How Do I Change the Number of Pixels in a Picture?

Computer and print images are made up of tiny dots known as "picture elements" or pixels. The size of an image is measured by the number of pixels along the width of the image times the number along the height, such as 1024 x 768. You can make an image larger or smaller by changing the number of pixels. There are limits, however, to how much you can resize an image without losing quality.

The resolution of an image refers to the number of pixels per inch (ppi). The higher the resolution, the larger the image will be when printed at true size. You can change the resolution of an image by modifying the number of pixels using a graphics editor like Microsoft Paint. In Paint, the Resize command is used to access the Resize Image pane, where you can specify new width and height dimensions in pixels.

The term aspect ratio refers to the relationship of the width to the height of an image. When you change the number of pixels in an image using Paint, you can turn on a toggle to make sure the aspect ratio of the image remains the same. Each time you change the pixel count for the width, the height will automatically update to maintain the same aspect ratio, and vice-versa for changing the height. If you want to change the aspect ratio on purpose, turn off the toggle and the pixel count fields can be changed independently.

Increasing or decreasing the number of pixels in an image changes its resolution. Since the number of pixels per inch changes, the print size of the image also changes. Adding pixels will increase the print size, while removing pixels will decrease it. In general, you can usually decrease the pixels in an image without losing image quality. However, if you try to increase the pixels by a large amount the quality will most likely suffer. This is because extra pixels need to be created automatically by the graphics editor through a process known as interpolation. The resulting image can be blurred or distorted.

The best resolution for any image depends in large part on what you plan to do with it. To ensure you have the highest quality images for your needs, set the pixel resolution on your camera before taking pictures. If file storage on your device is an issue, lower resolution images generally require less storage. It often makes sense to take lower resolution pictures to accommodate device storage rather than trying to change the image resolution later.

The size of an image file is proportional to its pixel dimensions. A higher number of pixels can give an image greater in detail, but it also means a larger file is stored. If you want to make a large image file smaller, changing the number of pixels is not the only solution. On both Windows and Mac, you can make a file smaller with the zip compression utility. When you select the file and then use the zip command, a compressed version of the file is created. You can send this version as an attachment through email when the original image is too large. The recipient can use the zip utility to uncompress, or unzip, the file and access the original.

Cropping is the operation of removing portions from around the edges of an image. Most graphic editor software programs, including Paint, allow you to crop images. If you want to reduce the number of pixels in an image and there are parts of the image you don't need, then cropping may be the best way to decrease the pixel count.