Create a mask from jpg file and choose the channel to be the opacity with skiasharp

[oscar-bertran]

First at one, I'm sorry for my very bad english.
I'm very new user of skiasharp and i'm thinking how use this tool to obtain some things that I'm thinking. It could be only mind exercices.
I really like the possibilities offered by the color matrix and I use it a lot.
I'm thinking about a function to create a useful mask from jpg file (opaque)
As a enter variables we can have a Skbitmap from the jpg file, the destination size , the channel chossed to be alfa (0 to 3) and a boolean vaulue to invert.
The steps for the function are:

1. Resize the original Skbitmap to the destSksize
2. Create a colormatrix (cm) with 0 values, except the cm(15 + chan) than will be 1 (if invert is false) or -1 (if invert is true, also cm(19)=255)
3. Draw the Skbitmap created at step 1, with the cm at a new Skbitmap
4. The last skbitmap is returned by the function.
   I don't know if this idea are in other discussion, if it this thecase I so sorry for the time lose.
   In all cases thank you very mutch for your attention