Thread: how to open two image and substract them?

hi,
does anyone know how to write in C programming to open two images and subtract them to get a result ? please take note that the image is an grayscale image.

thanks.

You need some sort of library that can read the image format you have - it may be part of your OS, or you may need some third party product [free or commercial]. Once you have something that can load the images and take byte by byte and subtract one from the other, and store the result as another image [or whatever you want to do with the result].

Of course, you CAN write your own routines to load an image, but I wouldn't recommend it.

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Mats

Originally Posted by valy_mil

hi,
does anyone know how to write in C programming to open two images and substract them to get a result ? please take note that the image is an grayscale image.

thanks.

We all know a bit about writing in C - check. Images are just files with a particular format so - check.

"Substract" == subtract. Here, I need a much better explanation of what you want. Subtract the area of one from the area of the second one, subtract the light/dark value's from each other, what?

It would be best if you could load an example showing the two input and one output image to Photobucket, and paste the url here so we can see what you mean.

And of course, show us your work on this. We won't write your program for you.

If this isn't a programming assignment, you might want to check with Gimp and other image manipulators. They may well have a facility to automatically do that for you.

Of course, you can use fopen() on an image file - the problem is that even the simplest of image files (such as Windows BMP's) aren't particularly easy to read straight away, and it gets even worse if the image is a TIFF, JPEG, PNG, GIF etc, as those have a more complex structure.

Since there are libraries [e.g. libjpeg] that allow you to build an application that can just load a JPEG image and then access the data directly, why bother with writing hundreds or thousands of lines of code to read the image, only to do a simple operation on the data loaded [if I assume correctly that you just want to subtract each pixel from one image from the corresponding pixel of the other image].

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Mats

So you need to have a library that supports JPEG images and BMP, and then you need some algorithm for converting to grayscale [unless the input JPEG is a grayscale already].

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Mats

Just google for "bmp file format". There's plenty of info out there.