Masking with Channels
Source: Planet Photoshop: Masking with Channels by Corey Barker (video)
My orginal image and extracted masked image - I've used a blue background so the masking shows up better.
Here is a low-res snow photo from the web that I tried to use this technique on and had better results. Results are still not as good as the tutorial but with practice it can be perfected and as Corey says it is less time consuming than trying any of the other masking tools which don't work in this type of situation. I did find when trying to locate test photos the background has to have a simple background.
This is my attempt to provide a transcript of the video clip that will allow us to complete the task without having to keep returning to the video for instruction.
How to mask for complex images with simple backgrounds. The video shows a snow boarder in the air with lots of small flakes of snow scattered all over that he want to keep.
Go to windows and ensure Channels is open.
You edit in an alpha channel so it is done visually. Extracting hard to get parts of the photo. Most standard selection tools won't work.
Open Channels and find the most contrasting to the subject and the background -RGB channels. For an alpha channel you need it to be straight black and white but inevitably end up with grey.
Black will be the unselected area and white the selected area.
Toggle to the selected channel and we are going to use a feature of PS that most people ignore or are afraid of because of the complicated menu. Go to image menu and select Calculations. We are going to uses calculation to darken up the grey areas. There are three sections. The Source will stay the same, as we want it to apply to the image we are working on. The Layer will be the background and the channel will be the channel we selected with the most contrast and the blending will be Multiply to change the background from grey to black. The result will be a new channel. Click OK and in your channels there will be a new channel called Alpha 1.
Now invert the alpha1 channel Cmd + I to make it easier to work with.
Now press Shift Delete - go into the fill window in use Black and in the Blending area set it to Overlay. What this will do is ignore white area and other areas will be forced to black. It can be done a second time if necessary.
Select the brush tool small brush, hard edge and change blend mode on the brush tool to Overlay. then we can paint with black in the area. There may some areas that are too light and you will not be able to paint them. When that happens you can change the brush blend mode to normal and paint - be careful as now the brush will paint on the white areas.
In the alpha channel any area that is white is going to be your selection and grey partially selected and black unselected. So we want to invert the image again Cmd + I. It was easier to paint with black and define the edges is why the image was originally inverted.
The background area may still have some grey in it. Use levels to move the dark slider in to make it black and click OK on the curves. Now ready to extract. Go to layer panel.
Unlock the background layer - drag padlock to trash. Go to Select and Load Selection loadsthe alpha channel as a new selection and click OK. Click the layer mask icon at the bottom of the layers.
To see how good the selection is add a new layer underneath and give it a fill colour. It should be nicely extracted. You may have to do some fine tweaking using the paintbrush in normal mode black background to clean up some areas.
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