124 lines
3.5 KiB
Groff
124 lines
3.5 KiB
Groff
.TH CONVOLUTION 3 "2 May 1991"
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.SH NAME
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im_conv, im_convf, im_convsep, im_convsepf,
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im_convsub, im_shrink \- convolves an image with a generalised
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mask
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.SH SYNOPSIS
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#include <vips/vips.h>
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int im_conv(in, out, mask)
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.br
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IMAGE *in, *out;
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.br
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INTMASK *mask;
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int im_convf(in, out, mask)
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.br
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IMAGE *in, *out;
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.br
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DOUBLEMASK *mask;
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int im_convsep(in, out, mask)
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.br
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IMAGE *in, *out;
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.br
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INTMASK *mask;
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int im_convsepf(in, out, mask)
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.br
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IMAGE *in, *out;
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.br
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DOUBLEMASK *mask;
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int im_convsub(in, out, mask, xskip, yskip)
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.br
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IMAGE *in, *out;
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.br
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INTMASK *mask;
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.br
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int xskip, yskip;
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int im_shrink(in, out, xfactor, yfactor)
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.br
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IMAGE *in, *out;
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.br
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double xfactor, yfactor;
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.SH DESCRIPTION
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These functions
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convolve the image pointed by the image descriptor in with the file
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pointed by mask and puts the result in the image pointed by out.
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The mask structures INTMASK and DOUBLEMASK are
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returned by the function im_read_imask(3) or im_read_dmask(3),
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for integer and double masks respectively.
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Input should be non-complex.
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The size and type of the output image are the same as the size of the input.
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To
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output a larger type (for example, to output an int image from convolution
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of a byte image, avoiding clipping), cast the input image up with one of
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the im_clip2*() functions.
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If the sizes of the mask are xm and ym and the sizes of the image are xs and ys,
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then there is a black border at the output image as follows:
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The top ym/2 lines black, bottom ys-ym/2-ym lines black; each of the remaining
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lines has the initial xm/2 pels blank, and the final
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xs-xm/2-xm pels (division over 2 is integer division).
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The output at each point is divided by scale and then the offset is added.
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Both offset and scale are held in mask.
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.B im_conv()
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and
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.B im_convsep()
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have 'raw' versions which do not add the black border: instead the output
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image is smaller than the input.
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.B im_conv()
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and
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.B im_conv_raw()
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convolve any non-complex input image to make an output image of the same
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type. Rounding is appropriate to the image type.
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.B im_convf()
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convolves to float (double if the input is double).
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The function expects a double mask.
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.B im_convsep()
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and
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.B im_convsep_raw()
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carry out convolution using an 1xN or Nx1 separable mask.
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The function
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scales the output result by dividing it with scale*scale. The scale
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factor should therefore be the sqrt of the scale of the square NxN mask.
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Rounding is appropriate to the image type. It works on any non-complex image,
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and writes the output in the same format as the input.
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The function expects integer mask.
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.B im_convsepf()
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convolves to float (double if the input is double).
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The function expects a double mask.
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.B im_convsub()
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convolves the byte image pointed by in and writes the result as a byte output.
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Using this function the input image is subsampled on
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both directions by an integer factor of xskip horizontally and
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an integer factor of yskip vertically.
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During the covolution, values are rounded before division.
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Both input and output are bytes. Output is clipped between 0 and 255.
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The function expects an integer mask.
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.B im_shrink()
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shrink the input image file by xfactor along the horizontal and
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yfactor along the vertical direction. The function doesnot perform subpixel
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interpolation and therefore the resultant image can present aliasing especially
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for small x and y factors. Any size image, any non-complex type, any number of
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bands.
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.SH RETURN VALUE
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The function returns 0 on success and -1 on error.
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.SH SEE ALSO
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im_read_imask(3), im_compass(3), im_fastcor(3).
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