vips_shrink ()

intvips_shrink (VipsImage *in,VipsImage **out,double hshrink,double vshrink,...);

Optional arguments:

Shrinkin by a pair of factors with a simple box filter. For non-integerfactors,vips_shrink() will first shrink by the integer part with a boxfilter, then usevips_reduce() to shrink by theremaining fractional part.

This is a very low-level operation: seevips_resize() for a moreconvenient way to resize images.

This operation does not change xres or yres. The image resolution needs tobe updated by the application.

See also:vips_resize(),vips_reduce().

[method]

vips_shrinkh ()

intvips_shrinkh (VipsImage *in,VipsImage **out,int hshrink,...);

Optional arguments:

Shrinkin horizontally by an integer factor. Each pixel in the output isthe average of the corresponding line ofhshrink pixels in the input.

This is a very low-level operation: seevips_resize() for a moreconvenient way to resize images.

This operation does not change xres or yres. The image resolution needs tobe updated by the application.

See also:vips_shrinkv(),vips_shrink(),vips_resize(),vips_affine().

[method]

vips_shrinkv ()

intvips_shrinkv (VipsImage *in,VipsImage **out,int vshrink,...);

Optional arguments:

Shrinkin vertically by an integer factor. Each pixel in the output isthe average of the corresponding column ofvshrink pixels in the input.

This is a very low-level operation: seevips_resize() for a moreconvenient way to resize images.

This operation does not change xres or yres. The image resolution needs tobe updated by the application.

See also:vips_shrinkh(),vips_shrink(),vips_resize(),vips_affine().

[method]

vips_reduce ()

intvips_reduce (VipsImage *in,VipsImage **out,double hshrink,double vshrink,...);

Optional arguments:

Reducein by a pair of factors with a pair of 1D kernels. Thiswill not work well for shrink factors greater than three.

Setgap to speed up reducing by havingvips_shrink() to shrinkwith a box filter first. The biggergap, the closer the resultto the fair resampling. The smallergap, the faster resizing.The default value is 0.0 (no optimization).

This is a very low-level operation: seevips_resize() for a moreconvenient way to resize images.

This operation does not change xres or yres. The image resolution needs tobe updated by the application.

See also:vips_shrink(),vips_resize(),vips_affine().

[method]

vips_reduceh ()

intvips_reduceh (VipsImage *in,VipsImage **out,double hshrink,...);

Optional arguments:

Reducein horizontally by a float factor. The pixels inout areinterpolated with a 1D mask generated bykernel.

Setgap to speed up reducing by havingvips_shrinkh() to shrinkwith a box filter first. The biggergap, the closer the resultto the fair resampling. The smallergap, the faster resizing.The default value is 0.0 (no optimization).

This is a very low-level operation: seevips_resize() for a moreconvenient way to resize images.

This operation does not change xres or yres. The image resolution needs tobe updated by the application.

See also:vips_shrink(),vips_resize(),vips_affine().

[method]

vips_reducev ()

intvips_reducev (VipsImage *in,VipsImage **out,double vshrink,...);

Optional arguments:

Reducein vertically by a float factor. The pixels inout areinterpolated with a 1D mask generated bykernel.

Setgap to speed up reducing by havingvips_shrinkv() to shrinkwith a box filter first. The biggergap, the closer the resultto the fair resampling. The smallergap, the faster resizing.The default value is 0.0 (no optimization).

This is a very low-level operation: seevips_resize() for a moreconvenient way to resize images.

This operation does not change xres or yres. The image resolution needs tobe updated by the application.

See also:vips_shrink(),vips_resize(),vips_affine().

[method]

vips_thumbnail ()

intvips_thumbnail (constchar *filename,VipsImage **out,int width,...);

Optional arguments:

Make a thumbnail from a file. Shrinking is done in three stages: using anyshrink-on-load features available in the file import library, using a blockshrink, and using a lanczos3 shrink. At least the final 200% is done withlanczos3. The output should be high quality, and the operation should bequick.

