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Leptonica 1.68
C Image Processing Library
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Leptonica 1.68
C Image Processing Library
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Interpolated image rotation. More...
Go to the source code of this file.
Functions | |
| PIX * | pixRotateAM (PIX *pixs, l_float32 angle, l_int32 incolor) |
| PIX * | pixRotateAMColor (PIX *pixs, l_float32 angle, l_uint32 colorval) |
| PIX * | pixRotateAMGray (PIX *pixs, l_float32 angle, l_uint8 grayval) |
| PIX * | pixRotateAMCorner (PIX *pixs, l_float32 angle, l_int32 incolor) |
| PIX * | pixRotateAMColorCorner (PIX *pixs, l_float32 angle, l_uint32 fillval) |
| PIX * | pixRotateAMGrayCorner (PIX *pixs, l_float32 angle, l_uint8 grayval) |
| PIX * | pixRotateAMColorFast (PIX *pixs, l_float32 angle, l_uint32 colorval) |
Variables | |
| static const l_float32 | VERY_SMALL_ANGLE = 0.001 |
Interpolated image rotation.
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.
Definition in file rotateam.c.
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.
Definition at line 110 of file rotateam.c.
References ERROR_PTR, FALSE, L_ABS, L_BRING_IN_WHITE, NULL, pixClone(), pixConvertTo8(), pixDestroy(), pixGetDepth(), pixRemoveColormap(), pixRotateAMColor(), pixRotateAMGray(), PROCNAME, REMOVE_CMAP_BASED_ON_SRC, and VERY_SMALL_ANGLE.
Referenced by main(), and pixRotateBinaryNice().
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.
Definition at line 171 of file rotateam.c.
References ERROR_PTR, L_ABS, NULL, pixClone(), pixCreateTemplate(), pixGetData(), pixGetDepth(), pixGetDimensions(), pixGetWpl(), PROCNAME, rotateAMColorLow(), and VERY_SMALL_ANGLE.
Referenced by main(), pixRotate(), and pixRotateAM().
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.
Definition at line 216 of file rotateam.c.
References ERROR_PTR, L_ABS, NULL, pixClone(), pixCreateTemplate(), pixGetData(), pixGetDepth(), pixGetDimensions(), pixGetWpl(), PROCNAME, rotateAMGrayLow(), and VERY_SMALL_ANGLE.
Referenced by main(), pixRotate(), and pixRotateAM().
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.
Definition at line 264 of file rotateam.c.
References ERROR_PTR, FALSE, L_ABS, L_BRING_IN_WHITE, NULL, pixClone(), pixConvertTo8(), pixDestroy(), pixGetDepth(), pixRemoveColormap(), pixRotateAMColorCorner(), pixRotateAMGrayCorner(), PROCNAME, REMOVE_CMAP_BASED_ON_SRC, and VERY_SMALL_ANGLE.
Referenced by main(), and RotateTest().
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.
Definition at line 323 of file rotateam.c.
References ERROR_PTR, L_ABS, NULL, pixClone(), pixCreateTemplate(), pixGetData(), pixGetDepth(), pixGetDimensions(), pixGetWpl(), PROCNAME, rotateAMColorCornerLow(), and VERY_SMALL_ANGLE.
Referenced by pixRotateAMCorner().
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.
Definition at line 368 of file rotateam.c.
References ERROR_PTR, L_ABS, NULL, pixClone(), pixCreateTemplate(), pixGetData(), pixGetDepth(), pixGetDimensions(), pixGetWpl(), PROCNAME, rotateAMGrayCornerLow(), and VERY_SMALL_ANGLE.
Referenced by pixRotateAMCorner().
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.
*** Warning: implicit assumption about RGB component ordering ***
Definition at line 422 of file rotateam.c.
References ERROR_PTR, L_ABS, NULL, pixClone(), pixCreateTemplate(), pixGetData(), pixGetDepth(), pixGetDimensions(), pixGetWpl(), PROCNAME, rotateAMColorFastLow(), and VERY_SMALL_ANGLE.
Referenced by main(), and RotateTest().
const l_float32 VERY_SMALL_ANGLE = 0.001 [static] |
Definition at line 90 of file rotateam.c.
Referenced by pixRotateAM(), pixRotateAMColor(), pixRotateAMColorCorner(), pixRotateAMColorFast(), pixRotateAMCorner(), pixRotateAMGray(), and pixRotateAMGrayCorner().
1.7.3 
