efficient way to compare 2 images?

[bplus]

bplus's demo, modified to just check alpha levels and not colors themselves:

Code: (Select All)

Screen _NewImage(800, 600, 32)
Dim i As Long
For i = 0 To 255
    Cls
    Line (100, 100)-Step(100, 100), _RGB32(255, 0, 0, i), BF
    Line (300, 100)-Step(100, 100), _RGB32(255, 0, 0), BF
    If _Alpha32(Point(150, 150)) = _Alpha32(Point(350, 150)) Then
        Print "When alpha ="; i; " have NO difference, zzz ..."
    Else
        Print "When alpha ="; i; " have difference, zzz ..."
    End If
    Print Hex$(Point(150, 150)), Hex$(Point(350, 150))
    Sleep
Next

Modified to print the actual color values that are on the screen for you.

OK it is a bit of a shocker to see alpha levels stay the same.

But as you can see the red levels are changing with the blend and the whole point my part in this thread was to detect point differences in color which we have until alpha = 255 same as a solid color.

So my question to @SMcneill is are you saying POINT() can't be used to detect differences between 2 images?