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Questions about RAW images and shooting

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Questions about RAW images and shooting
« on: 09 / April / 2008, 17:23:58 »
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Hello everyone,
I'm a newbie here.

I have CANON S5 which has a maximum resolution of 8Mpixels.

When i shoot RAW images (using CHDK ofcourse) i get files sized 10Mbytes.
Now i know that the pixel depth is 24bit (probably because - 8 bit assigned each color channel), so i would expect to get a file size of 24Mbytes, if it's truly uncompressed.
I guess that i miss something here so i'll be happy if you can explain it :)

Second question,
I understand that the RAW images are linear (gamma=1), and the camera tranfers the sensor data AS-IS to the CRW file. No WB or color transformations being performed.  Right?
So when i convert those to JPG (with 100% quality ofcourse) of TIF, i should apply the color balance myself (and apply  gamma 1.8) or to get the WB data and gamma from the matching JPG file.

Re: Questions about RAW images and shooting
« Reply #1 on: 09 / April / 2008, 17:27:36 »
oops... the 8) "ate" part of my text...
i ment in the last paragraph to apply 1.8 gamma by myself.

And another question about getting the WB and gamma from the matching JPG.
I saw the thread in the forum.
Are there more programs out there that do that automatically? :)
(I mean to drag and drop the CRW and the JPG and get the result to a third, uncompressed, file)

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Offline DataGhost

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Re: Questions about RAW images and shooting
« Reply #2 on: 09 / April / 2008, 17:31:46 »
It doesn't have 24-bit sensitivity but 10-bit, hence 10MB instead of 24MB. The pixels on the sensor can't detect R G and B on their own, they can distinguish just one color (R G or B) in 10-bit sensitivity. After shooting the picture, the 24-bit RGB is interpolated from the each pixel and its neighbours. So, the 10MB you're getting is really the complete RAW buffer with the RAW data from the sensor itself, before any postprocessing (except for badpixel mapping and possibly noise reduction).

More information:
Charge-coupled device - Wikipedia, the free encyclopedia
Bayer filter - Wikipedia, the free encyclopedia

Re: Questions about RAW images and shooting
« Reply #3 on: 09 / April / 2008, 19:14:41 »
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« Last Edit: 22 / April / 2008, 17:09:22 by Barney Fife »
[acseven/admin commented out: please refrain from more direct offensive language to any user. FW complaints to me] I felt it imperative to withdraw my TOTAL participation. Nobody has my permission, nor the right, to reinstate MY posts. Make-do with my quoted text in others' replies only. Bye


Re: Questions about RAW images and shooting
« Reply #4 on: 10 / April / 2008, 15:06:02 »
It doesn't have 24-bit sensitivity but 10-bit, hence 10MB instead of 24MB. The pixels on the sensor can't detect R G and B on their own, they can distinguish just one color (R G or B) in 10-bit sensitivity. After shooting the picture, the 24-bit RGB is interpolated from the each pixel and its neighbours. So, the 10MB you're getting is really the complete RAW buffer with the RAW data from the sensor itself, before any postprocessing (except for badpixel mapping and possibly noise reduction).

More information:
Charge-coupled device - Wikipedia, the free encyclopedia
Bayer filter - Wikipedia, the free encyclopedia

Wow! I didn't know that!
I always thought that each of the 8Mpixels is a full fledged RGB pixel...
That means that my true "RGB" pixel resolution is around 2MPixels with 40bit depth for each pixel. (According to Bayer_filter of 2x2 - Thanks for the link!)

That explains why all images i shot at maximum resolution looks soft when 100% cropped, right?
It would look sharp if i half the resolution...

So, if i get it right, the JPG at 8Mpixels inflates and extrapolates the picture to "create" 24bit depth 8Mpixels,
while in fact the true resolution for 100% should be lower. (But keeping the same file size)

And one more thing,
10bit is considered good compared to other Point-And-Shoot cameras?
I know that SLR's come with A/D's of 12 and even 14bits so it's interesting to compare.
I was reading the review of the G9 at Digital Camera Reviews and News: Digital Photography Review: Forums, Glossary,
        FAQ
and it states that the size of the RAW images is 12.5Mbytes,
which gives for the G9's 12Mpixel resolution a bit-depth of approximately only 8bit per pixel! Could it be?

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Offline vit40

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Re: Questions about RAW images and shooting
« Reply #5 on: 11 / April / 2008, 07:55:33 »
G9 raw files are losslessly compressed, so thay are smaller. CHDK raw files are not compressed

 

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