Talk:Raw image format

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I merged the "CCD-RAW" and "RAW image file" articles to create this one, and added some new text that corrects some errors in the previous versions (particularly in RAW image file). It can still use a lot of work; I don't know when I'll get a chance, so if someone else wants to contribute please do.

The color depth bullet is probably still confusing. Raw files have 12 bits per pixel, but only one channel (each pixel is either red, green, or blue depending on what color in the Bayer filter covered it. JPEG files have 8 bits per pixel for each channel (red, green, blue), so a total of 24 bits per pixel. But it's difficult to compare color depth between a 1 channel and a 3 channel image. I don't know if this needs to be explained here, in the color depth article, or not. If someone can explain this better, I'd appreciate it. If this is really confusing, let me know and I'll work on it.

A couple of new topics that might be useful:

  • When NOT to use raw; a lot of people are very vocal about it being a waste of time: "shoot correctly and you don't need it"
  • A list of common conversion programs (e.g., Capture-One, BreezeBrowser, Bibble, Photoshop CS and Elements 3)
  • A list of file extensions for common raw formats (e.g., Canon uses CRW, Nikon uses NEF) (the German version has an incomplete list for starters)
  • Some raw formats include an embedded JPEG, I think for quick extraction to evaluate overall quality before making the effort for a quality raw conversion; I don't know whether this is universal or why it is really used so didn't include it
  • More than just a pointer to Adobe DNG, although this could wait a few years to see how well it is received

--Rick Sidwell 20:45, 10 Dec 2004 (UTC)

"Raw files have 12 bits per pixel, but only one channel (each pixel is either red, green, or blue depending on what color in the Bayer filter covered it. JPEG files have 8 bits per pixel for each channel (red, green, blue), so a total of 24 bits per pixel."
That is interesting I would like to see that in the article, about how each pixel is a certain color due to the physical sensor having R, G, and B sensors.
I will try to add mosaicing to the article. However the quality of JPEG vrs Raw is simply untrue. JPEG is not RGB. Each RAW pixel contains 12 bits of brightness information. Whereas JPEG includes only 8 bits of brightness information. Color and saturation are (depending on the parameters) stored at considerably lower resolution. Therefore a RAW image will always have sharper brightness details than a jpeg even if they were both from a better external source. This is a crude simplification of JPEG btw. In reality it is more of a mosaic itself with colors and brightness gradients defined at intervals. --Darkfred Talk to me 21:48, 17 July 2006 (UTC)

[edit] Conversion

Can raw files be losslessly converted to PNG? TIFF? dbenbenn | talk 15:09, 20 July 2005 (UTC)

I don't think the conversion would be reversable, and a certain amount of information would be lost.
You can to a perfect bit-for-bit lossless conversion to Adobe DNG, which is an unusual type of TIFF. With PNG and normal TIFF, you only lose from round-off error and from the loss of little odds and ends like knowing the alignment of the pixels to the camera sensor. It's not like going to a GIF or a low-quality JPEG. --anonymous
But the conversion is still not reversable from .DNG, simply because the digital development settings (contrast, color, curves) are not replicated 1:1 between adobe raw and the various manufacturers conversion utilities. There might be other information changes, I don't know if .dng supports the full range of bit depths that various manufacturers have. .DNG attempts to be a simple unified format whereas the manufacturers each have specific quirks in what data is saved and how it is stored. --Darkfred Talk to me 15:13, 13 April 2006 (UTC)
Oh no. Optionally, Adobe DNG can cheat. It can store all the unrecognized and unconvertable parts of the original file as a great big arbitrary blob. When you convert back, the original can be reconstructed bit-for-bit. AlbertCahalan 04:49, 16 April 2006 (UTC)

[edit] (However, overexposed areas are just as white with 12 bits as with 8, so using raw is not a substitute for correct exposure.)

This is not entirely true. Most blown out areas are only blown out in one or two channels. Adobe's latest version of camera raw software can recover a brightness value from these channels, that is quite realistic, and mix this with the color values from nearby pixels to produce nearly perfect recovery of some highlights. (i have used it to recover entire faces correctly). --Darkfred Talk to me 11:50, 22 September 2005 (UTC)

[edit] Accuracy

I have tried to make the article more accurate by explaining the mosaicing process and changing the comparison with JPEG to relate to how JPEG is actually stored. (previous editor was confusing JPEG with uncompressed RGB, and confusing mosaiced 12bit RAW with 36bit RGB). My grammer is not the best, feel free to make it more readable. --Darkfred Talk to me 22:24, 17 July 2006 (UTC)

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