Re: bad precision with CMMatchFloatBitmap and CWMatchColors
Re: bad precision with CMMatchFloatBitmap and CWMatchColors
- Subject: Re: bad precision with CMMatchFloatBitmap and CWMatchColors
- From: Klaus Karcher <email@hidden>
- Date: Mon, 29 Dec 2008 16:03:28 +0100
Klaus Karcher wrote:
I've got some weird results using CMMatchFloatBitmap and CWMatchColors
with simple RGB gamma + matrix profiles. [...]
Can someone please have a look at my code an tell me what I'm doing
wrong? Or confirm potential bugs in Apple's ColorSync API?
Here is a second version of my test tool:
<http://digitalproof.info/colorsync-dev/convert2.zip>
It converts a large number of random RGB values and calculates the
average / maximal round trip errors.
These are the results of two test runs:
1.) with "testRGB.icc" (green primary exceeds Lab UInt16 range)
Number of tests: 100000
Delta E avg / max lapack: 0.01 / 0.02
Delta E avg / max float Lab: 1.10 / 9.60
Delta E avg / max fixed: 1.10 / 9.59
Delta E avg / max float XYZ: 4.86 / 33.80
2.) with another profile (gamut well inside UInt16 range)
Rgamma: 2.234375
Ggamma: 2.234375
Bgamma: 2.234375
Red: X: 0.478958, Y: 0.275146, Z: 0.049362
Green: X: 0.350143, Y: 0.618881, Z: 0.130112
Blue: X: 0.135101, Y: 0.105972, Z: 0.105972
Number of tests: 100000
Delta E avg / max lapack: 0.00 / 0.02
Delta E avg / max float Lab: 1.24 / 9.18
Delta E avg / max fixed: 1.25 / 9.18
Delta E avg / max float XYZ: 5.40 / 27.29
... and here some plots of a test run with the second profile.
They show the position of large errors orthogonal to several planes of
the Lab- and device space:
<http://digitalproof.info/colorsync-dev/errorDistribution.pdf>
Klaus
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