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chdk raw format selection

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Offline chforum

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chdk raw format selection
« on: 22 / April / 2013, 01:41:58 »
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I have a sx powershot camera; raw dng formats gives fairly clean images. Whereas cr2 and crw formats
has a green cast similar to uniwb. (both formats also have .1mb less than dng)

If both dng and crw have the same original raw data, which format would you prefer? (or suggest to use?)



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Offline reyalp

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Re: chdk raw format selection
« Reply #1 on: 22 / April / 2013, 02:12:48 »
Quote from: chforum on 22 / April / 2013, 01:41:58
If both dng and crw have the same original raw data, which format would you prefer? (or suggest to use?)
The data is the same, so use whichever one is convenient for you.

CHDK raw (generally saved with a CRW or CR2 extension) is just a framebuffer dump, it's not in the actual Canon CRW or CR2 format, and it doesn't contain any exif or other metadata. DNG is the same data, in a standard package, plus exif. So in general, DNG will probably be easier to work with. The main disadvantage is that capturing DNG is somewhat slower.

If your camera supports raw as a Canon firmware option (without CHDK), then that will be in the actual CRW or CR2 format. This is probably a good choice on the cameras that support it.
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Offline chforum

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Re: chdk raw format selection
« Reply #2 on: 24 / April / 2013, 21:10:28 »
Thanks dude.

What causes  the green cast on crw; cr2 files? How would you go about in best correcting? Set to auto wb? Or match according to jpg values?

Is there a reason raw files have the same size? Or dng is .1 mb larger than cr2; crw?
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Offline waterwingz

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Re: chdk raw format selection
« Reply #3 on: 24 / April / 2013, 21:13:10 »
Quote from: chforum on 24 / April / 2013, 21:10:28
Is there a reason raw files have the same size? Or dng is .1 mb larger than cr2; crw?
RAW files are just a dump of every pixel of your camera's sensor.   Unless the sensor size changes,  the RAW size will not change.   :haha

The DNG files are slightly larger because the contain additional header information (EXIF).
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Offline reyalp

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Re: chdk raw format selection
« Reply #4 on: 24 / April / 2013, 22:27:56 »
Quote from: chforum on 24 / April / 2013, 21:10:28
What causes  the green cast on crw; cr2 files?
What it looks like depends entirely on the software you are using to process or view it. Since CHDK raw is just a framebuffer dump without white balance information, it will generally not look "right" by default in any software.
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How would you go about in best correcting? Set to auto wb?
Camera white balance has no effect on raw data. The best way to correct it will depend on what software you are using. Most raw software should have white balance options.

DNG records the whitebalance setting, which lets your raw software do the right thing when it loads, although the calibration will vary between camera models.
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