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The “canvas” is the visible area of the image. By default
the size of the canvas coincides with the size of the layers. The
command lets you enlarge or
reduce the canvas size. You can, if you want, modify the size of the
layers. 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.
When you reduce the canvas size, the new canvas appears surrounded with
a thin negative border in the preview. The mouse pointer is a moving
cross: click and drag to move the image against this frame.
6.11.1. Activating the Command
6.11.2. Description of the “Canvas size” dialog
Canvas Size
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Width; Height
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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
dialog; if you want to
do that, use the Print
Size dialog.
Offset
The Offset values are used to place the image
(the image, not the active layer) on the canvas. You can see the
size and the content of the canvas in the preview of the dialog
window. When the canvas is smaller than the image, the preview window
shows it in a frame with a thin negative border.
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X ; Y
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The X and Y specify the
coordinates of the upper left corner of the image relative to the
upper left corner of the canvas. They are negative when the
canvas is smaller than the image. You can place the image in
different ways (of course, the coordinates can't exceed the
canvas borders):
-
by click-and-dragging the image,
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by entering values in the X and
Y text boxes,
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by clicking on the small arrow-heads. This increments the
value by one pixel (unit).
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And when the focus is on a text box, you can use the
keyboard arrow keys, Up and
Down to change by one pixel (unit), or
PageUp and PageDown to
change the value by 10 pixels (units).
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Layers
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Before the GIMP-2.4 version, “Canvas Size” had no
influence on layer size. To change it, you had to use the Layer Boundary Size command.
The “Layers” option now allows you to specify how,
possibly, layers will be resized. The drop-down list offers you
several possibilities:
-
None: default option. No layer is
resized, only the canvas is.
-
All Layers: all layers are resized to
canvas size.
-
Image-sized layers: only layers with
the same size as the image are sized to canvas size.
-
All visible layers: only visible
layers, marked with a
icon, in the Layer Dialog, are sized to canvas size.
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All linked layers: only linked layers,
marked with a
in the Layer Dialog, are sized to canvas size.
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Center
-
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.
![[Note]](images/note.png)
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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
flatten
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).
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6.11.4. What's Canvas Size useful for?
You can use this command to crop an image:
Click on the chain next to Width and Height entries to unlink
dimensions. By modifying these dimensions and moving image against
canvas, by trial and error, you can crop the part of the image you
want. Click on the Center button and then on the Resize button.
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