Putting It All Together - Some Simple Principles

If we know the pixel dimensions of an image, we know the megapixel resolution. Example: if an image's pixel dimensions are 2048x1536, we multiply 2048x1536 and get 3,145,728, just over 3 million pixels. This is a 3 megapixel image.

If we know the pixel dimensions and the set print resolution (the "dpi resolution"), we know what the physical size of the print will be. Example: if the same 2048x1536 image is set to print at 300ppi, the resulting print will be 6.8x5.1 (roughly a 5x7 print). We just divided each of the pixel dimensions by the print resolution to yield the physical dimensions of the resultant print.

If we know the required print resolution for photo quality on our printer, and the desired print size, we know the minimum requisite image resolution. Example: if we need to print at 300ppi, and we want our print to be 8x10, we multiply the desired print dimensions by the requisite print resolution and get the minimum requisite image resolution, 2400x3000.

If we wanted to make a 8x10 print from a 35mm frame, and we need to print at 300ppi for best results on our inkjet printer, we know we will need digital image pixel dimensions of at least 2400x3000. Knowing the physical size of the 35mm frame is slightly less than 1x1.5 inches, we can determine we would need to scan the film at 2400ppi or higher capture resolution. The Kodak Photo CD would fall short at 2048x3072.

If we want to use our images on computer monitors, we must know the monitor resolution or assume a common resolution we want to target for best results. If we assume most users will be utilizing screen resolutions of 1024x768, we would want to make our image resolution (pixel dimensions) 1024x768 for desktop wallpaper or full screen display. For e-mail use, we would want to make them smaller, maybe half size - 512x384.