Image::Leptonica::Func::rotateam
version 0.04
rotateam.c
rotateam.c Grayscale and color rotation for area mapping (== interpolation) Rotation about the image center PIX *pixRotateAM() PIX *pixRotateAMColor() PIX *pixRotateAMGray() Rotation about the UL corner of the image PIX *pixRotateAMCorner() PIX *pixRotateAMColorCorner() PIX *pixRotateAMGrayCorner() Faster color rotation about the image center PIX *pixRotateAMColorFast() Rotations are measured in radians; clockwise is positive. The basic area mapping grayscale rotation works on 8 bpp images. For color, the same method is applied to each color separately. This can be done in two ways: (1) as here, computing each dest rgb pixel from the appropriate four src rgb pixels, or (2) separating the color image into three 8 bpp images, rotate each of these, and then combine the result. Method (1) is about 2.5x faster. We have also implemented a fast approximation for color area-mapping rotation (pixRotateAMColorFast()), which is about 25% faster than the standard color rotator. If you need the extra speed, use it. Area mapping works as follows. For each dest pixel you find the 4 source pixels that it partially covers. You then compute the dest pixel value as the area-weighted average of those 4 source pixels. We make two simplifying approximations: - For simplicity, compute the areas as if the dest pixel were translated but not rotated. - Compute area overlaps on a discrete sub-pixel grid. Because we are using 8 bpp images with 256 levels, it is convenient to break each pixel into a 16x16 sub-pixel grid, and count the number of overlapped sub-pixels. It is interesting to note that the digital filter that implements the area mapping algorithm for rotation is identical to the digital filter used for linear interpolation when arbitrarily scaling grayscale images. The advantage of area mapping over pixel sampling in grayscale rotation is that the former naturally blurs sharp edges ("anti-aliasing"), so that stair-step artifacts are not introduced. The disadvantage is that it is significantly slower. But it is still pretty fast. With standard 3 GHz hardware, the anti-aliased (area-mapped) color rotation speed is about 15 million pixels/sec. The function pixRotateAMColorFast() is about 10-20% faster than pixRotateAMColor(). The quality is slightly worse, and if you make many successive small rotations, with a total angle of 360 degrees, it has been noted that the center wanders -- it seems to be doing a 1 pixel translation in addition to the rotation.
PIX * pixRotateAM ( PIX *pixs, l_float32 angle, l_int32 incolor )
pixRotateAM() Input: pixs (2, 4, 8 bpp gray or colormapped, or 32 bpp RGB) angle (radians; clockwise is positive) incolor (L_BRING_IN_WHITE, L_BRING_IN_BLACK) Return: pixd, or null on error Notes: (1) Rotates about image center. (2) A positive angle gives a clockwise rotation. (3) Brings in either black or white pixels from the boundary.
PIX * pixRotateAMColor ( PIX *pixs, l_float32 angle, l_uint32 colorval )
pixRotateAMColor() Input: pixs (32 bpp) angle (radians; clockwise is positive) colorval (e.g., 0 to bring in BLACK, 0xffffff00 for WHITE) Return: pixd, or null on error Notes: (1) Rotates about image center. (2) A positive angle gives a clockwise rotation. (3) Specify the color to be brought in from outside the image.
PIX * pixRotateAMColorCorner ( PIX *pixs, l_float32 angle, l_uint32 fillval )
pixRotateAMColorCorner() Input: pixs angle (radians; clockwise is positive) colorval (e.g., 0 to bring in BLACK, 0xffffff00 for WHITE) Return: pixd, or null on error Notes: (1) Rotates the image about the UL corner. (2) A positive angle gives a clockwise rotation. (3) Specify the color to be brought in from outside the image.
PIX * pixRotateAMColorFast ( PIX *pixs, l_float32 angle, l_uint32 colorval )
pixRotateAMColorFast() Input: pixs angle (radians; clockwise is positive) colorval (e.g., 0 to bring in BLACK, 0xffffff00 for WHITE) Return: pixd, or null on error Notes: (1) This rotates a color image about the image center. (2) A positive angle gives a clockwise rotation. (3) It uses area mapping, dividing each pixel into 16 subpixels. (4) It is about 10% to 20% faster than the more accurate linear interpolation function pixRotateAMColor(), which uses 256 subpixels. (5) For some reason it shifts the image center. No attempt is made to rotate the alpha component. *** Warning: implicit assumption about RGB component ordering
PIX * pixRotateAMCorner ( PIX *pixs, l_float32 angle, l_int32 incolor )
pixRotateAMCorner() Input: pixs (1, 2, 4, 8 bpp gray or colormapped, or 32 bpp RGB) angle (radians; clockwise is positive) incolor (L_BRING_IN_WHITE, L_BRING_IN_BLACK) Return: pixd, or null on error Notes: (1) Rotates about the UL corner of the image. (2) A positive angle gives a clockwise rotation. (3) Brings in either black or white pixels from the boundary.
PIX * pixRotateAMGray ( PIX *pixs, l_float32 angle, l_uint8 grayval )
pixRotateAMGray() Input: pixs (8 bpp) angle (radians; clockwise is positive) grayval (0 to bring in BLACK, 255 for WHITE) Return: pixd, or null on error Notes: (1) Rotates about image center. (2) A positive angle gives a clockwise rotation. (3) Specify the grayvalue to be brought in from outside the image.
PIX * pixRotateAMGrayCorner ( PIX *pixs, l_float32 angle, l_uint8 grayval )
pixRotateAMGrayCorner() Input: pixs angle (radians; clockwise is positive) grayval (0 to bring in BLACK, 255 for WHITE) Return: pixd, or null on error Notes: (1) Rotates the image about the UL corner. (2) A positive angle gives a clockwise rotation. (3) Specify the grayvalue to be brought in from outside the image.
Zakariyya Mughal <zmughal@cpan.org>
This software is copyright (c) 2014 by Zakariyya Mughal.
This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.
To install Image::Leptonica, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Image::Leptonica
CPAN shell
perl -MCPAN -e shell install Image::Leptonica
For more information on module installation, please visit the detailed CPAN module installation guide.