Image Masking, 2

Yesterday I showed what a mask is and why it’s important in image editing. Today I’ll continue with the same image and the same editing adjustment – conversion from a color image to a black & white image with a few spots of selective color. This may not be the most common and useful application of masks but serves to illustrate how they work.
All of the images are screen captures so their quality isn’t first rate, but serve to illustrate the topics. Click any image to enlarge it.
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The image on the left is as captured in camera. The image on the right is our destination. The color image was converted to B&W while leaving the green of the pines and the brown of the cattail intact. The total time to accomplish this conversion in Capture NX2 was under two minutes – start to finish – starting with a RAW file. I don’t know how long it would take in Photoshop but suspect it would be much longer. NOTE – PS users, everything demonstrated in this post can be done in PS by means of Nik Software’s Viveza 2 plug-in.

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Masks can be created in many ways – ways that are totally dependent on the capabilities and features of the image editing program. As noted yesterday, not all programs offer masking. In the Adobe family full Photoshop does but Elements and Lightroom do not. Capture NX2, through the use of Nik Software’s U Point technology offers one of the easiest and fastest methods for selectively applying adjustments through masking.
The most rudimentary way to create a mask is by using a standard image editing brush tool. For example we could create the following mask and resulting image (recall that white allows the adjustment and black holds it back) –

Another option for displaying a mask, in the form of an image overlay, is shown in the next pair of images. The only thing different is that I’ve chosen to display the B&W mask from above as an overlay instead. If you choose to create a mask using a brush then some form of overlay display is essential – else how do you know what you are masking?

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Let’s try using a brush to mask out the pine trees.

We can see from this mask overlay that I’ve “colored outside the lines”. One could do better but the required time and effort is extensive – and the pine trees are only moderately complex as compared to the grasses at the bottom of the image.
In this case I made the mask over the trees white so that they will be converted to B&W while leaving the rest of the image in color. Here’s what the mask gives us. Note that the sky, where I went outside the lines is B&W but my intent was to only convert the green in the trees.

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The above examples were just that – examples – and not what anyone would want to live with. Let’s see what’s involved in turning this image into a B&W while retaining the green coloring of the pine trees.
The obvious technique, this is where masks come in, is to mask out the green. NX2 makes this simple – create a mask that’s restricted to green only by simply pointing at the green area with the mouse and clicking (this is what is meant by U Point). Here is the resulting mask (recall that we want to keep the green colors and that the black portion of the mask prevents any adjustment – in this case B&W conversion – from having any effect).

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Not too bad, but notice that there are light areas that need to be darker and vice versa. For example, I’d like to see the trees’ reflections show up as green but in the mask they are nearly white and would be mostly converted to B&W. Solution – point & click again but this time at the reflections which gives us this (mostly) improved mask –

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Oops!! While that made the tree reflection portion of the mask darker, as I wanted, there was some spill over to other parts of the image. Never fear – U Point allows me to mask and to “unmask” and I can solve the problem with a few unmask clicks in the pond area until it is mostly white as seen in the next mask image

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If you enlarge the above mask, you’ll see six control points

  • One in the trees that gave us the original mask in this series
  • One in the tree reflections for the 2nd mask
  • Four in the pond from the step above.

So how long did it take to get to this point – less than 10 seconds, the amount of time that it took to move the mouse and click on each spot to create a control point.
For a final mask refinement, lets clean up the upper half of the image in the same way that the pond was handled. When we do that we get –

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If I wanted to, at this point I could use a brush to further lighten (make white) some of the light gray areas still in the mask – but I won’t bother as they’ll have almost no effect on the  image shown here –

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I mentioned in an earlier post on post-processing, that you really, really want your image editing to be done in a non-destructive manner. When editing is non-destructive the original image is never altered. This means that you can return to the image later and undo/change/add adjustments as you like. As an example, after I completed the above image I decided to add the cattail to the the colored portion of the image. It was easy to do as all I had to do was go back to the mask and add the cattail by clicking on it. While I was at it, I cranked up the saturation a bit and increased the image’s tonal contrast to provide more detail. That gave me this final image –

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For the 3rd installment of this masking series go here.
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