The only two values you can change are the physical size (Width and Height in Document Size) or the resolution (pixels/inch). When you deselect, or turn off, Resample, the pixel dimension fields are not available. No data is added to or removed from the image. Resizing without resampling changes the image's physical size without changing the pixel dimensions in the image. When you resize an image and do not resample it, you change the image's size without changing the amount of data in that image. Degraded images can look blurry, jagged, or blocky.
For example, if the file size changes from 250 KB to 500 KB, you add twice as much data to the image, which can degrade it. Then, you can use the file size information to understand how much data is removed or added to your image when you resample it. Note the file size value before you change the other values in the dialog box. You cannot set the file size it changes when you change the total amount of data in the image (the pixel dimensions).
Pixel dimensions = physical size / resolution.Resolution = physical size / pixel dimensions.Physical size = resolution x pixel dimensions.Photoshop calculates the physical size, resolution, and pixel dimensions of an image as follows: Image resolution when printed: This value appears in pixels per inch or pixels per centimeter.Document size: Physical size of the image when printed, including a width and height.Image size when it's open in Photoshop: This value appears at the top of the dialog box.
Pixel dimensions: The width and height of the image.When you use the Image Size dialog to resize your images (choose Image > Image Size), four aspects of your image can change: