January Newsletter
Greetings from
Porter's Camera Store!

Pixels are to digital images what silver halides are to film. Pixels (short for picture elements) are the small sections of color and/or tone that together form a digital image. Pixels form an image like pieces of a mosaic. When the pixels are viewed in a group, an image is formed. When there are enough pixels and they are small enough so as not to be individually discernible, the digital image can achieve photo quality. Increased magnification of any digital image will eventually show the individual pixels.

Your digital camera records pixels, your scanner converts physical images into pixels, your photo editing software manipulates pixels, your computer monitor displays pixels, and your printer paints pixels onto paper. In the digital world, "inches" don't exist, only pixels do.

A digital image as it is created by a digital camera or scanner, is simply an informational record of a grid of pixels - a map of specific tones at specific locations called a bitmap. The image, as it is, has no physical size. Only when an image is displayed, does it take on physical form. When it is displayed on a monitor or printed on paper, the physical image has dimensions of width and height.

The key to successfully editing, scanning, and printing images lies in understanding how pixels transform into inches and vice versa. The interpreter between the physical world of inches and the digital world of pixels is resolution. When you print an image, the printer translates pixels into inches using resolution.

So what resolution setting should be chosen when taking a picture? It depends on what you want to do with the picture. Do you want to e-mail it to friends, post it on a Web site, make it your computer's wallpaper, print it as a 4" x 6" photograph, or create a poster-sized print?

For images that will be viewed on a computer monitor (such as those you send by e-mail or post to the Web), a low pixel-count setting is perfectly adequate. Since most people view images on monitors that display only 800 x 600 pixels, a low pixel-count image, such as a 600 x 400 photograph, will fill up most of their screen without running off the edges. A low pixel-count setting will also reduce the file size of the image and reduce time it takes others to download or display your image.

Images that you intend to print should be captured at a higher pixel-count setting.
• For a 2" x 3" print, the image dimensions should be 400 x 600 pixels minimum
• For a 4" x 6" print, the image dimensions should be 800 x 600 pixels minimum
• For a 5" x 7" print, the image dimensions should be 1000 x 1400 pixels minimum
• For an 8" x 10" print, the image dimensions should be 1600 x 2000 pixel minimum

If you don't know what you want to do with your image the moment you take a picture, to be safe, it's a good idea to set your camera to the highest resolution setting. You can always reduce the pixel-count of your image later for e-mailing or web publishing.

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 2048 x 1536, we multiply 2048 times 1536 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 2048 x 1536 image is set to print at 300ppi, the resulting print will be 6.8 x 5.1” (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, 2400 x 3000.

If we wanted to make an 8x10 print from a 35mm slide or negative, 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 2400 x 3000. 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.

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 1024 x 768, we would want to make our image resolution (pixel dimensions) 1024 x 768 for desktop wallpaper or full screen display. For e-mail use, we would want to make them smaller, perhaps 512 x 384.

Copyright 2005
Porter's Camera Store
P.O. Box 628
Cedar Falls, IA 50613-0028