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int | vips_shrink () |
int | vips_shrinkh () |
int | vips_shrinkv () |
int | vips_reduce () |
int | vips_reduceh () |
int | vips_reducev () |
int | vips_similarity () |
int | vips_affine () |
int | vips_resize () |
int | vips_mapim () |
int | vips_quadratic () |
There are three types of operation in this section.
First, vips_affine()
applies an affine transform to an image. This is any
sort of 2D transform which preserves straight lines; so any combination of
stretch, sheer, rotate and translate. You supply an interpolator for it to
use to generate pixels, see vips_interpolate_new()
. It will not produce
good results for very large shrinks.
Next, vips_resize()
specialises in the common task of image reduce and
enlarge. It strings together combinations of vips_shrink()
, vips_reduce()
,
vips_affine()
and others to implement a general, high-quality image
resizer.
Finally, vips_mapim()
can apply arbitrary 2D image transforms to an image.
int vips_shrink (VipsImage *in
,VipsImage **out
,double hshrink
,double vshrink
,...
);
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_affine()
plus bilinear interpolation 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_affine()
.
int vips_shrinkh (VipsImage *in
,VipsImage **out
,int hshrink
,...
);
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()
.
int vips_shrinkv (VipsImage *in
,VipsImage **out
,int vshrink
,...
);
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()
.
int vips_reduce (VipsImage *in
,VipsImage **out
,double hshrink
,double vshrink
,...
);
Optional arguments:
kernel
: VipsKernel to use to interpolate (default: lanczos3)
centre
: gboolean
use centre rather than corner sampling convention
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 centre
to use centre rather than corner sampling convention. Centre
convention can be useful to match the behaviour of other systems.
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_affine()
.
int vips_similarity (VipsImage *in
,VipsImage **out
,...
);
Optional arguments:
scale
: gdouble
, scale by this factor
angle
: gdouble
, rotate by this many degrees clockwise
interpolate
: VipsInterpolate, interpolate pixels with this
idx
: gdouble
, input horizontal offset
idy
: gdouble
, input vertical offset
odx
: gdouble
, output horizontal offset
ody
: gdouble
, output vertical offset
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.
int vips_affine (VipsImage *in
,VipsImage **out
,double a
,double b
,double c
,double d
,...
);
Optional arguments:
interpolate
: VipsInterpolate, interpolate pixels with this
oarea
: VipsArrayInt, output rectangle
idx
: gdouble
, input horizontal offset
idy
: gdouble
, input vertical offset
odx
: gdouble
, output horizontal offset
ody
: gdouble
, output vertical offset
This operator performs an affine transform on an image using interpolate
.
The transform is:
X = a
* (x + idx
) + b
* (y + idy
) + odx
Y = c
* (x + idx
) + d
* (y + idy
) + doy
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.
interpolate
defaults to bilinear.
idx
, idy
, odx
, ody
default to zero.
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.
int vips_resize (VipsImage *in
,VipsImage **out
,double scale
,...
);
Optional arguments:
vscale
: gdouble
vertical scale factor
kernel
: VipsKernel to reduce with
centre
: gboolean
use centre rather than corner sampling convention
Resize an image.
When downsizing, the
image is block-shrunk with vips_shrink()
,
then the image is shrunk again to the
target size with vips_reduce()
. How much is done by vips_shrink()
vs.
vips_reduce()
varies with the kernel
setting.
vips_resize() normally uses VIPS_KERNEL_LANCZOS3 for the final reduce, you
can change this with kernel
.
Set centre
to use centre rather than corner sampling convention. Centre
convention can be useful to match the behaviour of other systems.
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.
vips_resize() normally maintains the image apect ratio. If you set
vscale
, that factor is used for the vertical scale and scale
for the
horizontal.
This operation does not change xres or yres. The image resolution needs to be updated by the application.
See also: vips_shrink()
, vips_reduce()
.
int vips_mapim (VipsImage *in
,VipsImage **out
,VipsImage *index
,...
);
Optional arguments:
interpolate
: interpolate pixels with this
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:
1 |
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.
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.
int vips_quadratic (VipsImage *in
,VipsImage **out
,VipsImage *coeff
,...
);
Optional arguments:
interpolate
: use this interpolator (default bilinear)
This operation is unfinished and unusable, sorry.
See also: vips_affine()
.
The resampling kernels vips supports. See vips_reduce()
, for example.
The Lanczos kernels vary in size with the downsampling ratio.