Counting Pixels

Smaller is not always better, especially when you are dealing with pixels.

Varying in size from one manufacturer to another and even from one camera to another, pixels are the little critters found on your imaging sensor, which are the components that record light on most digital cameras. It therefore makes sense that a larger pixel can record more light if they are larger.

Two sensors with the same number of pixels would be compared as follows: The one with the larger pixels would take a higher quality image than the sensor with the smaller pixels. Scientists have gone crazy reducing things to digital size; a smaller sensor with the same number of pixels would, of course, require smaller pixels.

The smaller sensor may be more efficient because of its size, but it won't usually produce the same quality images as the larger sensor with larger pixels will. Miniaturization isn't always the better way to go.

Digital single lens reflex cameras (SLRs) have a better quality of image than compact or point-and-shoot cameras because they have an imaging sensor close to the size of those found on a 35mm film camera. Even the high-end compact cameras costing up to $1,000.00 use a sensor about 1/1.8" or 5.5mm x 4.1mm. Even with a 3-, 4-, or even 5-megapixel sensor, they can't create photos comparable to the 3-megapixel SLR.

Because the technology is relatively new, many customers are confused by pixel numbers, and manufacturers aren't completely upfront when the talk about pixels either. A camera with 4.3 million pixels may only use 4 megapixels to actually record light information for the image. These are described as the "effective" pixels, and you have to look really hard to find where the manufacturer discusses these in your manual.

However, this is the number you want to use when deciding on the camera's pixel size. If a camera has 3.1 effective megapixels, yet is advertised as a 3.3-megapixel camera, it is still only a 3.1-megapixel camera.

The law requires that the effective pixel count be advertised along with the pixel count, but this isn't always true, so look for it in your cameras manual.

Determining Lines, Inches, and Pixels

If we are aware of the size, density, and number of pixels on a sensor and recognize the other variables to a camera's resolution, are we better able to determine the quality of the images a camera can produce? The answer is a resounding no. Pixels are the units of measurement relating to the camera's resolution only, not the image resolution.

Raw camera resolution is shown in pixels, but image resolution is referred to in ppi, or pixels per inch; that is the number of pixels for every square inch of the photo. A 300 ppi image means there are 300 pixels on each square inch of the image.

Because sensors that are the same size can have a different number of pixels, measuring on the ppi scale is unrealistic. An 8" x 10" photo with a 300 ppi actually has more pixels than a 4" x 6" 300 ppi picture.

Another problem arises when you consider that printers are measured in dots per inch or dpi. Printers use dots of ink to print, not pixels, and different printers use different numbers of dots for each pixel in a picture. The higher the dpi, the higher the quality of the print will be.

Pixels are made of various colors, contrasts, and brightness values; therefore, the more dots of varying colors and quantities, the better the image will be.

Quality photographic prints will require a printer that can print a resolution between 240 and 360 ppi, since this is the resolution required to produce a photo-quality image at a normal viewing distance. What this tells us is that we need to be aware of not only the ppi of the camera, but also the dpi of our printer in order to come up with photographic quality prints.