Datacolor User to User Support Group.

--- In colorvision_group@yahoogroups.com, "Brian Smith" <zen1@...> 
wrote:
> I may be completely wrong here but I think you are getting the 
wrong 
> end of the stick about the purpose of this device. I don't think it 
is 
> ever intended to match the illumination levels between monitors or 
any 
> other viewing system, just give the same appearance of colour. Also 
I 
> think you have the terms a little mixed up. My understanding of 
> brightness, as a control, is that it adds or subtracts a constant 
> value from the value of each pixel but the overall luminance of a 
> pixel depends on the source of the light, be it backlight, CRT 
> phosphor, or 10kW projector lamp. Contrast, as a control, affects 
the 
> steepness of the curve that relates pixel values to screen 
brightness 
> values. It should not affect the black or white point.

If contrast was to control that curve then it should be called Gamma, 
really.... no?
The terms brightness and contrast are confusing, even more when they 
relate to an LCD display. Strictly speaking and since the luminance 
of your display depends partly on your own subjective assesment and 
partly on the amount of ambiant light, these two "knobs" are there to 
allow you to set your pedestal (black level, usualy called 
brightness) and your white point luminance (usualy called contrast). 
This rule applies well on a CRT, as for LCD's I am not so sure.
  
> 
> Again, I may be completely wrong, but I think it is unreasonable to 
> expect to match the actual illumination levels of your monitor and 
> your client's. All you can expect to do is both be able to see the 
> same shadow and highlight detail and perceive the same colours. 

If you can adjust for same shadows and highlights and if you are set 
up for similar gamma, then you will see roughly the same thing, I am 
pretty sure.


> Presumably your client's screen is not the end use for your images. 
If 
> they are going to be ending up as print then the illumination 
levels 
> are meaningless anyway.

Well this is true but if you adjust your pictures for a screen whose 
over all luminance is widely different from the one on which your 
pictures will be seen then your pictures will appear widely too 
bright or dark on that same display, which indeed does not imply 
anything as for further uses. 
>