Seevips_thumbnail_buffer() to thumbnail from a memory buffer, orvips_thumbnail_source() to thumbnail from an arbitrary byte source.

By default, libvips will only use the first frame of animated or multipageimages. To thumbnail all pages or frames, passn=-1 to the loader infilename, for example"x.gif[n=-1]".

The output image will fit within a square of sizewidth xwidth. You canspecify a separate height with theheight option. Set eitherwidth orheight to a very large number to ignore that dimension.

If you setcrop, then the output image will fill the whole of thewidth xheight rectangle, with any excess cropped away. Seevips_smartcrop() fordetails on the cropping strategy.

Normally the operation will upsize or downsize as required to fit the imageinside or outside the target size. Ifsize is settoVIPS_SIZE_UP, the operation will only upsize and will justcopy if asked to downsize.Ifsize is settoVIPS_SIZE_DOWN, the operation will only downsize and will justcopy if asked to upsize.Ifsize isVIPS_SIZE_FORCE, the image aspect ratio will be broken and theimage will be forced to fit the target.

Normally any orientation tags on the input image (such as EXIF tags) areinterpreted to rotate the image upright. If you setno_rotate toTRUE,these tags will not be interpreted.

Shrinking is normally done in sRGB colourspace. Setlinear to shrink inlinear light colourspace instead. This can give better results, but canalso be far slower, since tricks like JPEG shrink-on-load cannot be used inlinear space.

If you setexport_profile to the filename of an ICC profile, the imagewill be transformed to the target colourspace before writing to theoutput. You can also give animport_profile which will be used if theinput image has no ICC profile, or if the profile embedded in theinput image is broken.

Useintent to set the rendering intent for any ICC transform. The defaultisVIPS_INTENT_RELATIVE.

Usefail_on to control the types of error that will cause loading to fail.The default isVIPS_FAIL_ON_NONE, ie. thumbnail is permissive.

See also:vips_thumbnail_buffer().

vips_thumbnail_buffer ()

intvips_thumbnail_buffer (void *buf,size_t len,VipsImage **out,int width,...);

Optional arguments:

Exactly asvips_thumbnail(), but read from a memory buffer. One extraoptional argument,option_string, lets you pass options to the underlyingloader.

See also:vips_thumbnail().

vips_thumbnail_image ()

intvips_thumbnail_image (VipsImage *in,VipsImage **out,int width,...);

Optional arguments:

Exactly asvips_thumbnail(), but read from an existing image.

This operationis not able to exploit shrink-on-load features of image load libraries, soit can be much slower thanvips_thumbnail() and produce poorer qualityoutput. Only use it if you really have to.

See also:vips_thumbnail().

[method]

vips_thumbnail_source ()

intvips_thumbnail_source (VipsSource *source,VipsImage **out,int width,...);

Optional arguments:

Exactly asvips_thumbnail(), but read from a source. One extraoptional argument,option_string, lets you pass options to the underlyingloader.

See also:vips_thumbnail().

vips_similarity ()

intvips_similarity (VipsImage *in,VipsImage **out,...);

Optional arguments:

This operator callsvips_affine() for you, calculating the matrix for theaffine transform fromscale andangle. Other parameters are passed on tovips_affine() unaltered.

See also:vips_affine(),VipsInterpolate.

[method]

vips_rotate ()

intvips_rotate (VipsImage *in,VipsImage **out,double angle,...);

Optional arguments:

This operator callsvips_affine() for you, calculating the matrix for theaffine transform fromscale andangle. Other parameters are passed on tovips_affine() unaltered.

See also:vips_affine(),VipsInterpolate.

[method]

vips_affine ()

intvips_affine (VipsImage *in,VipsImage **out,double a,double b,double c,double d,...);

Optional arguments:

This operator performs an affine transform on an image usinginterpolate.

