Adding trees to a sunset

6 Oct

The problem:

  • My wife said: “Hopelessly overexposed, but the trees look nice. Perhaps you could replace the sky?”

Steps I took:

  • Here’s a sunset shot from the same evening, with some nice dramatic clouds, but a bit naff at the bottom.

  • Make a copy of the “trees” image and convert it to greyscale.

  • Select the main chunk of sky, staying away from the trees, and change it to white. Red is just to show the selection I used.

  • Use a round brush (in my case 50 pixels) of white to refine the edges around the trees and change it to white.  It’s better to eat a little tree than to leave a splodge in the sky. This is also a good time to clone out any annoyances in the image, in this case a roof and chimney.

  • Adjust the contrast. I used +50%.

A note on alpha masks:

  • If you’re not familiar with alpha masks (masks for short), these are just a 2 dimensional pattern of transparency. They can vary from opaque to transparent and anywhere in between. Each pixel location gets its own level of transparency. Conveniently, you can display, edit, and convert from/to as a greyscale image.

A mask can cover a layer completely or with varying levels of opacity. The grey value of the mask determines how much it covers. Where it is black, it completely masks the layer, producing a transparent area; where it is white, it leaves the layer unmasked (in its original state); where it is grey, it produces a semi-masking effect, with the transparency increasing as the grey becomes darker.   (from the PaintShop Pro help)

My first, failed, attempt:

  • I took my “trees” image and created an alpha mask (in Paintshop Pro that’s [Mask], [New], [from Image] and select the greyscale picture). This leaves just the trees on a transparent background.

  • Then I slid a copy of the “clouds” image BEHIND the masked trees, and moved it down a bit to provide a background. As you can see, it didn’t work, especially in the trees at the right.

  • I tried various techniques of blurring the mask, or having multiple layers with different masks, but nothing worked well.

A better way:

  • I took my “scrolled down clouds” image.

  • And I applied the tree mask to that (inverted, of course). This gave me a cloudscape with holes.

  • And then I just put a background layer of black BELOW the masked clouds.

  • A final crop and the result looks – in my opinion – better than either of the source images.

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