Trying to understand RAW file formats

R
Posted By
Roger
May 29, 2008
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332
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I am struggling, trying to understand the format of RAW files. I understand that there is a luminosity channel (12 or 14 bits, depending on the camera) for each pixel which accounts for the bulk of the information, plus color information(???).

Here I thought there would just be three 12-bit (or 14 bit) for each color channel but, for an 8 MP camera, this would result in a 36MB (1.5 bytes * 3 * 8 *10^6) file which is certainly not the case (even considering benefit from any loss-less compression). How can Canon fit an 8MP color RAW image into an ~8MB file? Are there really only 8MB/3 = 2.67MP (real, multi-colored MP’s) from a "8MP" camera such as the 20D or 30D?
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T
Tak
May 29, 2008
"Roger" wrote in message
I am struggling, trying to understand the format of RAW files. I understand that there is a luminosity channel (12 or 14 bits, depending on the camera) for each pixel which accounts for the bulk of the information, plus color information(???).

Here I thought there would just be three 12-bit (or 14 bit) for each color channel but, for an 8 MP camera, this would result in a 36MB (1.5 bytes * 3 * 8 *10^6) file which is certainly not the case (even considering benefit from any loss-less compression). How can Canon fit an 8MP color RAW image into an ~8MB file? Are there really only 8MB/3 = 2.67MP (real, multi-colored MP’s) from a "8MP" camera such as the 20D or 30D?

In most sensors each pixel is one of a red, green, or blue. They are are arranged in a matrix using some pattern. When the RAW file is processed an interpolation takes place between neighboring pixels such that the result is pixels which are tri-color, and usually of 8 bits per color.

See the wikipedia article here:

http://en.wikipedia.org/wiki/Color_filter_array

I think most sensors use the Bayer matrix.
JS
Jonas Siebert
Jun 5, 2008
Roger schrieb:
I am struggling, trying to understand the format of RAW files. I understand that there is a luminosity channel (12 or 14 bits, depending on the camera) for each pixel which accounts for the bulk of the information, plus color information(???).

Here I thought there would just be three 12-bit (or 14 bit) for each color channel but, for an 8 MP camera, this would result in a 36MB (1.5 bytes * 3 * 8 *10^6) file which is certainly not the case (even considering benefit from any loss-less compression). How can Canon fit an 8MP color RAW image into an ~8MB file? Are there really only 8MB/3 = 2.67MP (real, multi-colored MP’s) from a "8MP" camera such as the 20D or 30D?

thats out of my imagination….

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