A composite operation combines pixels from a different image with your
target image. You can control composition by choosing which image to combine,
where the combining occurs (the offset from the target image), and
how the pixels are combined (composite operation).
Select your composite image, press Browse to browse and select
your image file or enter the URL of your
image. Use clipboard: as the filename to import a previously
saved image from the ImageMagick Studio clipboard.
The offset geometry specifies the (x,y) offset from your target image to
combine the composite image. The x and y offset are conveniently specified
as one value. For example, to offset the target image by 30 pixels in the
horizontal direction and 40 pixels in the vertical use:
+30+40
For convenience, you can select a gravity instead of an offset geometry.
For example, Center centers the image. The location geometry
has precedence over any gravity.
Finally, you need to specify how the pixels are combined.
By default, each of the composite image pixels are
replaced by the corresponding image tile pixel. You can
choose an alternate composite operation.
How each operator behaves is described below.
- over
- The result will be the union of the two image shapes, with
composite image obscuring image in the region of overlap.
- in
- The result is simply composite image cut by the shape of
image. None of the image data of image will be in the
result.
- out
- The resulting image is composite image with the shape of
image cut out.
- atop
- The result is the same shape as image image, with
composite image obscuring image where the image shapes
overlap. Note this differs from over because the portion of
composite image
outside image's shape does not appear in the result.
- xor
- The result is the image data from both composite image and
image that is outside the overlap region. The overlap region
will be blank.
- plus
- The result is just the sum of the image data. Output values are cropped
to 255 (no overflow). This operation is independent of the matte
channels.
- minus
- The result of composite image - image, with underflow
cropped to zero. The matte channel is ignored (set to 255, full coverage).
- add
- The result of composite image + image, with overflow
wrapping around (mod 256).
- subtract
- The result of composite image - image, with underflow
wrapping around (mod 256). The add and subtract
operators can be used to perform reversible transformations.
- difference
- The result of abs(composite image - image). This is
useful for comparing two very similar images.
- multiply
- The result of composite image * image. This is
useful for the creation of drop-shadows.
- bumpmap
- The result of image shaded by image.
- replace
- The resulting image is image replaced with
composite image. Here the matte information is ignored.
The image compositor requires a matte, or alpha channel in the
image for some operations. This extra channel usually
defines a mask which represents a sort of a cookie-cutter for the image. This
is the case when matte is 255 (full coverage) for pixels inside the shape, zero
outside, and between zero and 255 on the boundary. For certain operations,
if image does not have an matte channel, it is initialized with 0 for
any pixel matching in color to pixel location (0,0), otherwise 255.
properly borderwidth must be 0).