The Canvas Size command in the Image menu allows you to alter the dimensions of an image. However, unlike the Image Size command, this is done without changing the resolution. In effect, when the width or height is reduced the image is cropped, and when it is increased transparent pixels are added to fill up the extra space. (Note that the image canvas is usually surrounded by a gray area if the canvas is smaller than the image window. This gray area is inaccessible to the Photopaint tools. Increasing the canvas size creates a newly accessible area, hence allowing you to add a caption, say, to the bottom of a scanned photograph.)
In the "Canvas Size" dialog you can make changes in the Width and Height boxes. Note that the amount of space required for the image is shown just above.
In the Anchor box there is a grid of nine squares which helps you to choose where the image will be located on a resized canvas. Since changing the canvas size results in either a cropping or expansion of the canvas, there are two basic uses of the anchor grid:
Use the grid to preserve a part of the image when cropping. For instance, if you are reducing the height by two units (of some scale) but wish to preserve the bottom of the image, you should click one of the bottom squares to ensure that the two units are cropped from the top of the image. Clicking on one of the middle (horizontal line of) squares will result in one unit being cropped from the top and one from the bottom of the image. The same principles can be applied to cropping from the left and right sides of the image. (Note that you can also crop using the Crop tool on the Tools bar - see Crop.)
Use the grid to determine where in an expanded canvas the original image should appear. For instance, if you are adding two units to the width and height of the canvas and you would like these to be distributed evenly around the image, then click on the center square to create a one-unit band around the image. If you click the lower-left square, two units are added to the top and two to the right side of the image.
Once you are satisfied with the width, height and anchor grid setting click on OK to implement the changes.
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