Sony has just announced that its latest cameras will gain the option to shoot uncompressed Raw files. The move comes in response to user feedback (and, we're told, our efforts to communicate this feedback to the company's senior management), and provides a choice between shooting the with the existing two-stage lossy compression or an uncompressed Raw file. Given the interest that was generated when we detailed the effects of Raw compression, we thought it was equally important to make clear the benefits of the newly-added uncompressed Raw option.

What difference does this make?

When we explained the impact of Sony's compression on Raw files, we said the localized second stage of the compression was the aspect that was most visually destructive and, sure enough, this is where the benefit to shooting uncompressed Raw is seen.

The removal of the localized compression of 16-pixel blocks means the files no longer introduce errors and artefacts around high-contrast edges.

And it's gone: the artefacts present in the compressed Raw file are completely absent in the newly uncompressed files.

We've analysed the uncompressed Raw files and can't find a significant difference in the amount of dynamic range being offered. There's possibly a tiny improvement if you try to brighten very deep shadows but the difference is so subtle that we don't consider it to be photographically significant. But, even without this, the camera's Raw files are more flexible than they were before.

How big are the files?

They're essentially twice the size. The uncompressed Raw files we've shot are consistently around 81.4MB, compared to the ~40.7MB files produced of the same scene using compressed Raw.

What's the effect on continuous shooting?

This is where things become a bit unclear because we aren't able to test continuous shooting. We're told that uncompressed mode doesn't reduce the continuous shooting speed, it just reduces the number of shots that can be taken before the buffer fills.

Are they 14-bit?

Close examination using RawDigger shows that the uncompressed files no longer skip every alternate Raw value: they're true 14-bit files, rather than having 13-bits of data in a 14-bit space.

They certainly appear to be. We used RawDigger to examine the uncompressed files and found that there aren't large numbers of un-used Raw values as was the case before. However, until we can install final firmware on a production camera, we can't test continuous shooting so don't know what the files produced when the camera drops to 12-bit read-out mode will look like.

This is not the end of the story

In our discussions with Sony, the company was keen to stress that it is still listening. We suspect the reason Sony is offering uncompressed Raw, rather than losslessly-compressed Raw that some users would like, stems from the limitations of working with the cameras' existing processors, rather than any misunderstanding about consumer demands. The company says it will continue to listen and will investigate the development of a lossless compression system if there's sufficient user demand.

And, now that we've got access to uncompressed Raw files, we should be able to publish an assessment of image quality, early next week.