Canvas Size
Changing Canvas Size

Clive R. Haynes FRPS

To change canvas dimensions, go via:
Image > Adjust > Canvas Size

However, this tends to be a little confusing at first.

Changing the canvas size creates additional space to work in as extra pixels are added to the total picture area (the ‘canvas’ is part of this) - this increases file size.

Remember: once the canvas size has been changed the whole area, that is the so-called 'canvas' and the original picture content all now become the new image size and from this point (unless changed again) both image size and canvas size will be the same.

Reducing canvas size will chop / crop into the image area – the program will warn you about this and ask if you wish to proceed.

Placing the Image in the Canvas Area
Having made the decision about the dimensions of the canvas, you can decide where the extended canvas will be in relation to the original image.
Use the nine rectangle in the dialogue box to determine this. Click on the square that places the image in the canvas area as you broadly require. This is setting the 'Anchor Point'. You can move the picture afterwards (providing the Layer isn't 'locked').
If you do nothing, then the image will appear in the centre of the canvas.

Above:
The nine squares, which represent the 'Anchor Points' for the image. The additional canvas will extend into the grey area. Once 'OK' is clicked, then the whole area (canvas and all) becomes the new image size.

Photoshop CS includes the 'Relative' tick-box. When ticked, this allows the amount of extra canvas size required to be typed into the width & height boxes rather than the total amount - a useful option.

The Colour of the 'Canvas'
When expanding Canvas Size in earlier editions of Photoshop, the extra Canvas Space always adopted the Background Colour for the image. It was therefore important to ensure that the Background Colour was as you wished before opening the Canvas Size dialogue box.
Photoshop CS introduced an extra option - the ability to choose the Canvas Colour from within the dialogue box - another very useful option.

Canvas as a 'Border'
Adding Canvas Size effectively places a border around your image - indeed this is a simple way of adding a border