Posted by John Vaughan on November 11, 2009 at 9:40 PM
Hi All, I'm confused about the compressed format for my RAW files. I have heard of "lossless compression but don't understand how it is possible to compress a file without data loss. Also when I open the RAW image in PS4 is it automatically decompressed? I'm using the type ll AdobeRGB colorspace for the expanded gamut. It's obvious that I am really new to the digital world so if these questions sound simple please bear with me.
Thanks in advance for any help!
John Vaughan
John Vaughan Photography
www.johnvaughan-photography.com
Posted by Rudy Ruberti on November 12, 2009 at 7:25 PM
John,
My Nikon has a menu for setting the compression for RAW files to Lossless Compressed, Compressed, and Non-Compressed. The Lossless Compressed and Compressed modes reduce the file size by 20 to 40% and 40 to 55%, respectively, allowing more images to be stored on the memory card. The Lossless Compressed and Compressed modes use non-reversible and reversible algorithms, respectively, to compress the image (not that I know what any of that means). I believe the bottom line is Lossless Compressed is not supposed to have any effect on image quality and Compressed has “almost no effect on image quality “ (at least according to my manual). Non-compressed does what it says and applies no image compression (no loss of image quality), and results in larger file size. I usually use non-compressed or lossless, depending on what and where I shot. Hope this helps.
Posted by David Bostedo on November 12, 2009 at 8:43 PM
Here's a quicky explanation of lossless compression. Say you had a file where a line of binary data looked like this :
00000000111111110000000011111111
You could instead store that information as :
80818081
meaning 8 zeros, then 8 ones, then 8 zeros, then 8 ones. The "compressed" storage only took 8 characters, where the "uncompressed" took 32 characters. The data doesn't change though, and can be uncompressed to exactly what it was originally.
To answer your other questions, yes, the files are uncompressed automatically by any program capable of reading them. As far as the gamut goes, a RAW file doesn't really have a colorspace until it is processed. So in your ACR in CS4, you choose which colorspace to target the output file at. Your camera setting is ignored. (The same is true for white balance.)
If you want to learn a lot fairly quickly about digital photography, and photography in general, I highly recommend all of the tutorials on The Cambridge in Colour Tutorials Page
Posted by John Vaughan on November 13, 2009 at 12:45 AM
Thanks for the help! I appreciate the links and the explanation of compressed data. It helps to clarify what I am attempting to do and that; of course; is to take the best pictures that I am capable of producing.
Discussion
3 repliesThanks in advance for any help!
John Vaughan
John Vaughan Photography
www.johnvaughan-photography.com
My Nikon has a menu for setting the compression for RAW files to Lossless Compressed, Compressed, and Non-Compressed. The Lossless Compressed and Compressed modes reduce the file size by 20 to 40% and 40 to 55%, respectively, allowing more images to be stored on the memory card. The Lossless Compressed and Compressed modes use non-reversible and reversible algorithms, respectively, to compress the image (not that I know what any of that means). I believe the bottom line is Lossless Compressed is not supposed to have any effect on image quality and Compressed has “almost no effect on image quality “ (at least according to my manual). Non-compressed does what it says and applies no image compression (no loss of image quality), and results in larger file size. I usually use non-compressed or lossless, depending on what and where I shot. Hope this helps.
00000000111111110000000011111111
You could instead store that information as :
80818081
meaning 8 zeros, then 8 ones, then 8 zeros, then 8 ones. The "compressed" storage only took 8 characters, where the "uncompressed" took 32 characters. The data doesn't change though, and can be uncompressed to exactly what it was originally.
To answer your other questions, yes, the files are uncompressed automatically by any program capable of reading them. As far as the gamut goes, a RAW file doesn't really have a colorspace until it is processed. So in your ACR in CS4, you choose which colorspace to target the output file at. Your camera setting is ignored. (The same is true for white balance.)
If you want to learn a lot fairly quickly about digital photography, and photography in general, I highly recommend all of the tutorials on The Cambridge in Colour Tutorials Page
Regards,
John Vaughan