Comparing two images visually

Question

I am wanting to be able to check to see if two images appear to be the same, within a certain threshold.

These two images are the same to the eye, but one has slightly different colors. I have tried the following example:

http://www.vb-helper.com/howto_net_image_compare_threshold.html

Unfortunately, it only seems to detect when the images are identical. How can I determine if the images are the same within a certain threshold, with VB.NET?

Couldn't you just display the image, recapture it and then use the code you have? — stimms
– stimms, Commented Dec 5, 2011 at 4:35
Have you used TinEye.com? They also have an API: ideeinc.com/products/pixmatch - I'm didn't see info on its tolerence but I'm sure there would be many other 3rd party tools that are similar, HTH — Jeremy Thompson
– Jeremy Thompson, Commented Dec 5, 2011 at 5:54

xpda · Accepted Answer · 2011-12-05 06:16:09Z

Resize both images to the same, small size, such as 16x12 or 90x60 (depending on your threshold).
Reduce the color depth to 4 or 8 bits per pixel (not palettized). You might use a posterize function for this.

Then then see if the two smaller images are duplicates. If so, the originals must be pretty close.

endolith · Accepted Answer · 2011-12-05 14:48:09Z

Divide image into R, G, B
For each color:
- For each (x, y):
  - Multiply the pixel of Image 1 with the pixel of Image 2
- Sum all the pixel values
Sum the 3 values for each color

This is the correlation between the two images. To get a value from 0 to 1, first calculate the correlation of an image with itself to see what the best possible value is, then do the correlation of Image 1 with Image 2 and divide by the best possible value.

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