About a week ago, Sony announced that the A7RII and the A7SII will gain the ability to record uncompressed 14-bit RAW still images. This is a change vs. the previous ability to record only compressed RAW files at 14 bits.
DPreview did a thorough analysis on the difference between those two options and sure enough there are two significant factors to be considered.
The good news
The first thing that DP review realized is that removing compression from the RAW files obliviated some micro artifacts that were present when the camera compressed the RAW files.
They also have an explanation for it:
Sony’s Raw compression then has a second stage, where the image is divided up into a series of 16 pixel stripes for each color channel. Rather than recording a separate value for each of these pixels, the Sony system records the brightest and darkest value in each stripe, and a series of simple notes about how all the other pixels vary from those extremes. These notes are recorded using fewer bits than it would take to record the actual pixel values and it’s this step that appears to cause most of the problems.
When there’s not much difference between the brightest and darkest pixel, the system is able to describe the scene pretty well. However, as soon as you have a big gap between bright and dark, then the 7-bit values used to note the differences of the individual pixels aren’t sufficient to precisely describe the original image information
The bad news
Of course, not compressing the files means that they are bigger. How much bigger? Twice as big. If a compressed 14bit RAW file weighs around 40.7MB, it uncompressed cousin will weigh about 81.4MB. This, of course has some impact on the number of images you can store on a single card.
It will also have an effect on continuous shooting. Not on the pace of shooting (if anything I would expect the lack of processing to increase the speed) but on the time it takes the buffer to clear the bigger files. That means that each burst will be able to hold fewer photos.
DPR speculates that Sony is yet to provide a lossless compression mode because of limitations with some camera processors, but they did not take this option of the table.
DP review promises to have an in depth follow up on images quality so stay tuned.
[What difference does it make? Sony uncompressed Raw | DP review]