Finding whether a small image is in a big image

[superhero_iceman]

I have the following code, my img1 is big image, and img2 is small image

I think the error is from

If img1.GetPixel(BigX, BigY) <> img2.GetPixel(SmallX, SmallY) Then

    Public Function ImageCompare(ByVal img1 As Bitmap, ByVal img2 As Bitmap)
        Dim coordinates() As Integer = {-1, -1}
        For BigX = 1 To img1.Size.Width - img2.Size.Width + 1
            For BigY = 1 To img1.Size.Height - img2.Size.Height + 1
                For SmallX = 1 To img2.Size.Width
                    For SmallY = 1 To img2.Size.Height
                        If img1.GetPixel(BigX, BigY) <> img2.GetPixel(SmallX, SmallY) Then
                            GoTo Exit_of_this_location
                        End If
                    Next
                Next
                coordinates(0) = BigX + Math.Ceiling(img2.Size.Width / 2)
                coordinates(1) = BigY + Math.Ceiling(img2.Size.Height / 2)
Exit_of_this_location:
            Next
        Next
        Return coordinates
    End Function

Any advice

[jmcilhinney]

I think the error is from

If img1.GetPixel(BigX, BigY) <> img2.GetPixel(SmallX, SmallY) Then

What error? Please provide a FULL and CLEAR explanation of the problem.

[tommytwotrain]

I was trying to answer this all week.

[Shaggy Hiker]

In most cases, that approach will be hopeless. It requires a bunch of things to be true for it to work. For one thing, when you are comparing pixels, you are comparing integers. If you have the RGB color {255, 244,111} and you compare it to a pixel with the color {255,243,111} they won't match, yet the difference is so small that you couldn't see it visually. So, you could have the smaller image shifted by just a single bit from the larger image. You'd see the small in the large, but your code wouldn't find it, because the code would be looking for an exact match.

So, that approach will work if the small really is part of the large, and isn't just "really similar to a part of the large". So, if the small is a set of bytes taken from the bytes of the large, then you will find a match...unless the small image has been transformed in ANY way. If the two are just similar images, such as two different pictures of the same thing, then you'll never get a match with that code.