The key to Masking anything in Photoshop to make an extraction or to replace the background or just change the color of the background is to begin in the channels section. You want to find the channel which gives the most amount of contrast between the subject and the background. If either of the red, blue or green channels don’t offer the most amount of contrast, then creating a new Alpha channel is your best bet.
Every image is different, so naturally a technique which works for one image, may not necessarily work for another. In most situations, though, it’s just a case of modifying your available tools and techniques to get the best results for your specific needs. The important part is to be able to understand why and what each technique is best used for.
Layer masks are best made from a layer or channel which offers the most amount of contrast between the subject that you are extracting or masking, and the background that you are changing or replacing.
In this example I take an image which was shot on a black background of a model with light-colored hair which did provide a fair amount of contrast. Although some of the light spilled onto the background causing an unwanted gradient of black to dark grey. I wanted to replace the background with a solid color. Keep in mind whenever you change the background, it is best to choose a replacement which has a similar luminosity to your original, as the further you get from being similar, the more apparent the extraction or masking will be. For example, if I had replaced this black background with white, the mask edge would have been visible. It is possible to switch from light to dark or dark to light, however, that requires much more time spent refining your mask edge.
After looking in the channels pallet at my Red, Blue and Green channels, and after looking at the RGB channel, I knew that I could make a new Alpha channel combining 2 channels and using a blend mode which would give me a new channel that had a far more extreme contrast than what was available. I decided to duplicate my background layer, convert it to black and white, and boost the contrast between the black and the white before I used an image adjustment of calculations to produce a new Alpha channel, which was the final channel that I used to make a mask from. Sounds complicated? It’s not. Just keep in mind that masks are black and white, with no color, so making a new layer and converting to black and white seemed like a logical solution to boosting my contrast. The native Dodge and Burn tools available in the Photoshop toolbox, combined with some Level’s adjustment was the only tools I needed to work with black and white.
Watch this 10 min video of how I created a near perfect mask in under 5 minutes
The exact same technique can be applied with a few modifications to just about any image that has a good foundation of contrast, whether the background is black, white, patterned or colored. The concepts are the same, the key is utilizing the toolbox to be the most effective for your situation. If you can understand how the tools work, then you can easily modify the technique that I used in your own workflow. I have used the exact technique on an image with a middle color background on a dark-haired model and replaced the background with white and the mask edge was completely undetectable to the point where zoomed at 300% the mask edge was undetectable.
There will be more videos coming in the future dealing with similar masking solutions for various situations, so Please Subscribe to my blog if you’d like to be informed as they become available. Feel free to ask any questions or comment as well. Thanks for the read…Happy Masking!