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.

What is a pixel?

The pixel – or px for short – is the smallest element in a digitally-displayed image. Multiple pixels are usually aligned in a raster on a monitor or a mobile phone display. The com­bi­na­tion of many pixels makes up a raster image.

Close

The eye can easily “decipher” the composite raster graphic. It becomes more difficult, though, or even im­pos­si­ble, when the image in the white frame is enlarged. The eye can easily “decipher” the composite raster graphic. It becomes more difficult, though, or even im­pos­si­ble, when the image in the white frame is enlarged.

Close

In the figure above, the raster dots were rep­re­sent­ed by the program used (Photoshop). Each pixel has a different color 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 color.

What are pixels made up of?

In order for a pixel to represent a specific color, it is composed of subpixels in the colors red, green, and blue (RGB). These subpixels can have different shapes to create a layout with good image de­f­i­n­i­tion and few spaces between the pixel elements. A look at the display of an iPhone 11 Pro, for example, tells you what is tech­ni­cal­ly possible. It has a display size of 2436 x 1125 pixels with a res­o­lu­tion of 458 ppi (pixels per inch). This results in a pixel size of 0.05 mil­lime­ters with subpixels of 0.018 mil­lime­ters (rounded values).

Close

The output color of the in­di­vid­ual pixel is a com­bi­na­tion of the color values of three subpixels in each case. The three colors are mixed ad­di­tive­ly and can, in this way, assume different values. Additive mixing means su­per­im­pos­ing.

Close

If all three primary colors have the maximum value of 255, the output is black. If RGB = 0/0/0, white appears. The values in between allow around 16.7 million shades of color (2563) to be displayed.

Close

Pixel size and image quality

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 un­rec­og­niz­able in photos or videos, the resulting image is often referred to as “pixelated”.

What are megapix­els?

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.