ImageChecksum - check if two images are similar

[codeprof]

Tiny procedure to check if two images are similar.
It returns a 192 Bit checksum which can be compared to other checksums.
In contrast to a "normal" checksum(hash) this procedure will return a similar checksum if the two images are similar.
The two images can have different sizes,quality, brightness, contrast, saturation, tinit, noise and will be still considered as the same or similar (only a few bits change).
Not supported at the moment is rotation and horz./vert. flip.

Code: Select all

;AUTHOR:  codeprof
;LICENSE: PUBLIC DOMAIN (can be used without any restriction)

Procedure.s ImageChecksum(image)
  Protected Dim v.i(7,7,1,1)
  Protected img, x, y, c, checksum.s = ""
  img = CopyImage(image,#PB_Any)
  If IsImage(img)
    ResizeImage(img, 64, 64, #PB_Image_Smooth)
    
    StartDrawing(ImageOutput(img))
    For x = 0 To 63
      For y = 0 To 63
        c = Point(x,y)
        v(x >> 3,y >> 3, (x >> 2) & 1 , (y >> 2) & 1 ) + (Red(c) * 3) + (Green(c) * 6) + Blue(c)
      Next
    Next
    StopDrawing()
    For x=0 To 7
      For y=0 To 7
        ;+-
        ;+-            
        If (v(x,y,0,0) + v(x,y,0,1)) - (v(x,y,1,0) + v(x,y,1,1)) > 0
          checksum + "1"
        Else
          checksum + "0"
        EndIf    
        ;++
        ;--
        If (v(x,y,0,0) + v(x,y,1,0)) - (v(x,y,0,1) + v(x,y,1,1)) >= 0
          checksum + "1"
        Else
          checksum + "0"
        EndIf        
        ;+-
        ;-+
        If (v(x,y,0,0) + v(x,y,1,1)) - (v(x,y,0,1) + v(x,y,1,0)) >= 0
          checksum + "1"
        Else
          checksum + "0"
        EndIf    
      Next
    Next
    FreeImage(img)
  EndIf    
  ProcedureReturn checksum
EndProcedure  

Procedure ImageChecksumError(checksum1.s, checksum2.s)
  Protected error = 0
  For i = 1 To 192
    If Mid(checksum1, i, 1) <> Mid(checksum2, i, 1):error+1:EndIf
  Next  
  ProcedureReturn error
EndProcedure




;Example:

UseJPEGImageDecoder()


LoadImage(1,"J:\image1.jpg")
LoadImage(2,"J:\image2.jpg")

Debug ImageChecksum(1)
Debug ImageChecksum(2)

If ImageChecksumError(ImageChecksum(1),ImageChecksum(2)) <= 8
  Debug "Pictures are similar"
Else
  Debug "Pictures are not similar"
EndIf