How do I rotate each block of image to be perpendicular to x-axis?

For each block of a fingerprint image, the local orientation is measured. I tried to rotate gradients by their mean orientation but it looks same as gradients and not perpendicular to x-axis.

Answer 1

[Image Analyst]

You could use imrotate() on the block, or use various combinations of transpose (the ' operator), flipud(), and fliplr().

[Klara]

What if I don't have image processing toolbox?

[Image Analyst]

transpose and flip functions are in Base MATLAB so you have them.

[Klara]

Thanks. How to get ensure that after rotation, it's angle to the x-axis is 90 degree?

[Image Analyst]

What's angle? The block will always have sides at 0 and 90 since it's rectangular. And some arbitrary fingerprint ridges inside the block will have gradient vectors at a bunch of arbitrary angles.

[Klara]

Because its asked to Rotate the block such that the dominant ridge flow is perpendicular to the x-axis. Is there any formula to rotate each block in this way?

[Image Analyst]

You didn't say that before. First you need to determine the dominant ridge flow angle somehow (think up some method or follow a paper that describes it), then use imrotate with that angle.

[Klara]

Thanks. Reminding that I don't have Image Processing Toolbox, then is is possible to rotate it based on Rotation matrix?

[Image Analyst]

Yes.