CODEWITHSUNDEEP
calgorithmimage-processingeffects
confucius
confucius

Reputation: 13327

Add convex effect to image programmatically

I am looking for some algorithms to add a convex mirror effect and concave mirror effect to an image. I want to know also how to make this efficiently: applying the algorithm to image data or overlay it by a transparent image that contains the effect. But I don't think the second choice is applicable in this case.

Upvotes: 1

Views: 977

Answers (3)

Gil
Gil

Reputation: 3334

If you are doing it manually instead of using hardware primitives, then the bresenham interpolation algorithm (usually used for line drawing) is the way to go: error propagation is far more efficient than other, more complex, methods.

What Bresenham does is just interpolation. Don't miss the opportunity to use its efficient design elsewhere (slope calculation for line-drwaing is just one of the many applications of interpolation: you can interpolate another dimension: 2D, 3D, transparency, reflection, colors, etc.).

25 years ago, I remember having used it to resize bitmaps and even do texture mapping in a real-time 3D engine! That was at a time graphic-accelerated video boards costed a fortune...

Upvotes: 2

Gil
Gil

Reputation: 3334

You can use a pre-calculated sin() table and interpolate values to match the size of your bitmap. The inverse effect is achieved by either using an offset or a larger table.

Remembers me the (great times of the) DOS demos in the 80s...

Upvotes: 1

CapelliC
CapelliC

Reputation: 60024

CImg library has a fisheye sample, in examples\CImg_demo.cpp. The core algorithm seems very simple (and fast, as generally this library). I think it's an approximation of the real optical effect, but could be modified to handle the convex mirroring. I don't know if it could be extended to handle 'negative' curvature.

Upvotes: 2

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