[RESOLVED] [2005] Load & Comparing Graphic Files

[John_SC]

Two questions:

1) How do you load a graphic file into a variable in VB? I assumed you would use an Image variable, by how do you load it? I want to load jpg files.

2) How do you compare two graphic files? If I can load the files into Image variables I can use either .equals or .gethashcode methods (and then compare the hashcodes). Is this the best way or is there another?

[jmcilhinney]

1. Image.FromFile

2. Comparing Image objects and comparing images are completely different. The Image.Equals method simply tells you whether two variables refer to the same Image object. If you've called Image.FromFile twice then Equals must return False, even if you called FromFile twice on the same file. If you want to compare image files then you will have to do so by comparing each pixel of the two images. Of course, that's assuming that they're both the same dimensions, which they must be to be the same.

[John_SC]

Image.fromfile seems to work (atleast no errors). I tried comparing hashcodes, and that also does not work, even loading the same file (as you indicated for .equals). So much for the easy way of doing it.

Can you give me any pointers as to how to do the pixel by pixel comparison? I could not find where to get the pixel data. BTW, does this approach work for both jpg and bmp file formats?

[John_SC]

I figured it out. The loaded images had to be loaded as Bitmaps.

Dim img, imgFile As Bitmap
 
 img = Image.FromFile(strTemp.Trim & ".jpg", True)

Then I wrote a function that compared the two images.

Function CompareImages(ByVal imgA As Bitmap, ByVal imgB As Bitmap) As Boolean
        Dim WidthA, WidthB, HeightA, HeightB As Integer
        Dim i, j As Integer
        Dim flag As Boolean
 
        widthA = imgA.Width
        widthB = imgB.Width
        heightA = imgA.Height
        HeightB = imgB.Height
 
        flag = True
        If WidthA = WidthB AndAlso HeightA = HeightB Then
            For i = 0 To WidthA - 1
                For j = 0 To HeightB - 1
                    If imgA.GetPixel(i, j) <> imgB.GetPixel(i, j) Then
                        flag = False
                        i = WidthA
                        j = HeightA
                    End If
                Next
            Next
        Else
            flag = False
        End If
 
        CompareImages = flag
    End Function