How to Change the Dimensions of PNG Pictures
The Portable Network Graphics image format is a compressed image format that reduces the size of a bitmapped image without removing data permanently, as is the case with the JPG image format. The PNG format works well for screenshots of computer applications and other types of images that contain large blogs of solid color. The Microsoft Paint application in Windows 7 has support for the PNG format. If you have taken a screenshot and need to reduce its size for distribution on the Internet, you can use Paint to change its dimensions.
Open the Start menu, and type "Paint" in the search field at the bottom. Click the "Paint" icon when it appears on the result list to launch the Microsoft Paint application.
Drag the PNG file that you want to resize into the open Paint window, and drop it. Alternatively, click the blue button in the upper-left corner of the window and select "Open." Locate the PNG file on your computer and double-click it.
Click the "Home" tab at the top of the window, and then click the "Resize" button in the "Image" section of the toolbar.
Click the "Percentage" radio button at the top of the window to change the dimensions of the image as a relative percentage of its current size, or click the "Pixels" radio button to specify a new size in pixels.
Click the "Maintain aspect ratio" check box if you would like Paint to change one of the image's dimensions automatically when you change the other to maintain the height-to-width ratio.
Click the field next to "Horizontal," and type a percentage or value in pixels to change the horizontal dimensions of the image. If you did not click the "Maintain aspect ratio" check box, repeat this step with the "Vertical" field to change the vertical dimensions of the image.
Click "OK" to resize the image.
Click the floppy disk icon at the top of the window to save the image.