What is the difference between canvas size and image size?
Answer: When working with an image-editing program, such as Adobe Photoshop, you can modify both the image size and canvas size of an image. While they sound similar, they modify the image in two different ways.
When you modify the canvas size of an image, you either increase or decrease the amount of area of the image canvas. This means that adding to the canvas size will add blank area around the image (or fill it with the background color if there is only one layer). Conversely, if you decrease the canvas size, the image will be cropped, meaning you will lose some of the image depending on where you crop it.
When you modify the image size of an image, you change how large the image is. When you increase the image size, the image will appear bigger, and may become blocky or blurry if increased too much. Decreasing the image size will shrink the image, and may cause some detail to be lost. When you change the image size, you can also modify the image resolution (in DPI), and stretch the image by unchecking the "Constrain Proportions" box. Unlike changing the canvas size, when you change the image size, the original image still fills the whole window.
So if you want to add more area to an image or crop a section of it, change the canvas size. If you want to shrink, expand, or change the resolution of an image, adjust the image size.