A PICT file is a standard Macintosh image file format and can be either a raster image or a vector image, depending on the program that created it. PSD signifies an Adobe Photoshop graphic file. On your computer screen, digital images are modern-day optical illusions. The images you see are actually composed of tiny, black, white, gray or colored squares. These squares are packed so closely together that your mind blends them into continuous tones to form realistic looking images.
Image resolution refers to the spacing of pixels in the image.
The more pixels per square inch, the sharper an image is and the smoother the blend between colors. Your image should contain no more dpi than your medium can display . If you will display your image in a Power Point presentation, you should save your image with a resolution of 100 dpi . If you will display your image on the web, you should save your image with a resolution of 72 dpi TIP Resolution is connected to the file size of the image. Images with high resolution have a large file size .