Megabytes per Megapixel (MB per MP)

[Entropy512 (Andy Dodd)]

@Colin_Adams

I think you should mulitply by 16 bits rather than 14. Otherwise you are implying that bits of a pciture element can be shared in a byte. ?This would be a form of compression.

It is possible to bitpack raw data (in DNG parlance, BitsPerSample not a multiple of 8), but in the vast majority of implementations I’ve seen, things get padded up to 16 bits because it’s so much simpler implementation-wise. Interestingly, I’ve experimented with DNGs with BPS of 10 or 12, and Lightroom chokes on those but RawTherapee does not.

Sony definitely stores 14-bit samplies as uint16. So uncompressed Sonys have 2 bytes per pixel plus a little extra for the JPEG preview and a tiny amount for headers and metadata.

Sony’s lossy compression was a fairly fixed mechanism that was constant-ratio - 1 byte per pixel

Lossless compression typically achieves around 1.5:1 to 2:1 ratios depending on content, so 1-1.5 bytes/pixels is typical. A black frame or clipped all-white frame will compress better and may be smaller.

@mbs

One thing to keep in mind is that 7zip, which runs on a regular CPU, can spend tons of effort (and a significant amount of time) obtaining every last bit of compression. A camera, on the other hand, needs to compress each image in a fraction of a second while running on a small battery. It’s very likely that Sony and Canon engineers made different choices when balancing frame rate, time to clear a full buffer, battery life and storage size.

This is why Sony didn’t offer lossless compression until the BIONZ XR.