Pictures on screens are made of tiny dots.
These dots are in neat rows. Each dot has its own color. They work together to make a photo. This helps us see pretty things.
Can you see the dots?
Pictures on screens are made of tiny dots.
These dots are in neat rows. Each dot has its own color. They work together to make a photo.
These dots are called pixels. A pixel is a tiny square. When you zoom in, you can see them. They can be red, green, or blue. Many colors mix to make a real picture. This helps us see many details.
It is like a big grid of colored squares.
A raster graphic is a digital image. It is made of a grid of tiny squares. These tiny squares are called pixels.
Each pixel holds one specific color. Most images use the RGB color model. This means pixels use red, green, and blue to make colors.
By mixing these three colors, a computer can make millions of different shades. This makes raster images great for photos. They can show complex details and many colors.
Raster images have a set size. This is called resolution. It is the number of pixels across the width and height. If you try to make a raster image much bigger, it may lose quality. This happens because the squares become easy to see.
Computers use different ways to save these images. Some ways are called compression. This helps make the file size smaller. Some types are lossless. This means the image stays perfect. Other types are lossy. These make the file small by only guessing the colors.
Many printers and screens use the raster way to show pictures.
A raster graphic is a digital image made of a grid. This grid is made of tiny colored squares called pixels.
Each pixel is a single unit of color. Raster images are perfect for photographs because they show complex details. They store the exact color for every single pixel in the grid. This is different from vector graphics, which use math to draw lines. Raster images are defined by their width and height in pixels. This size is often called the resolution.
To make an image, the computer follows a specific way it works. It uses a two-dimensional array to organize the pixels. Most color images use the RGB color model to create shades. This uses red, green, and blue light to make colors. Each color channel often uses 8 bits of data. This allows for over 16 million different colors in one image. When saving a file, the computer uses a row-major format. It lists all the pixels in the first row from left to right. Then, it moves immediately to the second row.
People have used these ideas for a long time. The word "raster" comes from the Latin word "rastrum," which means a rake. This name comes from how old monitors worked. They used an electron beam to scan the screen line by line. In the late 1960s, A. Michael Noll invented an early scanned display. He worked at Bell Labs on this invention. He filed a patent for it in February 1970. Later, in 1977, a legal issue happened at the Supreme Court. This case involved whether computer software could be patented.
There are many ways to handle these large files. High-resolution grids take up a lot of storage space. Because of this, computers use compression to make files smaller. Some methods are called lossless, so the image stays perfect. Others are called lossy, which means the computer makes an estimate. Common file types you see online include JPEG, PNG, and GIF.
Some very large sensors can capture huge amounts of data. The Vera C. Rubin Observatory uses a sensor with 3.2 gigapixels. This single image creates a file that is 6.4 GB in size.
You see raster graphics every single day. Most modern flat-panel LED monitors use this approach. They refresh the screen by scanning through the pixels quickly. Almost all printers, like inkjet and laser printers, use raster grids too. Even medical tools like MRI scanners use a 3D version called voxels. In geography, people use grids to map things like temperature. Each pixel represents a specific spot on the Earth's surface. Whether you are playing a video game or looking at a photo, you are seeing a raster.
A raster graphic is a digital image built from a rectangular grid. This grid is made of tiny colored squares known as pixels, which is short for "picture elements."
Unlike vector graphics that use mathematical formulas to draw shapes, raster images store the specific color of every single pixel. This makes them the best choice for photographs and images with very complex details. They are defined by their dimensions, which are the width and height in pixels. They are also defined by color depth, which is the number of bits used for each pixel.
To create these images, the computer uses a process called tessellation. This means it tiles a flat plane into a two-dimensional array of squares. In digital photography, this plane is the visual field captured by a sensor. In computer art, the plane is a virtual canvas. In geographic information systems, the plane is a projection of the Earth's surface. Each pixel in the grid has a constant size, which is called the resolution or support. The computer stores a single numeric value for each pixel to represent its color or other data.
Most modern color raster formats use the RGB color model to represent color. This model uses three color channels: red, green, and blue. Each channel typically uses 8 bits of data, which provides values from 0 to 255. By combining these channels, a single pixel can represent over 16 million distinct colors. Some specialized sensors can even go beyond this. For example, the Vera C. Rubin Observatory uses a large CCD sensor. It captures 3.2 gigapixels in a single image, which creates a 6.4 GB raw file. This sensor uses over six color channels to exceed the spectral range of human vision.
When a computer saves a raster image, it must serialize the data. This means turning the 2D grid into a long list of numbers. The most common method is called row-major format. In this format, the computer lists the cells in the first row from left to right. It then moves immediately to the second row and repeats the process.
To reconstruct the grid, the file must include a header section. This header contains essential information like the number of columns and the pixel datatype. It may also include metadata tags, such as those found in the Exif standard.
Because high-resolution grids contain so many pixels, they require a lot of storage. To solve this, engineers use compression algorithms to make files smaller. Some algorithms are "lossless," meaning the original pixels can be perfectly regenerated. An example is Run-length encoding (RLE), which looks for repeated values and stores them as a single value plus a count. Other algorithms are "lossy," meaning they only provide an approximation of the original data. JPEG is a common example of a lossy format. Other popular formats used on the web include GIF and PNG.
The history of the word "raster" traces back to the Latin word "rastrum," meaning a rake. This name comes from the way cathode-ray tube (CRT) monitors worked. These old monitors used an electron beam to scan the screen line by line. This process is called a raster scan. In the late 1960s, A. Michael Noll invented an early scanned display at Bell Labs. He filed a patent application for this in February 1970. However, a legal battle over the patentability of software reached the Supreme Court in 1977, and the patent was abandoned.
Today, you can see raster graphics in many different technologies. Modern flat-panel LED monitors use a raster approach to refresh the screen. They scan through pixels and color them according to bits in memory. Almost all modern printers, including inkjet and laser types, create images as a raster grid. In medical imaging, such as MRI scanners, scientists use a three-dimensional version called a voxel. Even geography uses rasters to represent fields like temperature or soil moisture. In these systems, each pixel is called a cell and represents a specific area of the Earth.
Where will your curiosity go next?
🖼️ Images & Media (4)
More to explore
✨ What else?
Related topics you might enjoy
🔬 Go deeper
More advanced topics to explore
🪜 Step back
Simpler topics to build understanding
What is Nepedia?
A free, ad-free encyclopedia for children. Every article is written at five reading levels, so the same page works for a five-year-old and a fifteen-year-old — use the level switcher above to see this one change. No account needed to read.