'*************************sobel() subroutine*************************
'
'   purpose: take an image and weight the pixels to find the differences
'            and then save the differences (edges) only
'
'   input: black and white video data in the BWArray array
'          xmask and ymask arrays holding the weights to be given to adjacent pixels
'
'   output: sobel data that is stored in the SobelData array  which is
'           then used in the translate subroutine
'
'********************************************************************
Sub sobel()
    Dim x1 As Integer 'row of picture
    Dim y1 As Integer 'col of picture
    
    Dim sumx As Integer 'sum based on xmask weights
    Dim sumy As Integer 'sum based on ymask weights
    Dim sum As Integer  'overall absolute value of combined weights-->is the final sobel data
    
    Dim i As Integer
    Dim j As Integer
    
    For x1 = 0 To picHEIGHT - 1 'fill in rows 120 to 1
        For y1 = 0 To picWIDTH - 1
             sumx = 0 'reinitialize these to zero every time through the loop
             sumy = 0
             SobelData(y1, x1) = 255 ' initialize each element of the array (avoids separate initializing loop)
             
             'if not on the border of the image, step into the if statement
             If Not (y1 = 0) And Not (y1 = picWIDTH - 1) And Not (x1 = 0) And Not (x1 = picHEIGHT - 1) Then
                 For i = -1 To 1    'work through the masks
                     For j = -1 To 1 'move across columns first, then go to next row
                         'pic is stored (col, row) while the mask is (row,col)
                         'x and i refer to rows, y and j refer to columns
                         sumx = sumx + BWArray((y1 + j), (x1 + i)) * xmask(i + 2, j + 2)
                         sumy = sumy + BWArray((y1 + j), (x1 + i)) * ymask(i + 2, j + 2)
                     Next j
                 Next i
                 
                 sum = Abs(sumx) + Abs(sumy) 'the larger the overall absolute value, the greater the difference
                                             'between the adjacent pixels
                     
                 'adjust the meaning of "black" and "white" via the slider control on the form
                 If sum >= (255 - sliderval) Then
                     sum = 255
                 ElseIf sum <= sliderval Then
                     sum = 0
                 Else
                     sum = 0
                 End If
        
                 SobelData(y1, x1) = 255 - sum 'subtract so edges are outlined in black, everything else is white
             End If
        Next y1
    Next x1
    
    Call translate
    
End Sub