#CHROMA KEY PLUGIN PHOTOSHOP HOW TO#
#CHROMA KEY PLUGIN PHOTOSHOP PROFESSIONAL#

The process: The green can be turned to transparency by applying Colors > Color to Alpha. To stay in truth your colored stripes would be recovered quite well with the next process because the programmer has thought in same way as you - like the unwanted color is there only due transparency. You need something much more advanced than GIMP if you want some guessing ability. It sees only the mixing result pixel by pixel with no idea what kind of common creation process could be behind different pixels. Actually you didn't guess, you constructed the stripes that way, but a dumb automate with no AI cleverness cannot know how an image is constructed. In your image of 'what should be done' you guessed that the horizontal color stripes continue with the same hue and saturation, but the transparency increases as the color moves closer to pure green. Unfortunately there's no way to calculate exactly the original color of the mixes areas because we do not know is it mixed due the transparency (= more transparent hairs near the edges) or was it originally with no green background colored to more green at the edges than in the middle of the scalp. Obviously your scalp with green background presents well your problematic images - large areas where the green is mixed with hair:

#CHROMA KEY PLUGIN PHOTOSHOP HOW TO#

Even with the simple function, I understand what it's saying, but I would not know how to perform it using simple selections and channel manipulation.

#CHROMA KEY PLUGIN PHOTOSHOP PROFESSIONAL#

Given all this undefined behaviour in the problem space itself, I'm sure Adobe Premiere and all the other professional video production tools contain very sophisticated chroma keying algorithms.Д¬an we even approximate the result of those algorithms using basic image manipulation, as found in Gimp? Or is any such endeavor bound to fail?ДЄlternatively, is there an open source Gimp plugin or separate program that can perform a good quality chroma keying on pictures?Д®dit: Wikipedia's article gives an example of a simple function for green screen: rgb(r,g,b) -> rgba(r, min(g,b), b, A*(r+b)-B*g) and goes on to explain that modern algorithms can be much more complicated. For instance, the color that lies exactly between the key color (green in this case) and its exact opposite (which would be magenta in this case) is a perfect gray (by definition of opposite color.) Do we need to turn that shade of gray into semi-transparent magenta? What if it was an actual gray in the original picture? (Which is actually more likely.) I don't know the theoretical background behind chroma keying and I'm guessing it could be quite hairy. You can not turn a shade of green into semi-transparent red, and another shade of green into semi-transparent blue, just by fiddling with the magic wand, the color selection tool, or by copying a channel into a mask.

The reason I posted this question is that all other questions and answers about this topic miss this crucial point. Meaning, if the key color is green, all greenish colors need to be substantially modified, in addition to having a suitable alpha channel added: Notice how this procedure is not merely adding an alpha channel it is changing all colors that lie in the same quadrant as the key color itself. If we look at what needs to be done (or approximated as far as possible, see below) it is the following:

(Note: I don't know how to do it yet, this mockup was made starting from a stock transparent picture.) Is it possible to apply chroma keying, meaning to remove a green (or blue.) screen background, using Gimp? (I happen to use Gimp, but I suppose an answer using Photoshop would be just as good, unless it's referencing a specific Photoshop plugin.)

Chroma key plugin photoshop