CODEWITHSUNDEEP
objective-ccocoa-touchopengl-esavfoundationcore-image
anon_dev1234
anon_dev1234

Reputation: 2153

Cropping Using OpenGL ES 2.0 iOS (vs. using Core Image)

I'm having difficulties finding any documentation about cropping images using OpenGL ES on the iPhone or iPad.

Specifically, I am capturing video frames at a mildly rapid pace (20 FPS), and need something quick that will crop an image. Is it feasible to use OpenGL here? If so, will it perform faster than cropping using Core Image and its associated methods?

It seems that using Core Image methods, I can't achieve faster than about 10-12 FPS output, and I'm looking for a way to hit 20. Any suggestions or pointers to usage of OpenGL for this?

Upvotes: 3

Views: 1812

Answers (1)

zhzhy
zhzhy

Reputation: 461

Obviously, using OpenGl ES will be faster than Core Image Framework. Cropping image will be done by set Texture Coordinate, in generally, Texture Coordinate always like this,

{
0.0f,1.0f,
1.0f,1.0f,
0.0f,0.0f,
1.0f.0.0f
}

The whole image will be drawed with Texture Coordinate above. If you just want upper right part of a image, you can set Texture Coordinate like this,

{
0.5f,1.0f,
1.0f,1.0f,
0.5f,0.5f,
1.0f.0.5f
}

This will get a quater of the whole image at upper right. You never forget that the Coordinate origin of OpenGl ES is at the lower left corner

Upvotes: 3

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