libvips

vips_shrink ()

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

Optional arguments:

Shrink in by a pair of factors with a simple box filter. For non-integer factors, vips_shrink() will first shrink by the integer part with a box filter, then use vips_reduce() to shrink by the remaining fractional part.

This is a very low-level operation: see vips_resize() for a more convenient way to resize images.

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

See also: vips_resize(), vips_reduce().

[method]

vips_shrinkh ()

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

Optional arguments:

Shrink in horizontally by an integer factor. Each pixel in the output is the average of the corresponding line of hshrink pixels in the input.

This is a very low-level operation: see vips_resize() for a more convenient way to resize images.

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

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

[method]

vips_shrinkv ()

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

Optional arguments:

Shrink in vertically by an integer factor. Each pixel in the output is the average of the corresponding column of vshrink pixels in the input.

This is a very low-level operation: see vips_resize() for a more convenient way to resize images.

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

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

[method]

vips_reduce ()

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

Optional arguments:

Reduce in by a pair of factors with a pair of 1D kernels. This will not work well for shrink factors greater than three.

Set gap to speed up reducing by having vips_shrink() to shrink with a box filter first. The bigger gap , the closer the result to the fair resampling. The smaller gap , the faster resizing. The default value is 0.0 (no optimization).

This is a very low-level operation: see vips_resize() for a more convenient way to resize images.

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

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

[method]

vips_reduceh ()

int
vips_reduceh (VipsImage *in,
              VipsImage **out,
              double hshrink,
              ...);

Optional arguments:

Reduce in horizontally by a float factor. The pixels in out are interpolated with a 1D mask generated by kernel .

Set gap to speed up reducing by having vips_shrinkh() to shrink with a box filter first. The bigger gap , the closer the result to the fair resampling. The smaller gap , the faster resizing. The default value is 0.0 (no optimization).

This is a very low-level operation: see vips_resize() for a more convenient way to resize images.

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

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

[method]

vips_reducev ()

int
vips_reducev (VipsImage *in,
              VipsImage **out,
              double vshrink,
              ...);

Optional arguments:

Reduce in vertically by a float factor. The pixels in out are interpolated with a 1D mask generated by kernel .

Set gap to speed up reducing by having vips_shrinkv() to shrink with a box filter first. The bigger gap , the closer the result to the fair resampling. The smaller gap , the faster resizing. The default value is 0.0 (no optimization).

This is a very low-level operation: see vips_resize() for a more convenient way to resize images.

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

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

[method]

vips_thumbnail ()

int
vips_thumbnail (const char *filename,
                VipsImage **out,
                int width,
                ...);

Optional arguments:

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

See vips_thumbnail_buffer() to thumbnail from a memory buffer, or vips_thumbnail_source() to thumbnail from an arbitrary byte source.

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

The output image will fit within a square of size width x width . You can specify a separate height with the height option. Set either width or height to a very large number to ignore that dimension.

If you set crop , then the output image will fill the whole of the width x height rectangle, with any excess cropped away. See vips_smartcrop() for details on the cropping strategy.

Normally the operation will upsize or downsize as required to fit the image inside or outside the target size. If size is set to VIPS_SIZE_UP, the operation will only upsize and will just copy if asked to downsize. If size is set to VIPS_SIZE_DOWN, the operation will only downsize and will just copy if asked to upsize. If size is VIPS_SIZE_FORCE, the image aspect ratio will be broken and the image will be forced to fit the target.

Normally any orientation tags on the input image (such as EXIF tags) are interpreted to rotate the image upright. If you set no_rotate to TRUE, these tags will not be interpreted.

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

If you set export_profile to the filename of an ICC profile, the image will be transformed to the target colourspace before writing to the output. You can also give an import_profile which will be used if the input image has no ICC profile, or if the profile embedded in the input image is broken.

Use intent to set the rendering intent for any ICC transform. The default is VIPS_INTENT_RELATIVE.

Use fail_on to control the types of error that will cause loading to fail. The default is VIPS_FAIL_ON_NONE, ie. thumbnail is permissive.

