How to Increase the Size of a Photo Without Losing Its Resolution
There are many occasions when you might want to enlarge an image, such as when creating a large ad for a banner or a sign. But losing resolution often occurs when enlarging images. This happens because photos are made up of small dots, and when you enlarge the image you make the dots large enough to be visible. To solve this problem you need to use a good graphics program like Photoshop that uses interpolation to divide the dots as images enlarge. If you don't have access to Photoshop, you can instead use the freeware graphics program GIMP, which has similar tools and capabilities.
Load the picture you want to use onto your computer, either by transferring it from a camera or from a digital media like a CD or flash drive. To ensure having a better quality image, don't scan the image in.
Open your graphics program, and then select “File” from the menu and click “Open.” In the dialog that pops up browse to the image you loaded and open it.
Select “Image” from the menu and click “Image Size” (in GIMP select "Scale Image"). In the dialog box that opens change the “Interpolation” method at the bottom to “ Bicubic Smoother." Then increase the width and height of the image to the size you want for your project. If your version of Photoshop lacks “Bicubic Smoother” as an option or if you are using GIMP, then select “Bicubic” and gradually increase the size in 10 percent increments, clicking “OK” for each increase.
Select “File” and select “Save As.” Name your file and select JPEG as the file type.