On Monday 07 February 2005 20:36, Daniel Phillips wrote: > On Monday 07 February 2005 11:21, Lourens Veen wrote: > > Oh, and a remark: I just checked and nVidia's 16-bit framebuffer > > format (which is also used in OpenEXR, that's where I checked) uses 1 > > sign bit, 5 bits exponent and 10 bits mantissa. This almost-13-bit > > reciprocal will probably also be good enough for a floating point > > (High Dynamic Range) framebuffer... > > I have strong doubts that 13 bits is enough precision for the > reciprocal. I think 16 bits is barely enough. I'm not in a position > to quantify that yet, though.
Attached are two renders (I made the quad's angle a bit more extreme) of the software model. One is with float25 and correct division (16 bit), the other is with float25 and the approximate reciprocal (a little less than 13 bit). There are a few off-by-one errors, but to my naked (well, I wear glasses) eye there is no difference. Judge for yourself. Tips for better tests are welcome by the way, I have no idea whether this is worst case. Lourens
<<attachment: textured_image_float25_approx.png>>
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