Re: [APML] Channel percentages in PS

[Chuck Vaughn <aa6g@aa6g.org>]

Jason,

I'm not sure if this is exactly what you're asking but I'll pass this 
along anyway.

If you have CCD linear data and let's say you've made 3 equal exposures 
for RGB and the exposures should be something other than 1:1:1, select 
the most under exposed channel as the reference, and use PS Curves to 
reduce the white end of the other two channels by the percentage they 
are over exposed. This will work if the data is not saturated. I use 
this technique on the Mars Rover images where the G & B images are over 
exposed and a similar technique on weather satellite images where the 
RGB channel data lies in different segments of the linear response 
curve of the sensors.

You can also go in the other direction if there's enough linear range 
left at the top end of the channels.

It's very hard to do this with film since it is non-linear. I did it 
with my tricolor TP images but I ran one test and then stuck to ratios 
between channels so I could adjust Curves the same every time. If I 
varied the exposure ratios I would not have known how to adjust them.

Chuck

----------------------------------------------

>
>
> Robert Gendler wrote:
>>
>> significantly I experimented with different ratios, ending up with
>> 1.3:.0.9:1.0
>> for the RGB.
>
>
> Is there an easy way to do this in Photoshop, that is simply
> change the percentage of the R, G, or B? I know you are
> doing this when you muck with curves or levels but that's
> non-linear because you are having to work with black/white
> and mid set points. I just want to do something like
> RGB = 0.5,1,1
>
> -- 
>  -Jason Ware 

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