How to compare between two images using VB.net? - vb.net

Question

I have a small bitmap image and I will do a screenshot. I need to find whether the small image is the screenshot. How I can compare two bitmap images? and then return the coordinates.
If it is MATLAB, (NOTE: I need VB.net)
What my plan is this
screenshot
for x_screen = 1: screen_width_x
for y_screen = 1: screen_col_y
for x_pic = = 1: pic_width_x
for y_pic = = 1: pic_col_y
if screenshot(x_screen, y_screen) != pic(x_pic , y_pic)
break
end
end
xx = (x_screen)
yy = (y_screen)
end
end

Answer 1

See Image comparison if you want something advanced Also you can look for machine learning techniques for such tasks.
Here is naive solution and not optimized one (plus it is better to do such tasks in native code):
Plus Note that it is better to check this with bmp files. otherwise it will not handle problem
Private Function FindSubImg2(img As Bitmap, subimg As Bitmap) As Point
If (img.Width - subimg.Width < 0) Or (img.Height - subimg.Height < 0) Then Return Nothing
Dim stepxLen As Integer = img.Width - subimg.Width
Dim stepyLen As Integer = img.Height - subimg.Height
Dim coor As Point
Dim match As Boolean = False
For oy As Integer = 0 To stepyLen
For ox As Integer = 0 To stepxLen
match = True
For x As Integer = 0 To subimg.Width - 1
For y As Integer = 0 To subimg.Height - 1
'actually here we do not need ToArgb method. But it will skip unneeded Color comparisions
If img.GetPixel(x + ox, y + oy).ToArgb <> subimg.GetPixel(x, y).ToArgb Then
match = False
Exit For 'we can use goto operator instead of double exit for
End If
Next
If match = False Then Exit For
Next
If match = True Then
coor.X = ox
coor.Y = oy
Return coor
End If
Next
Next
Return New Point(-1, -1)
End Function
Private Function FindSubImg(a As Bitmap, b As Bitmap) As Point
Dim subimg As Bitmap
Dim img As Bitmap
If (a.Height <= b.Height AndAlso a.Width <= b.Width) Then
subimg = a : img = b
Return FindSubImg2(img, subimg)
ElseIf (a.Height > b.Height AndAlso a.Width > b.Width) Then
subimg = b : img = a
Return FindSubImg2(img, subimg)
Else
Return New Point(-1, -1)
End If
End Function
Usage:
Dim p As Point = FindSubImg(New Bitmap("A.bmp"), New Bitmap("B.bmp"))

Answer 2

Try something like this:
Public Function CompareImages(ByVal img1 As Bitmap, ByVal img2 As Bitmap) As Boolean
Dim i As Integer
Dim j As Integer
For i = 0 To img1.Width - 1
For j = 0 To img2.Height - 1
If img1.GetPixel(i, j) <> img2.GetPixel(i, j) Then
Return False
End If
Next
Next
Return True
End Function
sample call:
CompareImages(New Bitmap("f:\img1.bmp"), New Bitmap("f:\img2.bmp"))