Let’s start with the definition of one pixel is the smallest picture unit in a computer image or display. Now you noticed that every camera specification refers to the number of megapixels that the camera posses - this means million of pixels. All these million of pixels are arranged in a grid. This grid has rows and columns - maybe now the image size makes more sens: 800×600, 1600×1200, 2400×1800, and so on. The camera’s resolution is calculated by multiplying the number of pixels along the length and width of the sensor, however, you must understand that only the effective megapixels matter when working with the pictures.
Each pixel contains data of only one color which is why a bigger number of pixels on a given area will result in more data, more color variations on the same area. As a result, an image with lots of pixels is often called a “high resolution” image with better quality. If the image size is 1600×1200, for example (by the way, this is the postcard standard), and the dpi 72 (dots per inch), the image quality will be lower than the same size at 200 dpi. Some cameras offer the option to shoot jpeg at standard quality (the 72 dpi), and fine quality (180 dpi). The 180 dpi image will require more space on your memory card, but it’s worth. Don’t forget that you can always reduce your image later, but enlarging a picture will only decrease the image quality.
Printers (and scanners - the other way around) also use the therm of resolution and it comes easy to understand that a high resolution image will give a high resolution print, but, things are not that simple. A given resolution can be OK on a monitor, for web publishing (72 dpi), but for paper not (at least 300 dpi). If you choose to print a small image at a large size, the pixels in your image are stretched to fill the requested print area and your eye perceives this as a “pixelated” effect. Below you have some guiding lines in case you want to print your photos:
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 pixels minimum
For stock photography, 1600×1200 is the minimum accepted.
Tags: pixel, megapixels, image size, resolution, dpi, pixels, image quality, compression
