.The first color photograph was made in 1861 by James Clark Maxwell (the handsome dude you see to the right). Maxwell studied the human eye to find that our eyes were sensitive only to red, green, and blue light.
Before long, Maxwell had developed a method (now called the Harris Shutter effect) to mimic our eyesight and make color photographs by making three black & white pictures: One with a red filter over his lens, one with a green filter, and one with a blue filter.
When he combined them together, photo magic happened and the color photograph was born!
Let’s play with this!
So now T_Paul at RetouchPRO is proposing a fun challenge: to re-construct a color image from a film roll with 3 different black & white shots that clearly belong to each one of the three RGB channels.
Here’s the process I followed to obtain the following result:
If you would like to have your go, surf over to RetouchPRO’s site.
Aligning the three layers was a bit tricky, because as they are shot in turn they’re not exactly the same. Specially the guy in the middle couldn’t hold it and moved significantly. So I first attempted an automatic alignment (in Photoshop Edit>>Auto-Align Layers) cutting each one of them from the strip and placing them as 3 different layers in a new image.
To adjust minor alignment issues your can play around with opacity to visualise a layer and the one right below. At this point it is sufficient just to be sure the logs, that obviously didn’t move, are pretty straight. We’ll deal with the guys later on.
Rough color correction
I later saved each layer as a different image that would become my red, blue and green filters and loaded them as channels on a new RGB multichannel image (remember: in PS Mode>>RGB).
How to know which is which is merely intuitive. The higher the amount of white, the more of that color you will obtain in the final mix. Therefore faces should be pretty dark in the blue filter, and skies darker for the red filter… and so on. According to this theory, you can instantly recognise what’s going to happen. The red filter is so light that there is going to be far too much red component in the composition.
To roughly compensate the filters let’s apply a level correction to each one of them first:
Further color correct
Several adjustment tone and color calibration layers later, the image looks like this:
[one_half]For a more detailed, zone specific color correction, you can treat each channel separately. By following simple color rules you can manage to change a wrong color only altering 33% of the information in the area. This is a simple RGB color wheel where you can see the three primary colors, together with their secondary colors. If you want to remove a red blemish, you’ll need to go darker on the red, but also perhaps it is a good idea to go lighter on the green layer as it is magenta’s complementary color.[/one_half][one_half_last]
In this particular photograph I dealt with yellow spots due to small aberrations, which I solved by simply painting on the blue filter with white on “lighten” multiplicity mode.
In optics, chromatic aberration is a type of distortion in which there is a failure of a lens to focus all colors to the same convergence point. It manifests itself as “fringes” of color along boundaries that separate dark and bright parts of the image. In our example it is due to movement. Not all three filters overlap exactly the same so you can get fringes of yellow, magenta or cian here and there. In this occasion I corrected it locally by manually adapting the alignment of only the channel that is off. See the results:
A mixture of both techniques, color correction by channel and chromatic aberration adjustment, were used in this guy’s face:
As for image restoration, I had to get rid of all artifacts on the image. Most of them would be due to weathering on either one of the filters, so instead of flattening out and working on a composite image, I preferred to go on and heal each one of them per filter.
As seen above:
- CYAN imperfections are corrected in the RED filter
- YELLOW imperfections are corrected in the BLUE filter, and
- MAGENTA imperfections are corrected in the GREEN filter
And finally, general retouching. And by this I mean to flatten the image and apply levels, toning and, like I did in this case, frequency separation technique to increase definition on the main subject and obscure disturbing details.
Here’s the difference:
Have a go at it yourself and post it to RetouchPRO! Here’s the link: http://www.retouchpro.com/forums/contests/37935-aug-sep-2014-merge-channels-contest.html