Font Rasterization | API Solution for .NET

What is font rasterization?

Font rasterization is, in simple words, the conversion of vector-based fonts (such as TrueType or OpenType fonts) into a bitmap or raster image. Then the image can be displayed on a screen or printed on paper. So the purpose of font rasterization can be explained by comparison of two types of fonts relying on the graphics they are created with.

Vector-based fonts are defined using mathematical equations and are scalable, so they scale without losing quality. However, raster displays (such as computer screens) and printers require pixel-based images, so vector fonts must be rasterized to be displayed or printed.

The process of font rasterization involves analyzing the vector data and determining the appropriate pixels to use to create a bitmap image to represent the font at a specific size and resolution. Different rasterization techniques can give different levels of quality in the resulting font image.

Why rasterize fonts?

There are a few reasons to convert vector fonts to bitmap ones:

Types of rasterization

There are two main types of rasterization: software rasterization and hardware rasterization.

Software rasterization refers to the process of rasterizing graphics using the CPU (central processing unit) of a computer. It is done by converting vector-based graphics or fonts into bitmap images. This type is often used in software applications where high-quality rendering is necessary. Software rasterization can be slower than hardware rasterization, as it depends on the processing capability of the CPU.

Hardware rasterization needs specialized hardware (such as graphics cards or GPUs) to rasterize graphics to proceed. This type of rasterization is much faster than software rasterization because it offloads much of the processing to the dedicated hardware. It is mostly used in video games and other graphics-intensive applications.

Methods of rasterization

There are two different approaches to creating digital images(or fonts in our case): pixel-based and vector-based methods of rasterization. Let’s compare them in the table.

Images are made up of individual pixels, each with a specific color value.Images are made up of mathematical shapes and lines.
Images are resolution-dependent, - they are made up of a fixed number of pixels and may lose quality if scaled.Images are resolution-independent, - they can be scaled without losing quality.
Pixel-based images are better for complex and detailed images, such as photographs or highly-detailed illustrations.Vector-based images are better for simple and geometric images, such as logos or icons.
Images are created using rasterization, using the conversion of vector-based data into a pixel-based format.Images are already in a mathematical format.
Pixel-based images need more memory and processing power to create and display.Vector-based images require less memory and processing power.

Algorithms of font rasterization

The process of rasterization involves different algorithms that work together to create a high-quality and readable representation of the font. The most used of them are:

These algorithms together create a high-quality representation of the font. They take into account factors like the resolution of the device, the size of the font, and the digitalization and clarity of the result text.

How font rasterization interacts with display technologies?

The way fonts are rasterized impacts differently on how they appear on different display technologies. The most famous of them are CRT, LCD, and OLED screens. Let’s find out how rasterization affects each of these technologies:

CRT (Cathode Ray Tube) screens: These are older display technologies that use an electron beam to display images. When fonts are rasterized for CRT screens, they can appear slightly blurry. That is because of the way the electron beam scans the screen. But as these screens have lower resolutions than modern display technologies, font hinting and rasterization techniques for lower resolutions may be more effective.

OLED (Organic Light Emitting Diode) screens: This is a newer display technology that uses organic compounds to emit light. When fonts are rasterized for such screens, they may seem very sharp and clear because of their high pixel density. The drawback of OLED screens is that they may be more susceptible to burn-in or image retention. This can cause static images, including text, to leave a ghostly image on the screen.

LCD (Liquid Crystal Display) screens: This is the most common modern display technology. When fonts are rasterized for such screens, they may look sharper and more defined than on CRT ones. However, LCD screens have a fixed pixel grid. This means that fonts may appear jagged or pixel-looking if they are not rasterized at the correct resolution.

ClearType technology

ClearType is a font smoothing technology from Microsoft designed to increase the readability of text on LCD displays. The technology uses a subpixel rendering technique that adds additional detail to the edges of characters, making them appear sharper and more distinct.

ClearType analyzes the individual characteristics of LCD displays to find out the optimal settings for font smoothing. These settings are then used to adjust the subpixel rendering of fonts. It helps improve the overall quality and readability of text on the display.

FreeType technology

FreeType is a font rendering engine used to render TrueType, OpenType, and other font formats. It is an open-source software library that provides a platform-independent interface for rendering fonts on various devices and operating systems.

One of the key features of FreeType is its support for subpixel rendering, which uses the color information of individual subpixels on an LCD display to improve the sharpness and clarity of the text. It also supports font features such as ligatures, kerning, and hinting, that improve the quality of text rendering.

FreeType is used in many popular applications and operating systems, including Android, Linux, and Firefox. It is also used in many game engines and other software that requires high-quality font rendering.

Summing up, font rasterization techniques and font hinting are important to render fonts clearly on all types of screens. The optimal techniques vary depending on the display technology used. That is why font designers should experiment with different techniques to find the best results for a specific display.

Font rasterization impact on performance

Font rasterization impacts performance, particularly when rendering text in real-time applications such as video games or web browsers. The table below explains some ways in which the process can be optimized for speed and efficiency:

Optimisation wayDescription and impact
CachingThe technique that stores previously rasterized fonts in memory. Because of that, they can be quickly retrieved and reused. Caching significantly reduces the amount of time required to rasterize fonts and improve overall performance.
Subpixel renderingIt uses the individual subpixels of an LCD screen to improve the sharpness and clarity of the text. This technique can be computationally intensive, but it can be optimized. For this apply subpixel rendering to specific font sizes or use precomputed subpixel rendering tables.
Simplifying outlinesTo simplify font outlines you need to reduce the number of control points or convert curves to straight lines. This makes rasterization faster and decreases the amount of memory required to store font data.
Pre-rasterizationIt rasterizes fonts at specific sizes and stores them in memory. This decreases the computational cost of rasterizing fonts at runtime, but it can also increase memory usage.
Multi-threadingThe way uses multiple processor cores to rasterize fonts simultaneously. This improves performance by parallelizing the process.
Hardware accelerationGraphics hardware such as GPUs is sometimes used to accelerate font rasterization. For this, the computation is offloaded to specialized hardware. Hardware acceleration can significantly improve performance but requires support from the operating system and graphics drivers.

So as we can see, rasterization impacts performance. There are several techniques that can be used to optimize it for speed and efficiency and the optimal ones vary depending on the specific application and the hardware being used.

Potential future developments in font rasterization

While font rasterization progressed significantly over the years, there is still potential for further development here. Let’s point at some potential future developments in this field:

All these potential future developments are aimed to get even more accurate and consistent font rendering and improved legibility and cross-platform clarity of texts.


Raster fonts are fonts created with pixel-based images or bitmaps. Font rasterization is a critical step in the rendering of text on digital devices. It also can significantly impact the readability and clarity of the text. It is worth mentioning that different rasterization techniques can give different levels of quality in the resulting font image.

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