Re: [Openexr-devel] 8 bit int?

[Florian Kainz]

A couple of random thoughts: compression should not be a problem - existing
methods could either be specialized for 8 bits, or the 8-bit data could be
padded to 16 bits.

One problem that needs to be solved is how the mapping between floating-point
numbers and integers gets encoded.  During file reads the library automatically
converts between pixel formats; to do this correctly, the libray must know
about the mapping.  And of course, application code must know about this too.
Your mail suggests that this mapping should be selectable per channel.

I am not sure that "256 levels are more than enough" for masks. If a mask
with a smooth and not very steep gradient is used to interpolate between
two layers that contain essentially flat fields, the stair steps in the
mask can become visible.

> "Use fp16 with piz, it compresses as well as 8 bit" -> on disk, maybe,
> but it takes up twice the space in an in-memory tile cache.

You could read each tile into a temporary buffer and convert the pixels
to 8 bits during the transfer from the buffer to the tile cache.  (Yes, I
know it's not the most efficient method ever, but you can do it without
waiting for an 8-bit EXR data type.)