The transform is:

1234567

X=@a*(x+@idx)+@b*(y+@idy)+@odxY=@c*(x+@idx)+@d*(y+@idy)+@doywhere:xandyarethecoordinatesininputimage.XandYarethecoordinatesinoutputimage.(0,0)istheupperleftcorner.

The section of the output space defined byoarea is written toout.oarea is a four-element int array of left, top, width, height.By defaultoarea is just large enough to cover the whole of thetransformed input image.

By default, new pixels are filled withbackground. This defaults tozero (black). You can set other extend types withextend.VIPS_EXTEND_COPYis better for image upsizing.

interpolate defaults to bilinear.

idx,idy,odx,ody default to zero.

Image are normally treated as unpremultiplied, so this operation can be useddirectly on PNG images. If your images have been throughvips_premultiply(),setpremultiplied.

This operation does not change xres or yres. The image resolution needs tobe updated by the application.

See also:vips_shrink(),vips_resize(),VipsInterpolate.

[method]

vips_resize ()

intvips_resize (VipsImage *in,VipsImage **out,double scale,...);

Optional arguments:

Resize an image.

Setgap to speed up downsizing by havingvips_shrink() to shrinkwith a box filter first. The biggergap, the closer the resultto the fair resampling. The smallergap, the faster resizing.The default value is 2.0 (very close to fair resamplingwhile still being faster in many cases).

vips_resize() normally usesVIPS_KERNEL_LANCZOS3 for the final reduce, youcan change this withkernel. Downsizing is done with centre convention.

When upsizing (scale > 1), the operation usesvips_affine() withaVipsInterpolate selected depending onkernel. It will useVipsInterpolateBicubic forVIPS_KERNEL_CUBIC and above. It adds a0.5 pixel displacement to the input pixels to get centre convention scaling.

vips_resize() normally maintains the image aspect ratio. If you setvscale, that factor is used for the vertical scale andscale for thehorizontal.

If either axis would drop below 1px in size, the shrink in that dimensionis limited. This breaks the image aspect ratio, but prevents errors due tofractional pixel sizes.

This operation does not change xres or yres. The image resolution needs tobe updated by the application.

This operation does not premultiply alpha. If your image has an alphachannel, you should usevips_premultiply() on it first.

See also:vips_premultiply(),vips_shrink(),vips_reduce().

[method]

vips_mapim ()

intvips_mapim (VipsImage *in,VipsImage **out,VipsImage *index,...);

Optional arguments:

This operator resamplesin usingindex to look up pixels.out isthe same size asindex, with each pixel being fetched from that position inin. That is:

1

out[x,y]=in[index[x,y]]

Ifindex has one band, that band must be complex. Otherwise,index musthave two bands of any format.

Coordinates inindex are in pixels, with (0, 0) being the top-left cornerofin, and with y increasing down the image. Usevips_xyz() to build indeximages.

interpolate defaults to bilinear.

By default, new pixels are filled withbackground. This defaults tozero (black). You can set other extend types withextend.VIPS_EXTEND_COPYis better for image upsizing.

Image are normally treated as unpremultiplied, so this operation can be useddirectly on PNG images. If your images have been throughvips_premultiply(),setpremultiplied.

This operation does not change xres or yres. The image resolution needs tobe updated by the application.

Seevips_maplut() for a 1D equivalent of this operation.

See also:vips_xyz(),vips_affine(),vips_resize(),vips_maplut(),VipsInterpolate.

[method]

vips_quadratic ()

intvips_quadratic (VipsImage *in,VipsImage **out,VipsImage *coeff,...);

Optional arguments:

This operation is unfinished and unusable, sorry.

See also:vips_affine().

[method]

enum VipsKernel

The resampling kernels vips supports. Seevips_reduce(), for example.

enum VipsSize

Controls whether an operation should upsize, downsize, both up anddownsize, or force a size.

See also:vips_thumbnail().