Canvas Size Transparency


Today’s Question: I used to use the crop tool to extend the canvas and fill with white or black as I needed. Lately, when I extend the canvas, I only see a transparent area, not a pixel area. I have to then create a layer under it and fill with white. Is there a setting that needs resetting?

Tim’s Quick Answer: When extending the overall dimensions of an image using the Canvas Size command, you will see transparent pixels in the new area if there is no Background image layer. Only if there is an actual Background image layer will the new pixels created by the Canvas Size command actually contain pixels rather than transparency.

More Detail: This is in some respects a matter of semantics, since transparent areas of an image will show up as white pixels in most contexts. However, you can ensure that the new area being added via the Canvas Size command contains “real” pixels by making sure you have a Background image layer.

To convert your primary image layer to a Background layer, you first need to select the applicable image layer on the Layers panel. You can do so by simply clicking on the thumbnail for that layer. Then go to the menu bar and choose Layer > New > Background from Layer. This will convert the current layer to a Background image layer, which in turn will cause the Canvas Size command to add pixels rather than transparency for the new area of the image.

It is worth noting that if you turn off the “Delete Cropped Pixels” checkbox on the Options bar when working with the Crop tool, the image you crop will no longer have a Background image layer once the crop is applied. In theory you might want to instead turn on the “Delete Cropped Pixels” checkbox to avoid this issue. However, it is important to keep in mind that having this option turned off can greatly increase your flexibility as you are fine-tuning the final effect for a given photo.