Thank you Jeff.
In fact, my code works fine (!), but because I do not hide the original image / revert the display, I could not saw it. Read below.
Here is the used code:
For loop_Vert = 0 to y
For loop_Hor = 0 to x
Pix_Col = Outline_RGBSurf.Pixel(loop_Hor,loop_Vert)
If Pix_Col = RGB(255,255,255) Then // or If Pix_Col <> RGB(255,255,255) Then … *
Temp_Pict.RGBSurface.Pixel(loop_Hor,loop_Vert) = RGB(0,0,0)
// // Report the actual x,y and pixel colors in a Listbox (LB)
// The_Color = Pix_Col // The_Color is a Variant
// LB.AddRow Str(loop_Hor) + "," + Str(loop_Vert), The_Color
cGraphics.Backdrop = Temp_Pict
* = / <> makes two different images: the mask to the logo as black, the whole image as black excepted the logo as white !
My error: I inverted the layers (Graphics / Backdrop) and not set it back, thus a wrong display. In Window1.MouseDown, I set the original image displayed in .Graphics to Nil to be able to see what I draw in the two loops above.
That is part 1 of what I want to do: I want to draw an outline (black dots around what is not white in the loaded image).
I had the code (working) in my mind since a week or so and today seems to be the good day to check it :(
Now, I have to think to “how to make the artwork outline”.