Blue Spill Spression


Blue Spill is where light coming from the blue screen washes across areas of the FG.

The idea of surpession is to make that light look more grey than blue.  You do this by desaturating the bluest parts of the FG in a similar way of manipulating the channels with other channels.

Note that you can right-click this image and save the .PSD file that I created when I did the Blue Screen Extract from the previous lesson.  You can use this to start from there for this lesson.

Original image with the Blue Screen Extraction already done

0) Overview: First consider the areas that have blue spill: in the Red Channel, those areas are particularly dark, but in the Blue Channel, the same areas are light, and the Green Channel is somewhere inbetween.  The blue spill areas contain no red information, but spill over somewhat into green [but not as much as the Blue Channel itself.]  We will use the Green channel to bring down the Blue Channel and bring up the Red Channel, and thus bring the spill areas closer to a neutral grey area.  [This is not the best image to illusrate this because it's so dark, but you can still notice it.]


Blue spill on the red Channel
Blue spill in the Green Channel
Blue spill in the Blue Channel

1) Lighten the Red Channel with the Green Channel using Image --> Calculations
Note that this is done on the copy that you have masked off using the Blue Spill Suppression
Use Calculations to Lighten the Red Channel with the Green Channel
See how the major things that change are the blue areas?  And that little else changes in the image?  [Ignore that the BG comes back -- that's okay because it's masked out anyway.]
Compare the Calculations
Rename the new channel -- this is a GOOD HABIT to get into!!  You will quickly get lost in a sea of channels!  [Pun intended! :) ]
Rename the new channel

3) Darken the Blue Channel with the Green Channel using Image --> Calculations
Note that this is done on the copy that you have masked off using the Blue Spill Suppression
Use Calculations to *Darken* the Blue Channel with the Green Channel
See here too, how the blue areas get darker, but the rest stays [for the most aprt] the same.
Compare the Calculations
Rename the new channel -- again, this is a GOOD HABIT to get into!!  You will quickly drown in an ocean of channels!
[Paying attention? :) ] ]
Rename the new channel

4) Now copy the new lightened red into the Red Channel
First, copy the lightened red channel.  Make sure it's selected, then Select --> All [or CTRL-A] and Copy [Edit-->Copy or CTRL-C]
Make sure the lightened red channel is selected for the copy
Then paste into the Red Channel [Edit-->Paste or CTRL-V]
Make sure just the Red Channel si selected

5) Similarly, copy the new darkened blue into the Blue Channel
Copy the darkened blue channel.  Make sure it's selected, then Select --> All [or CTRL-A] and Copy [Edit-->Copy or CTRL-C]
Make sure the darkened blue channel is selected for the copy
Then paste into the Blue Channel [Edit-->Paste or CTRL-V]
Make sure just the Blue Channel si selected

6) This is how it should look
You can see how all that blue has been desaturated and now looks like dark, grey stormy water, while the rest of the colors in the image remain pretty much the same.

The completed image!