Compressing RAW files.

I thought the part of the point of raw files is that they are uncompressed?!
 
The Nikon D800 can record RAW files in Lossless compressed- compressed or uncompressed as shown in that link
 
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odd jim said:
I thought the part of the point of raw files is that they are uncompressed?!
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No. Lossless compression is by definition harmless, so that's fine for raw files. I can't see the point of lossy compression on raw files though.
 
So from that article do I understand correctly that Canon cameras don't allow for any raw file compression, whether lossless or not? :thinking:
 
I can't speak for all Canon cameras but neither of mine offer raw file compression.
 
odd jim said:
I thought the part of the point of raw files is that they are uncompressed?!
Click to expand...
Since the RAW file is simply a collection of data from the sensor diodes I presume that the files could, in some way, be compressed without altering the data in the same way that any documents could be compressed.
 
Nifkin said:
So from that article do I understand correctly that Canon cameras don't allow for any raw file compression, whether lossless or not? :thinking:
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Well, there are three questions here:
  1. What does the article say about Canon cameras?
  2. What did you infer from the article?
  3. What do Canon cameras actually do?
You seem to be asking question 2, but only you know the answer to that. I'll concentrate on question 3, which is the most interesting anyway.

Canon DSLRs don't give you any control over the compression or bit-depth of RAW files. From this we might reasonably surmise that they are not subjected to lossy compression (because otherwise they would surely give you another option) and they are saved with the maximum bit depth the camera can achieve (because otherwise makes no sense).

We can infer more details by comparing file sizes between Canon and Nikon cameras.

Here's the image size chart from a Canon 5D Mark III instruction manual (page 123):
upload_2017-8-22_12-57-14.png

and here's the corresponding chart from the Nikon D750 user's manual (page 492):
upload_2017-8-22_13-3-51.png

The two sensors have very similar resolutions (Canon 22.118 MP , Nikon 24.160 MP), so this suggests to me that the Canon RAW files are 14-bit with lossless compression.
 
StewartR said:
Well, there are three questions here:
  1. What does the article say about Canon cameras?
  2. What did you infer from the article?
  3. What do Canon cameras actually do?
You seem to be asking question 2, but only you know the answer to that. I'll concentrate on question 3, which is the most interesting anyway.
Click to expand...

What I inferred from the article was the following:
Nifkin said:
that Canon cameras don't allow for any raw file compression, whether lossless or not
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...I was stating what I'd inferred, not asking what I'd inferred, so number 2 wasn't my question. I was putting forward my inference to see if I'd understood the article properly, which I suspected I hadn't, and may have been confused by the terminology.

My question was simply to confirm whether I'd understood the matter with regards to Canon or not, and, if not, receive a bit of clarification on what Canon cameras can do: this probably fits with question 3. I wasn't in a position to look at my cameras or their instruction manuals when I posted last night, so was unable to check how Canon cameras handle raw files, whether uncompressed, lossless or lossy compressed.
 
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If you read the DCraw open source .CR2 handler, you can see the file contains some thumbnails and a data block. The data block contains a lossless JPEG YCbCr 4:2:2 image. This seems to be 14 bits stored in 2 bytes?
 
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