Pixel definition (computing)

The word pixel is a combination of pictures (pics or pix) and element. The pixel is the smallest possible unit with which any digital image is composed on a computer. Its plural is pixels or pixels.

Also called pixel, pel, dot, or dot.

The smallest controllable element on a screen such as an LCD is also called a pixel.

Finally there is a line of smartphones from Google called the Pixel.

What is a pixel then?

So, to clear things up, pixel can be:

– The minimum point or element that makes up a digital image (see: rasterized graphic).

– The smallest point or element that can be controlled on a screen. Each of these points has a physical address in coordinates. LCD screens have a two-dimensional grid.

– In the context of sensors in digital cameras, the term pixel is also used. In any case, this article will not develop this topic. It is preferable to use more technical terms like photosite or sensel.

Each pixel has a specific color that can vary in intensity. Color is usually formed using the combination of three or four components such as red, green, and blue, or cyan, magenta, yellow, and black, etc.

It is important to note that the pixels that make up an image (such as JPG, PNG, or similar) do not necessarily match one-to-one with the corresponding physical pixels on a screen.

Pixel of a digital image

In the box you can see the multiple colored pixels that make up that enlarged region of the photograph. Graphic images are made up of a rectangular array of pixels.

To store the information of an image, each pixel is encoded by a set of bits of a certain length (called color depth). For example, a single pixel can be encoded with a color depth of 8 bits (1 byte), and this allows it to take on up to 256 color variants (2 to the power of 8).

In photographic images, three bytes (24 bits) are usually used to define each color of each pixel, with this 16,777,216 colors can be represented. This type of image is called true color.

For more information read: raster graphic.

Pixel as a unit of measure

Pixels are also used as a unit to measure the resolution of a screen, an image and some devices such as digital cameras (which use megapixels).

As for the images, these can be measured through the width and height in pixels, for example an 800×600 image (800 pixels wide and 600 high), which means that it is made up of 480 thousand pixels (equivalent to 0 pixels). .48 megapixel).

Pixels, depending on the context, can also be used in other measures such as: 2000 pixels per inch (or per centimeter), 500 pixels per line or spaced 10 pixels apart.

Dots per inch (dpi) and pixels per inch (ppi) are often used synonymously, but they actually mean different things, especially when used in printing. The dpi is used to measure the density of dots with which the printer prints an image. For example, a high quality 600 ppi image can be printed on a 1200 dpi inkjet printer.

Read: Image Resolution

Read: Screen Resolution

Pixels in LCD screens

LCD displays generally use a stepped grid, where the red, green, and blue components are displayed in slightly different locations.

Technology called sub-pixel rendering takes advantage of this small difference to improve how text is viewed on LCD screens. The image below shows this technique.

The pixels in an LCD are made up of separate red, green, and blue elements, which can be used for finer control over the curvatures of text displayed on the screen. In this case the word will appear white on a screen because the red, green and blue sub-pixels are so small that the human eye cannot distinguish them and they form white light.

See also: Dead pixel.

color depth

The number of different colors that can be represented in a pixel depends on the number of bits per pixel (bbp). An image with 1 bpp uses 1 bit per pixel, so it can only be on or off (two states). Each additional bit doubles the number of colors available, so a 2 bpp image allows 4 colors in each pixel, a 3 bpp image allows 8 colors, so:

1 bpp, 2^1 = 2 colors (monochrome)
2 bpi, 2^2 = 4 colors
3 bpi, 2^3 = 8 colors

8 bpi, 2^8 = 256 colors
16 bpp, 2^16 = 65,536 colors («Highcolor» )
24 bpp, 2^24 = 16,777,216 colors («Truecolor»)

For more information read: Color Depth


Basically, a megapixel is equal to 1 million pixels. Sometimes it is abbreviated mpixel or MP, it is also used as megapixel.

The megapixel is often used to count the number of pixels in a digital image or also to measure the resolution of digital cameras.

To read about this go to: Megapixel.

Origin and history of the name pixel

The word «pixel» was first published in 1965 by Frederic C. Billingsley of JPL (NASA’s Jet Propulsion Laboratory), to describe the elements of video images from Mars and Moon space probes.

Frederic Billingsley said he learned the word from Keith E. McFarland, who worked at the Link Division of General Precision in Palo Alto, California. The latter couldn’t say where he got it from, he simply said «it was used at that time» (around 1963).

As explained at the beginning of the article, the word pixel derives from pix (from picture = image) and element (element). In Spanish, pixel and pixel are used, depending on where the accent is placed. And its plural is pixels or pixels (NOT pixels or pixels).

The concept of «picture element» dates back to the very beginning of television. It is even found on patents for inventions in the US from 1911.

There is also the pel (picture cell) variant that began to be used in 1972.

Pixels or resolution of a photo and printing in centimeters

There is no direct equivalence between the pixels of a digital image and the corresponding centimeters of print. A very small image may print very large on paper, but the pixels in the printed image will begin to show through to the naked eye. There are techniques to «enlarge» the digital image and soften the pixels a bit, but they don’t work wonders.

Yes some calculations can be done so that we can achieve an acceptable print quality of the image. In this way we will be able to know how big we could print a digital image before the pixels are excessively noticeable.

To make this calculation you must know the DPI (dots per inch) that the printer allows printing.

From 200 dpi we can say that the printing resolution is good, and if we want to be sure we must reach 300 dpi or more.

To find out what is the maximum print resolution that a digital image allows (for an acceptable print quality) you have to divide the width of that image by the dpi:

For example, we have an image that is 1600 pixels wide and the print resolution is 200 dpi, 1600/200 gives us 8 inches, that is, about 20.32 centimeters wide we will achieve with acceptable quality.

If printing is done at 300 dpi then: 1600/300 = 5.33 inches is approx. 13.54 centimeters.

Photoshop allows you to do these conversions automatically. I suggest reading this tutorial: Preparing High Resolution Images for Printing

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