what exactly happend when you use the command imresize?

what exactly happend when you use the command imresize? does it means compression? will it affect the image quality?

Answer 1

[Alex Taylor]

This question has essentially been asked before:

http://www.mathworks.com/matlabcentral/answers/82893-how-does-the-function-imresize-work-in-details

In short, resizing is a geometric transformation, or more precisely a scale transformation. For each pixel in the output image, imresize is doing a point transformation to find where the corresponding point maps in the input image. Once imresize has formed a collection of remapped points, interpolatation is performed to resolve sub-pixel remapped locations (the default of imresize is bicubic interpolation).

If the output image is being scaled with a scale factor less than 1, then by default a low-pass anti-aliasing filter is applied to the input image prior to the steps described above to prevent high frequency content from the input image introducing distortions due to downsampling the input image. You can turn this anti-aliasing filtering off to see how it effects results. It's generally a very important step when down sizing an image to get visually nice looking resized images.

Answer 2

[Jan]

The image array is resized as explained in the documentation:

doc imresize

So if you have a 100x100 pixel image, you can transform it into a 200x200 or 20x30 pixel image. Resizing destroys information when you reduce the size and even increasing the size will reduce the quality at least a little bit due to rounding errors.