What is a pixel? How to define ‘pixels’ and ‘megapixels’ in a digital camera image.
What’s all this talk I hear about endangered megapixels?
I start my Introduction to Digital Photography classes and workshops with a version of this brief ‘working’ definition of, “What is a pixel?”
(I use the term ‘working’ in this context to mean a definition that works for many people, helps the visualization of the subject, but may not be scientifically precise enough for other readers.}
The definiton of ‘Pixel’ that I will use here is:
“A pixel is a description of color and brightness.” It is the stuff that digital images are made of. It is the smallest element of a digital image.
When you take a picture with a digital camera, whether professional DSLR, point and shoot, webcam, etc., you get an array of pixels which form, and in fact are, the digital photo image. The pixels, in these current kinds of digital cameras we use and love, are little tiny squares. Each tiny little square represents some detail from your subject. In this example, I have purposely zoomed waaay in to the image to show the individual pixels. Whenever you zoom in this close, the whole of the image recedes as the pixels themselves are revealed. (I explain why I chose this image at the bottom of the post)
So, each detail of your subject, say an eyelash or a tree on a far away mountain, is projected by the camera lens onto the digital camera sensor chip (or film frame) and falls onto an area of the chip. The chip has, on most cameras, several ‘photosites’ which see different color aspects of the ‘eyelash details. The camera’s internal processing software (called firmware) takes the info from a very small group of adjacent photosites and makes one pixel for your photo pleasure. This happens ‘under the hood’ and you aren’t aware of this part of the image making process.
With black and white film we call a similar thig ‘grain’ or ‘film grain’. On color film it’s usually called ‘dye cloud’. Either way it’s the smallest detail in a film image.
What you get is one pixel representing one small area of your subject’s detail. And this one pixel is arrayed with all the other pixels in a rectangular grid of so many pixels wide by so many pixels high. For example only, a camera might make a digital picture 3000 pixels wide by 2400 pixels high. (This might be written as 3000px by 2400px, or 3000 x 2400, or some similar variation.)
If you multiply the width by the height you get the elusive ‘megapixels’. In this example, 3000 times 2400 equals 7,200,000 pixels, or 7 million 200 hundred thousand pixels, or the easy way to say it:
You only get so many pixels from your digital camera picture. It is based on the actual chip hardware in the camera. So many pixels wide by so many pixels high. That’s it and no more. This will eventually equate into how large a print you can make without getting a ‘pixelated’ look to the image. See my post on ‘Resolution’ for more info on this.
I chose this image because it exaggerates the effect of looking closely at the pixels. It is a bit of a slow shutter shot on slightly grainy color film, scanned, and then enlarged well beyond quality, specifically to enhance the pixelated appearance. I know, I know; it’s not a very sharp shot, and, I’m not a great fan of otherwise ‘cute’ pix, but come on now. Doesn’t this make you smile just a teeny bit?