VB.NET Arithmetic operation caused an overflow

Question

I have a function that changes the brightness of an image.

However I am getting the error "Arithmetic operation caused an overflow. You may not divide by 0.". in the line

bData.ByteData(ii) = CByte(bData.ByteData(ii) + (amount * (255 - bData.ByteData(ii)))) 'blue

"amount" is 30.

I am not sure what I did wrong. Does anybody see my error? Thank you!

    Public Sub Brightness(Optional ByVal amount As Single = 0)
        OnFilterStarted()
        If amount = 0 Then Return
        Dim bData = BitmapData.LockBits(b)
        If amount > 0 Then
            For ii = bData.ByteData.GetLowerBound(0) To bData.ByteData.GetUpperBound(0) Step 4
                bData.ByteData(ii) = CByte(bData.ByteData(ii) + (amount * (255 - bData.ByteData(ii)))) 'blue
                bData.ByteData(ii + 1) = CByte(bData.ByteData(ii + 1) + (amount * (255 - bData.ByteData(ii + 1)))) 'green
                bData.ByteData(ii + 2) = CByte(bData.ByteData(ii + 2) + (amount * (255 - bData.ByteData(ii + 2)))) 'red
            Next
        Else
            For ii = bData.ByteData.GetLowerBound(0) To bData.ByteData.GetUpperBound(0) Step 4
                bData.ByteData(ii) = CByte(bData.ByteData(ii) - (Math.Abs(amount) * bData.ByteData(ii))) 'blue
                bData.ByteData(ii + 1) = CByte(bData.ByteData(ii + 1) - (Math.Abs(amount) * bData.ByteData(ii + 1))) 'green
                bData.ByteData(ii + 2) = CByte(bData.ByteData(ii + 2) - (Math.Abs(amount) * bData.ByteData(ii + 2))) 'red
            Next
        End If
        bData.UnlockBits()
        OnFilterFinished()
    End Sub

Show us the value of ByteData(ii) when this happens. I'm pretty sure the result goes beyond the boundary of a byte. If you multiply by 30, you aren't giving yourself a lot of space. You're overflow isn't caused by a divide. — the_lotus
– the_lotus, Commented Apr 10, 2014 at 19:21
@the_lotus Indeed. The only valid value for the input byte that WON'T cause an overflow is 255. — mafafu
– mafafu, Commented Apr 10, 2014 at 19:22

the_lotus · Accepted Answer · 2014-04-10 19:23:52Z

1

Show us the value of ByteData(ii) when this happens. I'm pretty sure the result goes beyond the boundary of a byte. If you multiply by 30, you aren't giving yourself a lot of space. You're overflow isn't caused by a divide.

Example, this will cause the error.

    Dim b As Byte
    Dim a As Single

    b = 128
    a = 30

    b += a * (255 - b)

The only way for it to not cause an error is if b is equal to 255 (thanks mafafu).

answered Apr 10, 2014 at 19:23

the_lotus

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