I Will Not Shot in RAW

Started May 19, 2013 | Discussions thread
Don_Campbell
Senior MemberPosts: 1,088
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Re: I Will Not Shot in RAW
In reply to peevee1, May 21, 2013

peevee1 wrote:

Don_Campbell wrote:

Raw images in the SX50 are made of 12-bits per color channel. That means these color channels have 4096 different intensities.

Probably a little less as there are usually special values on the bottom of the scale. But this has small effect. What has large effect on the number of truly different values is noise - DxOMark measures SNR at about 30 dB at the base ISO, meaning there are approximately 1000 truly different values corresponding to about 10 bits, and the other 2 bits contain noise. By ISO 400 or so useful information falls to 8 bits.

Yes, 4096 is a bit of an overstatement. A full 12-bits of golden signal is not there in the raw image but I think your statement about 10-bits understates somewhat the significance of obtaining and processing 12-bit data.

The 30db number is at the 18% gray level of signal if I read DxO's material correctly. The SNR is different at different intensities of illumination and so to get the most of your exposure of the full scene you will require an AD conversion range that goes beyond the specification of SNR at 18% gray.

In other words, we're back to the reality that if you are going to capture the full dynamic range of the signal across the full image and at all levels of illumination intensity you will likely need that 12-bit range.

The camera's built-in processing from raw to JPG is quite good under a wider range of conditions than other P&S cameras I've owned. That makes the JPG a very acceptable image for many shots and for many users. Clearly the built-in software can pick the right 8-bits of data out of the 12-bit range a lot of the time--and clearly the camera's processor is taking advantage of the wider dynamic range of the raw data. That doesn't eliminate the advantage of being able to fix things after the fact from the raw level instead of fixing things from an 8-bit per channel JPG.

As usual, for a camera with small pixels the advantage you can get out of RAW is smaller than what you can get out of certain large-pixel cameras with 14-bit RAW and DR of 14EV.

The SX50's 11.2 EV DR requires more than a 10-bit AD to capture and more than a 10-bit raw to represent. Yes, it's not a DSLR but it gives us 12-bit raws that are more useful under some circumstances than 8-bit JPGs.

Regards,

Don

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