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A7rII: RAW compressed vs. RAW uncompressed


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I would be interested in other users thought on the question of shooting compressed vs. uncompressed RAW files with the A7rII.

 

I have been shooting uncompressed thus far. I make large exhibition prints. Occasionally for a less important assignment or one with a smaller final output I shoot compressed RAW.

 

I googled this topic when I first got the camera and found a an extreme pixel peeper who had done tests and claimed that, when shooting compressed RAW files, he could see small artifacts in areas where dark and light areas met.

 

Anybody done real world comparisons, making prints etc.?

 

I am traveling in Asia and had to buy a second external drive to accommodate my 85 MB uncompressed RAW files. It sure would be nice to cut my storage needs in half by shooting compressed RAW files, if there were no discernible loss of image quality.

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i tried printing a test chart reshot at both compressed and uncompressed and printed to A3+ (thats the biggest I can print )and could see no difference close up or at a sensible viewing distance.

 

what would happen with a fine art b/w image at larger sizes I dont know but I suspect again if you view from a sensible distance it would ,at best , be minimal.

 

For your trip I would shoot compressed unless it was very dark with lots of shadows you wanted to keep detail in.

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Hi badbluesman,

 

I have no practical experience on the difference you're asking about. But would like to contribute some theoretical aspects:

 

In terms of compression, there is a distinction between lossy and lossless compression. Both types of compression give you some kind of storage space savings.
When retaining the full information is of maximum importance, of course lossless compression is the way to go. And there is only so much compression you can achieve that way, depending on the kind of picture you’re taking. Unfortunately, Sony cameras do not offer you the choice of lossless compression.

In lossy compression, there is theoretically an unlimited amount of storage space that you can trade in for loss of information. Clearly, there is no point in having a 42 Mpix camera when you finally throw away most of the information. Whether a loss of image quality is discernible is purely a matter of how closely you look. Terms like "sensible distance" rather blur that fact, imo.

On the practical side, I can fully understand that each additional piece of equipment (for instance a 2nd external hard disk) is a hassle, especially when travelling. I see several ways to deal with this:

  • Use one bigger disk instaed of two or more small ones. The size/weight difference should be negligible.
  • Send the full disk home while carrying only the one “in progress” around.
  • Selectively shoot at different image sizes, Use maximum resolution only where it matters.
  • Selectively use compression or not.

For the latter, it helps to understand which situations are likely to produce compression-induced artefacts:

 

According to this post by a researcher on image compression, artefacts are most likely to occur in high-DR (dynamic range) scenes shot at low ISO. That's when you probably would want to shoot uncompressed raw.

You may want to give this link a try, if you want to dig deeper into the intricacies of image compression.

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