Compression with RAW


Today’s Question: My camera gives the option of taking pictures in Compressed RAW or Uncompressed RAW.  Since compressed RAW is a smaller file size I see its advantages, but does the compressed file photo lose any capabilities when post processing in Lightroom or Photoshop?

Tim’s Quick Answer: The answer here depends on your specific camera. Some cameras offer lossless compression when they provide a Compressed RAW format, while others use lossy compression. If the RAW capture employs lossy compression, there is a certain degree of risk that some detail or quality will be lost.

More Detail: As most photographers are probably aware, a RAW capture represents (with a few limited exceptions) the capture data exactly as that data (the light) was recorded by the image sensor in your camera.

Other capture formats, such as JPEG or TIFF, involve in-camera processing to take the RAW capture data and convert the information into actual pixel values. One of the advantages of a RAW capture is that you can exercise some additional control during the process of converting the RAW capture to a pixel-based format in post-processing.

Many cameras now offer a compression option for RAW captures, primarily focused on reducing the file size for those captures. This helps to reduce storage usage on the media cards you use when capturing photos, and also reduces the amount of time those RAW captures require to download to your computer or otherwise copy to a different location.

There are a variety of ways compression can be applied to an image file. You can think of lossless compression as simply recording information in a more efficient way. For example, imagine you had a photo with a row of 1,000 pixels that were all the same shade of blue. It would be far more efficient to say “1,000 blue pixels” than to repeatedly say “blue pixel” one thousand times.

Lossy compression does cause some information to be lost. Let’s assume that we modify the example above to involve a row of 1,000 pixels where each pixel is a slightly different shade of blue. With lossy compression you might still say “1,000 blue pixels”, even though each pixel is a slightly different shade of blue. We haven’t lost a huge amount of information, but some information was lost.

With lossy compression for a RAW capture you may lose a slight amount of color fidelity, dynamic range, and smoothness of gradations. In most cases the loss would be so subtle as to be nearly impossible to see without exaggerating the differences using software.

If your camera offers a lossless compression option for RAW captures, I would certainly be in favor of using that option. If the only compression option for your RAW captures is lossy compression, I would acknowledge that the risk to your photos is minimal. However, I personally prefer not to use lossy compression for RAW captures, mostly from a philosophical standpoint. After all, one of the key reasons to use RAW capture in the first place is to preserve as much information as possible in your captures.