See also: vips_thumbnail_buffer().

vips_thumbnail_buffer ()

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

Optional arguments:

Exactly as vips_thumbnail(), but read from a memory buffer. One extra optional argument, option_string , lets you pass options to the underlying loader.

See also: vips_thumbnail().

vips_thumbnail_image ()

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

Optional arguments:

Exactly as vips_thumbnail(), but read from an existing image.

This operation is not able to exploit shrink-on-load features of image load libraries, so it can be much slower than vips_thumbnail() and produce poorer quality output. Only use it if you really have to.

See also: vips_thumbnail().

[method]

vips_thumbnail_source ()

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

Optional arguments:

Exactly as vips_thumbnail(), but read from a source. One extra optional argument, option_string , lets you pass options to the underlying loader.

See also: vips_thumbnail().

vips_similarity ()

int
vips_similarity (VipsImage *in,
                 VipsImage **out,
                 ...);

Optional arguments:

This operator calls vips_affine() for you, calculating the matrix for the affine transform from scale and angle . Other parameters are passed on to vips_affine() unaltered.

See also: vips_affine(), VipsInterpolate.

[method]

vips_rotate ()

int
vips_rotate (VipsImage *in,
             VipsImage **out,
             double angle,
             ...);

Optional arguments:

This operator calls vips_affine() for you, calculating the matrix for the affine transform from scale and angle . Other parameters are passed on to vips_affine() unaltered.

See also: vips_affine(), VipsInterpolate.

[method]

vips_affine ()

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

Optional arguments:

This operator performs an affine transform on an image using interpolate .

The transform is:

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X = @a * (x + @idx) + @b * (y + @idy) + @odx
Y = @c * (x + @idx) + @d * (y + @idy) + @doy

where:
  x and y are the coordinates in input image.
  X and Y are the coordinates in output image.
  (0,0) is the upper left corner.

The section of the output space defined by oarea is written to out . oarea is a four-element int array of left, top, width, height. By default oarea is just large enough to cover the whole of the transformed input image.

By default, new pixels are filled with background . This defaults to zero (black). You can set other extend types with extend . VIPS_EXTEND_COPY is 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 used directly on PNG images. If your images have been through vips_premultiply(), set premultiplied .

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

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

[method]

vips_resize ()

int
vips_resize (VipsImage *in,
             VipsImage **out,
             double scale,
             ...);

Optional arguments:

Resize an image.

Set gap to speed up downsizing by having vips_shrink() to shrink with a box filter first. The bigger gap , the closer the result to the fair resampling. The smaller gap , the faster resizing. The default value is 2.0 (very close to fair resampling while still being faster in many cases).

vips_resize() normally uses VIPS_KERNEL_LANCZOS3 for the final reduce, you can change this with kernel . Downsizing is done with centre convention.

When upsizing (scale > 1), the operation uses vips_affine() with a VipsInterpolate selected depending on kernel . It will use VipsInterpolateBicubic for VIPS_KERNEL_CUBIC and above. It adds a 0.5 pixel displacement to the input pixels to get centre convention scaling.

vips_resize() normally maintains the image aspect ratio. If you set vscale , that factor is used for the vertical scale and scale for the horizontal.

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

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

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

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

[method]

vips_mapim ()

int
vips_mapim (VipsImage *in,
            VipsImage **out,
            VipsImage *index,
            ...);

Optional arguments:

This operator resamples in using index to look up pixels. out is the same size as index , with each pixel being fetched from that position in in . That is:

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

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

Coordinates in index are in pixels, with (0, 0) being the top-left corner of in , and with y increasing down the image. Use vips_xyz() to build index images.

interpolate defaults to bilinear.

By default, new pixels are filled with background . This defaults to zero (black). You can set other extend types with extend . VIPS_EXTEND_COPY is better for image upsizing.

Image are normally treated as unpremultiplied, so this operation can be used directly on PNG images. If your images have been through vips_premultiply(), set premultiplied .

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

See vips_maplut() for a 1D equivalent of this operation.

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

[method]

vips_quadratic ()

int
vips_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. See vips_reduce(), for example.

enum VipsSize

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

See also: vips_thumbnail().