Adding a Rainbow in Photoshop
If you have a landscape photo that you want to glam-up, you can add a rainbow using Photoshop. You can apply this Photoshop rainbow to any sky, but remember than rainbows usually appear right after a storm.
Step 1: Finding a Rainbow Effect
Immediately create a new layer over the background by going to "Layer", "New", and "Layer". For the sake of organization,
Step 2: Drawing the Rainbow
Click on the icon for "Radial Gradient" in the options bar. You are going to draw a line on your image, which will be interpreted as a line of symmetry by Photoshop. You can draw it either vertically or horizontally as you wish, but either side of the line will be identical to the other. Try it a few times to find the shape that you want.
Step 3: A Step towards Realism
In the layer window, set the "Rainbow" layer's blend mode to "Screen". Now, go to the "Filter" drop-down and select "Blur", then "Gaussian Blur". Adjust the settings as you like, but the idea here is to make the colors blend into each other more naturally. Now you want to fade the rainbow from the land to the sky. Go back to the "Gradient Picker" and pick the "Black, White" gradient. Click on the "Linear Gradient" icon this time. Apply a layer mask to your "Rainbow" layer by clicking on the icon in the layer window that looks like a gray box with a white circle in it.
With the mask selected, you are going to click on your image where the land ends and the sky begins, then pull upward. Stop when you feel that the center of your line is at the same level where you want your rainbow to emerge. Now, it should appear that the rainbow is growing in intensity the higher it rises into the sky. For a little extra punch, duplicate the rainbow layer by going to "Layer", "Duplicate Layer". This should retrieve some of the lost intensity.
Step 4: Fixing Things Up
There is probably some left over rainbow near the bottom of your picture. Select both "Rainbow" layers and group them by going to "Layer", "New", "Group from layers". In the layer window, put a mask on the group as you did earlier. With the mask selected, grab your paint brush tool and paint black over the areas where any unwanted rainbow is lingering.
Now you should have a beautiful rainbow. The steps can be a bit tricky, but this is one of the more convincing effects that is available.
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