Today’s Question: When I’m changing the resolution of a photo in the Image Size dialog in Photoshop, I’m not able to select the Pixels option for the Width or Height. How can I resize based on specific pixel dimensions rather than using another option such as inches?
Tim’s Quick Answer: To enable the Pixels option from the popup for Width or Height in the Image Size dialog in Photoshop you need to turn on the Resample checkbox. Note that this checkbox always needs to be turned on to be able to change the pixel dimensions for an image.
More Detail: As odd as it may sound, in the Image Size dialog it is possible to change the output size of an image without actually changing the pixel dimensions for the image. This is why you need to have the Resample checkbox turned on to be able to adjust the image size based on pixels rather than a different unit of measure such as inches or centimeters.
If the Resample checkbox is turned off the pixel dimensions for the image can’t be changed. Instead, if you for example change the dimensions of the image in inches, the pixel per inch resolution will be adjusted accordingly, so that the same number of pixels remain in the image. In most cases, however, you would want to resize the actual pixel dimensions if you’re preparing an image to be shared at a particular size.
With the Resample checkbox turned off, you aren’t changing the number of pixels in the image, so instead making a change to either the dimensions or the resolution will cause the other value to update accordingly, so the same number of pixels remain. In this case the Pixels option is disabled on the popup for Width and Height because you’re not able to change the pixel dimensions.
If you turn on the Resample checkbox, you’re able to alter the pixel dimensions, so the Pixels option will be enabled on the popups. This can be helpful when resizing an image for digital output, such as sizing based on the resolution of a digital projector. For output such as a print, it is generally easier to specify the dimensions in inches or centimeters, along with designating the pixel per inch (or centimeter) resolution based on the capabilities of the printer being used.
