[Haskell-cafe] Looking to check on some capabilities of Data.Colour

Jeff Heard jefferson.r.heard at gmail.com
Thu Aug 6 16:02:27 EDT 2009

Excellent.  That's what I wanted to know :-)

On Thu, Aug 6, 2009 at 4:01 PM, <roconnor at theorem.ca> wrote:
> On Thu, 6 Aug 2009, roconnor at theorem.ca wrote:
>> On Thu, 6 Aug 2009, Jeff Heard wrote:
>>> I was wondering if Data.Colour supported Double-valued colour
>>> components > 1.0 or less than 0.  I'm looking to create an HDR image
>>> processing library, and Haskell has one of the most extensive and
>>> correct colour models around, thanks to Russell.  With 16bpcc or
>>> 32bpcc images, however, I need to be sure to be able to correctly
>>> calculate colour values that fall outside the usual [0.0,1.0] gamut.
>>> Does Data.Colour support this functionality?
>> Data.Colour supports values outside the range [0,1] for most computations.
> To be slightly more techinical, I want add that Data.Colour.Colour is
> abstract and its interface cares nothing about [0,1].  Gammut issue only
> arise when converting the abstract data type to and from concrete
> coordinates, and which colours are outside [0,1]*[0,1]*[0,1] is coorinate
> system dependent.  Since Data.Colour.Colour is abstract and coordinate
> system indepenent, it cannot (or at least should not) care about such issues
> for oprations that deal only with abstract colours (operations such as
> blending, etc.)
>> Components are clamped when extracting to Bounded component types such as
>> Word8 (see toSRGBBounded).  There may also some issues with negaive values
>> when converting to non-linear coordinate systems via a transfer function.
>> This is an area I haven't thought to much about, so there could be a few
>> "bugs" lurking here.  If found they should be fixed, assuming "right"
>> behaviour can be found.
>>> -- Jeff
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> --
> Russell O'Connor                                      <http://r6.ca/>
> ``All talk about `theft,''' the general counsel of the American Graphophone
> Company wrote, ``is the merest claptrap, for there exists no property in
> ideas musical, literary or artistic, except as defined by statute.''

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