[Openexr-devel] LUT for HDR-histograms, too?

[Matthias Biedermann]

Hi there,


I've just looked thru your nifty fragment-program and have two questions
concerning this technique:

1) The pipeline-comment mentions that applying the exposure has to be
limited to rgb only. However, the line "half4 c = h4texRECT (image,
texCoord) * expMult;" does the multiplication to all four components of
the half4, doesn't it? Or have I just missed the details of
"h4texRECT"...?

2) Do you think the same approach (using a 2D-texture as lut indexed by
floats) would work with creating a histogram of the HDR-image? As I need
some information about the "light sources" of the HDR-Envmap, some sort
of image processing (binary/n-ary thresholding) based on the image's
histogram has to be performed beforehand...


Thanks,
Matthias

p.s. just read your additional comment on the lut...so I guess my second
question might be feasible...;-)



> -----Ursprüngliche Nachricht-----
> Von: Drew Hess [mailto:address@hidden 
> Gesendet: Montag, 26. Januar 2004 23:30
> An: Matthias Biedermann
> Cc: 'Billy Biggs'; address@hidden
> Betreff: Re: AW: [Openexr-devel] Missing include - and other 
> questions...
> 
> 
> 
> Hi Matthias,
> 
> If you have a programmable GPU available with support for 
> 16-bit FP pixels, you can do a neat trick with a Cg shader 
> and a 16-bit lookup table.  Assuming you can bake your 
> tonemap into the table and you have the right hardware, this 
> is pretty fast.
> 
> I've attached the Cg shader that does this.
> 
> 
> -dwh-
> 
> 
>