Using Channels
to Select A Dull Sky
And Replace It
With A Dramatic Sky

(Video Of This Technique At The Bottom Of The Page)

Using Channels in Photoshop is a very efficient way to select a complex area of a photograph ...

Original Photograph

like trees against a sky, for instance.

Selecting out all of the little sky bits with any other method (the lasso tool for instance) would make anyone go crazy even if they are using a Wacom tablet. There are just too many little bits to select!

With Channels the job becomes much easier, indeed.

Once your sky is selected out you can replace it with a more dramatic sky.

You can see in this original picture that the sky is a nice blue but it lacks a certain character. Some nice fluffy clouds would certainly make the overall scene just a bit nicer.

How To Replace The Sky

1. You will need a nice dramatic sky picture for this technique. You may find one on-line but you can easily make your own. Get into the habit of shooting fluffy white clouds against a deep blue sky whenever the opportunity presents itself.

2. Before you begin confirm that your sky and foreground picture are the same size! If the foreground picture (that is the one with the boring sky) is 3224 pixels by 2468 pixels and your sky is 1000 pixels by 768 pixels ,,, well they just won''t fit together! Resize the larger one down to the smaller one using Image > Image Size and make sure that Bicubic Sharper at the bottom of the Image Size dialog is chosen before you start resizing.

3. Now that you have two files that are the same size (one foreground and one good sky shot) it is time to begin. The first step is to select the sky out of the foreground file.

   Select Windows > Channels. You will see four channels

   Blue Channel

   named RGB, Red, Blue and Green. When you select either of the Red, Green or Blue Channels you will see the original picture turn to Black and White.

   Inspect each one of them in turn to determine which one has the most contrast between the Sky and the its surroundings (usually the Blue Channel).

   When you have chosen the most contrasty channel, drag it to the New Channel Icon at the bottom of the palette to create a copy.

   Duplicated Blue

   It will be named Blue Copy if you chose Blue.

   
   
   
   

   Black Eyedropper	White Eyedropper

4. Now we are going to Adjust the channel. Select the copy you just created and then choose Image > Adjustments > Levels.

   Near the bottom of the Levels Palette there are three Eyedroppers. The left one is the Black Eyedropper and the right one is the White Eyedropper. Select the Black Eyedropper and click on the darkest part of the image you want to keep.

   The foreground may become totally black but more normally it will have some jet black areas and some areas that are grey. Keep clicking on the grey areas until you get the foreground as dark as possible.

   Now select the White Eyedropper and click on the sky. This turns the sky white (or somewhat whiter). Keep clicking on the sky until it is as white as possible.

   When the channel is as close to black and white as you can get it, click OK.

5. The next step is clean. When you inspect your work to this point you will likely find some white specks in the Black and some black or grey specks in the White part your work.

   The first thing to do is press the D key to get the default colors (Black and White). Make Black the foreground color (press the X key) to bring Black to the top. Select the Brush tool and set the brush to change size with pressure and then start painting away any white in the part of the channel that should be completely Black.

   
   
   Now press the X key again to make White the foreground color and paint any black or grey areas in the sky. When you are finished you should have an image with only two colors - Black and White.

   Just like this ...
   
   

   
   
   Incidentally - those two little black specks in the top left corner are not something that I missed. They are Seagulls!

   Why not take a quick break and get yourself a cooling (or warming) beverage ... ?

   Back? Let's finish this ...

6. Now we want to do something with that nice black and white channel. What we are going to do is load the Channel as a selection.

   To do this hold CTRL (Windows) or CMD (MAC) and click on the name of the channel you are working with (in this case - Blue Copy.

   Now click on the top channel (RGB) to return to the full color image.

   Just to insure that the image is not too crisp click on Select > Feather and set your radius to about 0.5. You can experiment with this setting. Click OK.

7. Switch to the replacement sky, choose Select > All and then Edit > Copy.

   Switch over to the original image on the Layers Palette and choose Edit > Paste Into.

   This will place the new sky on a separate layer with a layer mask. The new layer and the background layer are not linked so you can move the sky around to produce the effect you want with the Move Tool.

8. Now we are at the finishing touches.

   If there is too big a difference between the sky and the foreground simply lower the opacity of the sky layer until you are happy with it.

   When I inspected the tree line in my picture there was some funny fringing between the trees and the sky. If you have the same problem the with the transition this is how to fix it.

   Select Image > Adjustments > Levles and move the sliders around to decrease the fringing. In my case I had to move the middle slider all the way to the left to eliminate the poor transition.

Glow in The Trees	Glow Eliminated

After working through all of these steps, here is what my finished product looks like.