What does ‘pixel’ mean?

Com­mu­nic­a­tions would be nothing without images – almost nothing. Even before negative film and prints were replaced by elec­tron­ic recording tech­niques in pho­to­graphy, various data formats for image files had been developed. Popular keywords include RAW, BMP, and TIFF. De­velopers quickly noticed that these formats produced con­sid­er­able file sizes, which were a hindrance es­pe­cially for fast web ap­plic­a­tions. This, in turn, led to the search for pos­sib­il­it­ies in image com­pres­sion. The ‘battle’ between JPG and PNG is far from over, and already new formats are popping up on the horizon – for example, WebP, Google’s in-house image format.

But there’s one thing that all these clever technical formats need to tackle: they must be dis­play­able on an output medium, starting with a more or less large screen with a certain res­ol­u­tion. This is where the term ‘picture cell’ comes into play – a made-up word that was merged into pixel and was first used as a term around 1965. In our guide, you’ll find out what makes up a pixel and what its role is in image rep­res­ent­a­tion.

In the figure above, the raster dots were rep­res­en­ted by the program used (Photoshop). Each pixel has a different colour or hue, which, when put together, create the composite image. To reproduce such an image in HD quality, 1920 x 1080 pixels are needed, which is a total of 2,073.600 pixels. These pixels must be addressed in­di­vidu­ally, in the correct sequence and re­pe­ti­tion rate by the tech­no­logy within the monitor, for example, to make sure that the full image is visible without flick­er­ing and in the correct colour.

The bee image and its cropping have already il­lus­trated how the size of pixels affects optical per­cep­tion. In the early days of the PC, monitors were still devices with classic picture tubes and res­ol­u­tions of 640 x 480 (VGA), then 800 x 600 (SVGA) followed. Not so long ago, the so-called ‘HD-ready’ PC with 1280 x 720 pixels had its time. True HD offers 1920 x 1080 pixels, and the latest 8K full-format systems feature 8192 x 4320 pixels. But the com­pet­i­tion for the number of pixels truly took off with the de­vel­op­ment of LED monitors. They enabled very high pixel densities in a very short time. This tech­no­logy is now part of modern smart­phone displays.

As a measure of the res­ol­u­tion of images for display on monitors, 72 dpi (dots per inch) has proven to be a suf­fi­cient value for the human eye. The smaller these pixels are, the more can be ac­com­mod­ated on a monitor surface, in­creas­ing the overall res­ol­u­tion of the devices. For pro­fes­sion­ally printed materials, 300 dpi is the most common value used.

Once a digital raster image has been created, for example from a digital camera, it can be enlarged sig­ni­fic­antly, but this always reduces the rendering quality. That’s why when faces become un­re­cog­nis­able in photos or videos, the resulting image is often referred to as ‘pixelated’.

The word ‘megapixel’ describes a large number of pixels, one million pixels to be exact. The term emerged when digital cameras and smart­phones with cameras were first ad­vert­ised. It describes the image res­ol­u­tion. However, high-quality cameras can still get a lot out of a subject even if the mega­pixels are not quite as high. With these mega­pixels, high-per­form­ance camera software takes care of sharpness and bright­ness ad­just­ments as well as the sup­pres­sion of image noise, which often plays a greater role in image present­a­tion than a high res­ol­u­tion in mega­pixels alone.