Pacific Northwest Nature Photographers Tips, Tricks, Techniques & Tutorials
Creating Selections Via a R/G/B Channel
by Phil Kuglin
by Phil Kuglin
Here is a tutorial on how to quickly create a selection by using a Red/Green or Blue channel and use it for a mask layer on an adjustment layer. This procedure really works well when the area you want to mask has a lot of contrast. For the tutorial I will be using the “Mount Hood w/ beargrass” image I posted. The procedure was done to boost the hue, contrast and brightness of the beargrass.
First here is the image before the procedure:
And after the procedure:
The Procedure
1. The frst step in the procedure is is to decide whioch channel to use: either the red, green or blue channel. In the channel palette click the mouse on each channel's name (reg/green/blue).
For this image I decided to use the red channel. I selected the red channel with the mouse and dragged it to the second icon from the right on the bottom of the channel palette to dupicate the red channel.
2. I then modified this new red channel copy by preforming a level adjustment on it. Make use you use the menu item image/adjustments/levels and not a levels layer. I adjustment the shadow, mid tone and highlight sliders to darken most of the image as I could and boost the contrast of the beargrass:
I zoomed in (ctl/alt/space bar [PC] or command/option/space bar [MAC]) to see how the edges of the beargrass where being defined. Do not worry about completely darkening everything, just define the beargrass since you can modify the channel later:
3. Next, I cleaned up the red channel copy by using either the lasso selection tool and the fill with black command or with a hard brush painting in black. When you are using the brush set the hardness, opacity and fill to 100% with the foreground color set to black. Also you can quickly change the size of the brush via the "[" and "]" keys. The "[" will decrease the brush by 10 pixels (when the size is 10-100) or by 1 (when under 10) and by 25 (when in between 100-200) and even larger beyond 200. The "]" increases the size in the same way. At this point you could run the Gaussian Blur filter (filter/blur/gaussian blur) with a 1-2 pixel value to blur the edges of the channel. This makes the selection blend better, but depends on the selection. I didn't do it for this selection.
You should now have a channel which you can make a selection from.
4. Now create a selection by ctl[PC]/command[MAC] mouse clicking on the red channel copy. You will now see the marching ants around the beargreass. Go back and select the background layer in the layers palette.
5. For the beargrass I wanted to boost the brightness, contrast and adjust the hue. What you may want to do to your selection may be different so you decide. I will explain what I did.
To adjust the hue and brightness I created a hue adjustment layer (layer/new adjustment layer/hue-saturation). If you do this with a selection Photoshop will use the selection for a layer mask. Now I adjusted the hue and brightness of the beargrass. The layer mask only allowed the beargrass to be affected.
6. Finally, I needed to boost the contrast even more through a curve layer. I added a curve layer (layer/new adjustment layer/curves). Then in the curve adjustment layer datalog box I selected the "Use previous layer create a clipping mask". What this does is use the same layer mask as the hue/saturation layer (the layer right below it) did as the base mask. It also adds a blank mask to the curve layer so you can add some unique changes to just the curve adjustment layer, but the base mask starts from the hue/saturation layer. For this layer I didn't modify the mask any. Pretty cool isn't it!
Now, I adjusted the RGB curve and only the beargrass was effected.
And that is all that is to it. Go ahead and give it a shot.