra bits; the person shooting a single frame on their camera gets nothing out of the extra two bits that they're ever going to see, because the difference is trivial compared to the dynamics of analog read noise.

I have a feeling we're going to be seeing alot of sRAW .. as canon
has been whispered around that it's next rendition of sensor
technology will really focus on the hardware binning as methods of
reducing noise (purportedly a 2 stop gain in ISO noise) - and I
would presume they could also increase DR with clever binning as
well), as the 40-60Mp low voltage CMOS sensors are the next
significant generation of canon sensors.

Hardware binning is only going to reduce image read noise (software binning never does - it only reduces pixel noise); shot noise is a big part of the high-ISO issue, too, and binning doesn't have any benefit whatsoever for image shot noise. Binning is a big hype that will never deliver what it is supposed to, IMO, except as a marketing gimmick for people naive enough to think that looking at a reduced-resolution image with less pixels but the same image noise, is a good thing. If you have photoshop, you can simulate at least software and shot noise binning (IOW, everything but hardware read noise binning) with the Pixelate~Mosaic filter. Unless the noise is patterned at the same frequency as your pixelation would be, pixelating (binning) only makes the noise grains bigger as it makes it shallower, and trashes subject detail at the same time. You can see less of what you tried to capture. It's a totally false economy, and I can't believe that so many people believe in it.

I have my doubts about hardware binning, too, at least in the immediate future. The biggest obstacle with sensor technology and read noise, as it affects DR, is the inability to get read noise below a certain level, relative to the full DR of the readout. All of the highest-DR cameras right now are stuck at the same max_signal-to-readnoise level; 1.25 ADU for 12-bit systems, 5 ADU for 14-bit systems, and 20 ADU for 16-bit systems.

The cameras that keep RAW read noise at bay at higher ISOs can do so ONLY BECAUSE THEY ARE READING A LOWER NUMBER OF MAXIMUM ELECTRONS. They can not maintain the same low read noise as measured in electrons when counting more of them, and that is exactly what binning will entail. Read noise of the binned pixel will be similar to read noise of the single pixel at 1/4 the ISO.

I don't believe a word Canon or any other manufacturer says about their upcoming products. It's almost always basesless hype.

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GDi
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