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Questions about CHDK Internal DNG Conversion

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Offline Sess

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Questions about CHDK Internal DNG Conversion
« on: 04 / April / 2009, 02:45:51 »
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I'm using an A650. Originally, I didn't like taking the raw files from the camera and converting them with dng4ps and stuff like that, because getting the right colors out of it depended on how well dng4ps understood the color qualities of your specific camera. In my personal experience, a few photos taken in the backyard with the pool in the shot was enough to convince me to stick with JPG.

So, now CHDK can make DNG files on its own and so I have some questions:

1. Is the quality of the internal DNG conversion still subject to CHDK's understanding of my camera? Or since it is done on the camera itself, is it somehow a more accurate, possibly perfect conversion?

2. On the Adobe Camera RAW import screen (when opening a DNG in Photoshop), for the white balance settings, does "As Shot" actually have meaning now? In other words, can I open a DNG in Photoshop and have the same white balance applied to the image that the camera would have used on a JPG?

3. I've done a few quick preliminary tests already. At a glance, the DNGs do look more pleasing than the JPGs, but they also appear more saturated. I remember something like this when I tried the dng4ps a year or so ago. So is this just more of the same?

4. To use the DNG conversion, I had to generate the badpixels.bin file using the script. Other than "run the script" there are very little instructions or explanations on this process. Does it matter what my camera is pointing at during this? Is it supposed to be a dark frame? Should I have it in a dark room?

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Offline fudgey

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Re: Questions about CHDK Internal DNG Conversion
« Reply #1 on: 04 / April / 2009, 03:15:10 »
1. Is the quality of the internal DNG conversion still subject to CHDK's understanding of my camera? Or since it is done on the camera itself, is it somehow a more accurate, possibly perfect conversion?

CHDK mostly uses the same color matrices DNG4PS-2 uses, so its output is probably identical or worse (if there are rounding errors?). There is no fancy signal processing in RAW or DNG output, kind of the idea of it all...the problem is how to tell your photo develop software how to interpret RAW CCD data, and we don't have that data so it's been experimentally found by shooting at things and analyzing the images.

But with DNG you get some real WB info from the camera embedded in a DNG (this is not available for conventional RAW), which could very likely be what's been bugging you (note that I didn't check that any of this is true for the a650, I just assumed it would be).

2. On the Adobe Camera RAW import screen (when opening a DNG in Photoshop), for the white balance settings, does "As Shot" actually have meaning now? In other words, can I open a DNG in Photoshop and have the same white balance applied to the image that the camera would have used on a JPG?

3. I've done a few quick preliminary tests already. At a glance, the DNGs do look more pleasing than the JPGs, but they also appear more saturated. I remember something like this when I tried the dng4ps a year or so ago. So is this just more of the same?

Yes, at least quite close. But if the color matrix is no good for your camera, WB can't come to rescue. Also, Canon's JPEG processing likely involves some other stuff too that could affect colors, so those "As Shot" WB coefficients CHDK now puts to DNG files may not produce identical colors. They should give you a very good starting point close to Canon JPEG, though.

4. To use the DNG conversion, I had to generate the badpixels.bin file using the script. Other than "run the script" there are very little instructions or explanations on this process. Does it matter what my camera is pointing at during this? Is it supposed to be a dark frame? Should I have it in a dark room?

I don't remember...I think it doesn't matter. The script seems to set Tv too, that's something that would change the result if your camera has more than one bad pixel list and if you are running with autoexposure.

 

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