Affinity photo blend modes are one of the best shortcuts available when compositing images. If a lighten only or darken only blend mode work for the hard parts of your composite (the edges) then it will greatly simplify compositing.
Fixing a “oops” Using Lighten Only Blending
The rain “failed” during a recent “soaked” portrait shoot with Triphop artist Meganoke. It was only for a few frames, but one of those happen to be my favorite expression. I had lots of frames with rain available. I just had to bring them together. Because I was shooting hard black and white the background is black and the rain drops are bright, using a lighten only blend mode is a great way to composite the rain from another shot into this image.
Affinity Photo Blend Modes
I chose an image with similar proportions and layered it over the target image using the Lighten blend mode. The lighten blend mode only shows pixels that are brighter than layers below it.
As you can see, in the lighten blending (left side), the resulting image is the lightest pixels from the two images. For the darken blending (right side), the resulting image is the darkest pixels from the two images.
Frequently, objects we want to composite in are brighter than the background and lighten blend makes it easy. This is exactly the same mechanism that allows stacked star trails to come together relatively easily.
The Final Product
Combined with a little crude masking, restoring the missing rain to the photo was simple and quick.