comparing images [ got the code need explination]

hi every one

my question is same as my topic I want to compare two images and deside which one are same .

I got no clue where to start

thx for future help

Code:

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Private Sub btnGo_Click(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles btnGo.Click
    Me.Cursor = Cursors.WaitCursor
    Application.DoEvents()

    ' Get the threshold.
    Dim threshold As Integer = _
        Integer.Parse(txtThreshold.Text)

    ' Load the images.
    Dim bm1 As Bitmap = Image.FromFile(txtFile1.Text)
    Dim bm2 As Bitmap = Image.FromFile(txtFile2.Text)

    ' Make a difference image.
    Dim wid As Integer = Math.Min(bm1.Width, bm2.Width)
    Dim hgt As Integer = Math.Min(bm1.Height, bm2.Height)
    Dim bm3 As New Bitmap(wid, hgt)

    ' Create the difference image.
    Dim are_identical As Boolean = True
    Dim r1, g1, b1, r2, g2, b2, r3, g3, b3 As Integer
    Dim color1, color2 As Color
    Dim eq_color As Color = Color.White
    Dim ne_color As Color = Color.Red
    Dim dr, dg, db, diff As Integer
    For x As Integer = 0 To wid - 1
        For y As Integer = 0 To hgt - 1
            color1 = bm1.GetPixel(x, y)
            color2 = bm2.GetPixel(x, y)
            dr = CInt(color1.R) - color2.R
            dg = CInt(color1.G) - color2.G
            db = CInt(color1.B) - color2.B
            diff = dr * dr + dg * dg + db * db
            If diff <= threshold Then
                bm3.SetPixel(x, y, eq_color)
            Else
                bm3.SetPixel(x, y, ne_color)
                are_identical = False
            End If
        Next y
    Next x

    ' Display the result.
    picResult.Image = bm3

    Me.Cursor = Cursors.Default
    If (bm1.Width <> bm2.Width) OrElse (bm1.Height <> _
        bm2.Height) Then are_identical = False
    If are_identical Then
        MessageBox.Show("The images are identical")
    Else
        MessageBox.Show("The images are different")
    End If

    bm1.Dispose()
    bm2.Dispose()
End Sub

---

http://www.vb-helper.com/howto_net_i...threshold.html

I found this code and I need some explination

thx for the help

It compares the difference of the color of the pixels. If it falls under some threshold, the pixels are considered similar, if it doesn't the pixels are considered not similar. It also outputs an image of the same size that gives you a visual indicator of where the difference lies.

If you are trying to determine if they are identical, you don't need to do this much work. You could check the sizes of the files and also compute an MD5 hash of the file.

I got every thing u said execpt the this part

can u pls expalin this part again

Quote:

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also compute an MD5 hash of the file.

---

thx for ut help

is this like this ??

Code:

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Imports System.Text
Imports System.Security.Cryptography

Private Function GenerateHash(ByVal SourceText As String) As String
'Create an encoding object to ensure the encoding standard for the source text
Dim Ue As New UnicodeEncoding()
'Retrieve a byte array based on the source text
Dim ByteSourceText() As Byte = Ue.GetBytes(SourceTStext)
'Instantiate an MD5 Provider object
Dim Md5 As New MD5CryptoServiceProvider()
'Compute the hash value from the source
Dim ByteHash() As Byte = Md5.ComputeHash(ByteSourceText)
'And convert it to String format for return
Return Convert.ToBase64String(ByteHash)
End Function

---

source :
http://www.a1vbcode.com/vbtip-149.asp


how do i do that with image

You can get the bytes of the image and pass it to the MD5.ComputeHash function.

VB Code:

MessageBox.Show(Convert.ToBase64String(Md5.ComputeHash(New System.IO.StreamReader("C:\Temp\2006_01_07\IMG_2809.JPG").BaseStream)))

Now if the MD5 hashes are identical, it does not guarantee that the files are exactly the same, however, it is a pretty good indicator, especially if the files are the same size.

Is it posible for md5 hash to show same string even thow it not same

Technically, yes. However, very similar files (i.e. off by only a few bytes) will have drastically different MD5 hashes.

The only way to be 100% sure that it is the exact same file, would be comparing every single byte in the files.

Okay Thx I Will Try That Code And Ask If Any Help Is Needed