Re: [Lcms-user] Lab to RGB conversion

[<mar...@li...>]

Hi,

It seems to me that this code is reading the lab pixelss from the file format,
doing some math on floating point with those values and then filling a  
cmsCIELab
structure, which is also floating point. Then it performs a color transform to
convert to RGB 8.

You can do that in this way but is extremly inefficient. Rather, I would
investigate how the file format stores Lab in 8 and 16 bits and convert it
to Lab16 V4 ICC format, which is documented in ICC spec and Lcms manual.
You don´t need floats at all to do this. Then doing the color transform from
Lab16 The throughput gain can be times x4 or more.

Hope that helps
Marti

Quoting Aaron Boxer <bo...@gm...>:

> Hello!
> This isn't strictly an lcms question, but I was wondering if anyone here
> can give me some insight into a few lines of code I've inherited in my
> project that use
> lcms to convert Lab to RGB:
>
> https://github.com/GrokImageCompression/grok/blob/master/src/bin/common/color.cpp#L742
>
> This code works for 8 bit Lab but not for 16 bit and I am trying to fix
> this. I am particularly wondering about the three constants 100, 170 and
> 200.
>
> Any insight would be greatly appreciated.
> Thanks!
> Aaron