Step-by-step through a CLUT...
Step-by-step through a CLUT...
- Subject: Step-by-step through a CLUT...
- From: tom lianza <email@hidden>
- Date: Thu, 18 Oct 2007 07:47:45 -0400
Hi Ken,
You wrote:
<
Bear in mind that the interpolation method has nothing to do with "building"
the CLUT. This point had me confused for some time when I was starting.
Certainly, interpolation has everything to do with building the CLUT, so I must be misinterpreting your meaning. This interpolation issue has been one of the biggest issues in building profiles since the inception of the concept. You can easily build a target that outputs in uniform grid of %dot, or linear RGB, but the resultant measured data that needs to be projected into the PCS is very non-linear. The data must then be re-interpolated to provide for even-grid spacing in the PCS and this is very challenging. This need for re-griding the data is what started the "dumb" CMM movement, vs the "smart" CMM movement. In the early days (mid 80's), these numeric transforms and interpolations took a great deal of time. Even today, with all our computing power, computing a CLUT from experimentally measured data, can take quite a bit of time. When you couple that with the issues surrounding gamut mapping, the interpolation is extremely complex. In many cases, there is a need for human visual intervention as we approach the endpoints of the gamut of an output device. Many devices behave very badly in very saturated colors (the infamous "hue" hooks) which result in a function that is not directly invertible. The whole goal of this process is to build a profile that can be used with a standard fixed interpolation method for output.
Regards,
Tom Lianza
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