Question

I need a very fast method to detect if an image is empty. Im my case then all pixels are white and transparant.
The images are png’s. My current method is to load them in a memory bitmap and check each pixel value, but this is way to slow.
Is there a more efficient way?

This is my current code:

'Lock the bitmap bits.  
    Dim bmpData As System.Drawing.Imaging.BitmapData = bmp.LockBits(rectBmp, _
        Drawing.Imaging.ImageLockMode.ReadOnly, bmp.PixelFormat)

    Try
        Dim x As Integer
        Dim y As Integer

        For y = 0 To bmpData.Height - 1
            For x = 0 To bmpData.Width - 1
                If System.Runtime.InteropServices.Marshal.ReadByte(bmpData.Scan0, (bmpData.Stride * y) + (4 * x) + 3) <> 0 Then
                    Return True
                    Exit For
                End If
            Next
        Next
    Finally
        bmp.UnlockBits(bmpData)
    End Try

Answer 1

Sure, divide the image by a set amount, for each set start a new thread to only check for non blank pixels (eg not white/transparent).

Create an event that fires (and sets a flag) only if a non empty pixel is found. Have each thread to check this flag (basically a while loop).