I Have a jpg image which is about five inches square at 500dpi. I would like to enlarge the image as far as possible keeping the resolution suitable for print at 300dpi.
I Have tied adjusting the resolution but the image reduces in size . Do I need to enlarge the image first ? I am unsure by how much. Or is there a button which will do it for me? Thank you.
When you choose Image > Image Size, if it shows Width and Height 5 inches and the resolution of 500 pixels/inch, when you uncheck Resample Image box and for Resolution type 300 this will increase the size to 8.333 inches per side which is the maximum size you can get with 300 ppi without using interpolation (changing the number of pixels shown in the Pixel Dimension section of the Image Size window).
You can increase the size further using interpolation which is what happens when the Resample Image box is checked. For increasing the size you can choose Bicubic Smoother (best for enlargements) from the menu at the bottom of the Image Size window. But how good the result will be depends on the enlargement, the viewing distance of the printed image, your standards, and the details on the image itself - for example if it is an image of a foggy environment the size can be increased much more without noticeable loss of details as opposed to an image with details with sharp contrast.