comparing two images

Posted on 2006-07-17
Last Modified: 2010-04-15
please can anyone provide the code for comparing two images of any type(ppm,pgm,pbm,jpg etc..) and the output will be the number of pixel difference.

Thanks in advance.
Question by:Suhas .
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LVL 11

Assisted Solution

cup earned 50 total points
ID: 17127816
The way I'd approach this is to convert both the images to a common format an then compare them in the common format.

Have a look at the ImageMagick library - they convert everythng to .miff format which might be what you're looking for.  One thing about imagemagick - it relies on dynamic loading of DLLs.  If the DLLs are not there, it doesn't tell you - it just doesn't work.

Big images in high resolutions need tons of memory.  Make sure you have enough.
LVL 53

Expert Comment

ID: 17128111
>> The way I'd approach this is to convert both the images to a common format an then compare them in the common format.
The reason this is a better approach, is because all images are represented differently, and not all of them store the data pixel by pixel. Some are extrapolated, others use vectors. There's also compression to take into account. In the end it's easier to convert to eg. PNG or GIF like cup suggested.

Expert Comment

ID: 17144286

Try to serialize the data as a bit stream.
Then you perform an XOR operation and you got the results. Only different bit pairs are resulted.
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Author Comment

by:Suhas .
ID: 17144342
using fopen we can get the data of two files and comparing byte by byte we get the no. of difference in bytes.

can you please send the code to comare two images of any type?
LVL 53

Expert Comment

ID: 17145454
That's a bit too much work for us to do it for you ... instead read the suggestion made by cup again, and try to work it out yourself. If you have specific questions and or problems about that, feel free to ask them in this thread, and we'll be glad to help you out with them.

Accepted Solution

srinims earned 75 total points
ID: 17152003

    use gdiplus libraries from the microsoft to convert the images of any type to some common types.
   I think gdiplus itself would provide you the comparison methods.
   if do you want the difference in pixel means, i think the output also image.
   you should not use the general bitwise difference. hopefully u may aware of this,

   you have to make difference using RGB values. even RGB1 ~ RGB2 would not provide you the exact diffrences in images, what you have expected.

   for  that you have to convert the RGB format of the image in to HSB i.e Hue, Saturation and Brighness. And then you have to make hsb1~hsb2. then you have to convert the output RGB. That one only will provide you the exact difference in the image itself. Like extracting a image of man(object) from the background, using the two different image with man and without man.

   The things are bit complicated, but you can do

srini ms

Author Comment

by:Suhas .
ID: 17301667
Hi srinims,
can you just give me one example of how to use gdiplus?

also how to convert rgb to hsb and hsb1~hsb2 -> rgb


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