How Exactly does teh Color Cast Removal work

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norris_watkins
SilverFast Beginner
Posts: 20
Joined: Mon Nov 07, 2011 8:16 pm
Scanner: Epson V700
SilverFast Product: SE Plus

How Exactly does teh Color Cast Removal work

Postby norris_watkins » Thu Jan 19, 2012 4:44 am

( Im using Silverfast Plus 8.0 on an Epson v700 scanner )
I would like to know how Color Cast Removal tool ( under Histogram ) works.
When I click it, I see Shadow and Highlight sliders moving
Actually they moved by different amounts for each color channels ( So it is definitely doing some color shift )
But I see a lot of clipping looking at the histogram ( Lot of areas outside shadow and highlight sliders ). I thought this is very bad as you are losing details in teh highlight and shadow area. But yet looking at teh picture, it doesnt look that bad at all. In fact it seems to have removed teh color cast somewhat.
1. Do I really lose details if I enable Color Cast Removal ?
2. How does Silverfast know, which area of the picture is white ( How else does it find out which color should be reduced )

LSI_Morales
SilverFast Master
SilverFast Master
Posts: 1430
Joined: Mon Oct 22, 2007 9:33 am

Re: How Exactly does teh Color Cast Removal work

Postby LSI_Morales » Wed Jan 25, 2012 12:13 pm

Hi there

norris_watkins wrote:I would like to know how Color Cast Removal tool ( under Histogram ) works.
When I click it, I see Shadow and Highlight sliders moving
Actually they moved by different amounts for each color channels ( So it is definitely doing some color shift )


Color Cast Removal finds and sets the darkest and lightest points of each color channel independently. The next pictures illustrate this, red and green channels are relatively similar, hence you do not see a big difference, notice however the blue channel. See how the limits differ from channel to channel.

Red_Channel.png
Red_Channel.png (28.09 KiB) Viewed 1754 times

Green_Channel.png
Green_Channel.png (28.32 KiB) Viewed 1754 times

Blue_Channel.png
Blue_Channel.png (28.96 KiB) Viewed 1754 times


norris_watkins wrote:But I see a lot of clipping looking at the histogram ( Lot of areas outside shadow and highlight sliders ). I thought this is very bad as you are losing details in teh highlight and shadow area. But yet looking at teh picture, it doesnt look that bad at all. In fact it seems to have removed teh color cast somewhat.
1. Do I really lose details if I enable Color Cast Removal ?


As seen in the previous pictures there is in fact a small amount of pixels left out the limits.
SilverFast has a shadow and highlights threshold, this is a sort of security feature to avoid having dust, scratches on the film or scanner glass itself or damaged pixels of the ccd affect the image correction.

norris_watkins wrote:2. How does Silverfast know, which area of the picture is white ( How else does it find out which color should be reduced )


By setting the limits on each channel individually.

Kind regards
Alejandro Morales

LaserSoft Imaging
Media manager, Software testing


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