Image scaling and rotating in C/C++

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There are many ways to scale and rotate images. The simplest way to scale is:

dest[dx,dy] = src[dx*src_width/dest_width,dy*src_height/dest_height]

but this produces blocky effects when increasing the size and loss of detail when reducing the size. There are ways to produce better looking results, for example, bilinear filtering.

For rotating, the src pixel location can be calculated using a rotation matrix:

sx,sy = M(dx,dy)

where M is a matrix that maps destination pixels to the source image. Again, you’ll need to do interpolation to produce non-blocky results.

But there are plenty of libraries available if you don’t want to get into the mathematics of image processing.

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