Pixelization can turn even the most beautiful images into a digital mess. Pixels are the square or rectangular units that make up a digital image. Pixelation is a result of expanding an image beyond its capacity, for example, if you were to take a thumbnail-sized image and blow it up to the equivalent of an 8-inch by 11-inch photo. Pixelation indicates a limit on the information available in an image, which makes it impossible to create a perfect image from one. Photo-editing software makes it possible to improve the photo's clarity.
Load the image into your photo-editing software.
Use a blur filter such as Gaussian Blur to smooth out all the harsh edges of the pixels. Experiment with various settings of the filter. For example, increase the number of pixels the filter averages.
Apply a sharpen filter such as Smart Sharpen to fix any excessive blurriness that results from blur filters. The program will attempt to sharpen the edges in the picture and make the subjects clearer.
Create a separate copy of the original image and use that one to experiment with the artistic filters. For example, the Cutout Filter can turn a pixilated image of a waterfall into one that looks like a long exposure image where layers of silky water are falling over the rocky edge.
Experiment with this filter and various settings and you might be able to produce an image that you like. Turn on "Auto Save" or remember to save your work every 10 minutes, especially if you've made a lot of changes in that time.
Save a backup copy of the original image in case you don't like some changes you make. Do not overdo it with the sharpening filter. It can make the image look harsh.