[argyllcms] Re: Dispcal and black point

  • From: "Marco N." <manold@xxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 13 Aug 2010 18:11:11 +0200

Thank you for the explanation. 

At this point I think that it is better to use the black offset control offered 
by my Lacie 324 to keep the video LUT less stressed. There is a recommended way 
to set them?

Marco




Il giorno 13/ago/2010, alle ore 02.15, Graeme Gill ha scritto:

> Marco N. wrote:
>> On my NVIDIA GeForce 7300 GT I can't set the black point to 0 (native). 
>> Dispcal seems ignore the -k0 -A1 -f0 settings and it correct always the 
>> three gamma curve of the LUT.
>> http://lh5.ggpht.com/_Ogy3SF4bQ9Q/TGQ9niAuPKI/AAAAAAAAAIk/jzWMEBz18P4/s144/1.png
>> Is it a bug?
> 
> No it's a feature!
> 
> A calibrated display should have a progressive response.
> This means that from 0 giving the minimum output, it should
> start to change as soon as you change the input.
> 
> If a display native response has a "dead band" where nothing changes
> as you change the input, then this results in a vertical jump
> in the calibration curve.
> 
> So the curve you see indicates that your display doesn't change its
> output until it gets (about) 5 as in input, so the calibration curve
> starts at (about) 5, so as to give a progressive response.
> 
> Graeme Gill.
> 


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