How does the Apply Image option work in Adobe Photoshop?

Question

Adobe

What is it for? How to use it predictably?
How the options work - Preserve Transparency , Mask I don't understand these two options at 100% at all

Answer 1

This function allows you to transfer color information from one channel of the source image to another channel of the target image. As an option - from channel to channel of the same image (source and target are the same).
Suppose the task is to make a single-channel from four-channel CMYK. You can, of course, stupidly convert to grayscale, but in this case there is less control over the color (greyscale is rendered a little differently), or for example, the tipuha requires that only CMYK images and a dot be in the layout, and we need to link black and white photo.
In turn, apply the image from C, M, Y channels to the K channel, after which we clear the C, M, Y channels. Outwardly, the same grayscale will turn out, but along the way, you can edit the channels and achieve greater image accuracy in the target channel.
The same algorithm is used if you need to prepare a layout for printing in 2-3 colors from a finished design (cheap mass replication). We scatter the information about the color into the target channels, we clean the unnecessary ones.
It also helps when there are more channels than standard ones - for example, you need to convert a CMYK layout to Pantones, and some idiot glued all the layers together))) It doesn’t matter, working with channels comes to the rescue. You create pantone channels and transfer color information from C, M, Y, K channels there, erase the latter and voila - you have a layout from custom channels ...
Well, not to mention transferring one or another color cast from the channel of one image to the channel of another (there can be a lot of applications, I described cases from my experience).