The “canvas” is the visible area of the image. By default
the size of the canvas coincides with the size of the layers. The
Canvas Size command lets you enlarge or
reduce the canvas size without modifying the contents of the layers in
the image. When you enlarge the canvas, you create free space around
the contents of the image. When you reduce it, the visible area is
cropped, however the layers still extend beyond the canvas border.
Activating the Command
You can access this command from the image menubar through
Description of the “Canvas size” dialog
The “Canvas size” dialog
You can set the Width and the
Height of the canvas. The default
units are pixels but you can choose different units, e.g.
percent, if you want to set the new dimensions relative to the
current dimensions. If the Chain to the right of the Width and
Height is not broken, both Width and Height keep the same
relative size to each other. That is, if you change one of the
values, the other one also changes a corresponding amount.
If you break the Chain by clicking on it, you can set
Width and Height separately.
Whatever units you use, information about the size in pixels
and the current resolution are always displayed below the
Width and Height
fields. You cannot change the resolution in the
Canvas Size dialog; if you want to
do that, use the Print
The Offset values are used to place the image
on the canvas. The preview window displays the image in a frame with
a thin border. When the canvas is smaller than the image, the
preview window shows it in a frame with a thin black border.
The X and Y
parameters specify the coordinates of the upper left
corner of the image relative to the upper left corner of
the canvas. When the canvas is smaller than the image, the X and
Y values are negative. You can change these values by using the
text boxes. The default units are pixels, but you can choose
different units. By clicking on the arrows next to the text
boxes, you can move the image one pixel at a time. You can
move the image ten pixels at a time by clicking on the arrows
while pressing the Shift key.
The Center button allows you to center the
image on the canvas. When you click on the Center button,
the offset values are automatically calculated and displayed in
the text boxes.
When you click on the Resize button,
the canvas is resized, but the pixel information and the drawing
scale of the image are unchanged.
If the layers of the image did not extend beyond the borders of
the canvas before you changed its size, there are
no layers on the part of the canvas that was added by resizing it.
Therefore, this part of the canvas is transparent and displayed
with a checkered pattern, and it is not immediately available for
painting. You can either
the image, in which case you will get an image with a single layer
that fits the canvas exactly, or you can use the
Layer to Image Size
command to resize only the active layer, without changing any other
layers. You can also create a new layer and fill it with the
background you want. By doing this, you create a
digital “passe-partout” (a kind of glass mount
with a removable back for slipping in a photograph).