Optimizing CHDK for RAW?

KenO

122

« on: 26 / March / 2010, 17:32:12 »

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Some friends with DSLRs have recently given me some tutorials on how to optimize DSLRs for RAW shooting and so minimize noise without blowing out the R G B channels of the sensor.

While there are a number of names for this, I have had the best results searching using UniWB and ETTR. If there are any other names for this I would be interested.

One of the more complete websites discussing this is http://www.8thcross.com/2009/09/28/uniwb-a-good-tool-for-good-hdrs/ (lists 9 other websites)

What I did not realize is that most DSLRs are optimized for shooting JPGs not RAW.
http://www.pentaxforums.com/forums/pentax-dslr-discussion/68043-finally-camera-raw-histogram.html
http://www.luminous-landscape.com/tutorials/right-hista.shtml

To optimize for RAW most suggest minimizing the settings for contrast, image sharpening and saturation and either use a dark frame or completely saturated frame for determing White Balance. http://photography-on-the.net/forum/showthread.php?t=485349

Since the sensor for our Canon CHDK point & shoot cameras is smaller than these DSLRs, am wondering if CHDK can do these same things?

Since I now only shoot RAW with my CHDK Canon optimizing for JPGs is not an interest.

It was hard for me to believe that someone else did not have this idea so started searching the forum. Got no hits for UniWB and only one for ETTR http://chdk.setepontos.com/index.php/topic,638.0.html but it was started 25 / February / 2008 and ended 20 / July / 2008. This author was Last Active: 05 / December / 2008, 11:02:45. Also the discussion was not about minimizing the cameras contrast, image sharpening, saturation and White Balance settings.

Am interested to learn if these settings can be changed for any ver of CHDK?

Also hope some others may be interested in doing this.

For one of my searches I used "raw histogram" and got ~ 18,600 hits. For some reason the Pentax Forum link by dlacouture listed as "Finally, an in-camera Raw Histogram!" does not work correctly.

Ken

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KenO

122

Re: Optimizing CHDK for RAW?

« Reply #1 on: 26 / March / 2010, 17:36:26 »

Good News!

I just tried all the links and they worked. The problem was just in the Preview.

Ken

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reyalp

14082

Re: Optimizing CHDK for RAW?

« Reply #2 on: 26 / March / 2010, 18:18:42 »

Quote

To optimize for RAW most suggest minimizing the settings for contrast, image sharpening and saturation

Just to be clear: These settings do not affect the raw. The suggestion is that using them will allow you to get a better idea of the scene characteristics from a histogram built from the jpeg (or live view or whatever). The same logic should be valid for CHDK cameras, but most of them don't give you much control of the raw->jpeg process. Many don't have a contrast setting at all, or at best a special "high contrast" or "smart contrast" mode.

It would be possible to generate a true raw histogram from raws that had already been shot. This would be quite slow (probably a couple seconds if you sampled every pixel from disk, and a bit less if you took it from the raw buffer right after the shot.) A variant of this is already available in script with shot_histogram. Similar data is not available from the preview, and this is probably a hardware limitation. It might be possible to come up with some experimentally derived modification to the live histogram to give you better feedback about the raw.

expose right should be valid for CHDK raw, and there has been discussion of better supporting this in CHDK.

CHDK is a volunteer project. Features and improvements are added when a developer decides they want them, or someone posts and acceptable patch that implements them.

Forum search is broken btw.

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