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william_lewis

Beginner

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03-02-2008
05:59 AM

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ippiWarpAffine and ippiGetAffineBound

I am trying to use the function ippiWarpAffine to perform certain transformation of an input image, but am having certain difficulties. Please correct me if i am wrong.

For starters to verify the working of the ippiWarpAffine function, i decided to use it to rotate an image. The affine transfomation matrix for rotation is as follows:

|X| = cos(theta) -sin(theta)

|Y| = sin(theta) cos(theta)

So i define my co-efficients as :

where dAngle is the angle say 10 degress, i.e. 0.1745 in radians

adAffineCoeffs[0][0] = cos(dAngle);

adAffineCoeffs[0][1] = -sin(dAngle);

adAffineCoeffs[0][2] = 0.0;

adAffineCoeffs[1][0] = sin(dAngle);

adAffineCoeffs[1][1] = cos(dAngle);

adAffineCoeffs[1][2] = 0.0;

When i use this in the function ippiGetAffineBound() to get me the bound of the transformed image, of a source image having size:

IppiRect srcRoi;

srcRoi.x = 0;

srcRoi.y = 0;

srcRoi.width =640;

srcRoi.height = 512;

i get the following bound values:

bound[0][0] = -88.732746465172

bound[0][1] = 0.00000000000000

bound[1][0] = 629.29247881179

bound[1][1] = 614.19636580279

Can i know the reason for these negative values. Or is there any mistake in my interpretation. Please help. Thanks in Advance.

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