Photoshop CS4 Channel Apply Image

Question

     Good evening, everybody. I am a beginner of Photoshop and I am really interested in Photoshop.
     Here is a big challenge I have met in the "Image>Apply Image..."
     As it's shown in the picture, I use the Channel Alpha1 to alter the RGB Compound Channel and the Blending mode is ADD. And I can understand the fundamental of the above operation. Then question occur:
    I don't get a full understanding of the Chek Box "Mask..."  and I don't konw what it is used for. And what about some parameters "Image", "Channel", "Layser" about the "Mask..." Can you explain the secret of it to me? It will be much better if you could give me the fundamental or algorithm of it.
    I will really appreciate your reply.
                                                                                                               -----From a Ps Loyal fans

Answer 1

c.pfaffenbichler wrote:
Do you follow some course?
Because in practice this feature seems to hardly get used by most people.
The Apply Image feature is used in fashion portrait retouching when the frequency separation technique is employed. This technique separates texture and color into two layers, which are edited separately. There are several video tutorials showing how it is done, but none of them gets into the details of the Apply Image settings. They just show you what numbers to stick in a few of the boxes. I, too, would like to know more about what those settings do.
An example of one such tutorial is here: http://fstoppers.com/frequency-separation-with-fashion-photographer-retoucher-elena-jasic