Re: [Openexr-devel] DWA compression

[Sean Y Chen]

I have 0 technical expertise on this algorithm, but perhaps an idea for the slider would be to use it for setting target file size. I don't know if the algorithm allows for this or if that is even practical. In Brendan Bolles's demo video, it seems that 100000 is the limit for a couple of the images, though one of them goes to 250000 before reaching file size 1. Anyways, just ramblings from a musician/amateur coder.

Cheers,

Sean

On Sun, Aug 17, 2014 at 2:07 AM, Larry Gritz <address@hidden> wrote:

The new compression modes are really great, thanks. I've been playing around with it and it performs very well, great compression while retaining visual quality.

But the numbers are confusing. Apologies if I missed prior discussion of this point, but does anybody have an explanation of what the value means?  I understand the basics -- higher is more compressed, below 100 gives nearly perfect visual fidelity -- but maybe because the scale is unbounded and highly nonlinear, I haven't been able to come up with an easy-to-explain description.  In contrast, the 1-100 scale for JPEG quality has a more intuitive feel that, while still not linear, seems to be no trouble to wrap one's mind around (maybe because it reminds us of percentages?) and is much more amenable to putting into a UI slider. I'd love to find an equation that would map an intuitive 0-1 or 0-100 scale inside an app to the dwaCompressionLevel in an analogous way.

--
Larry Gritz
address@hidden




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