What is Anti-Aliasing? Techniques, Purpose, Types & More

What is Anti-Aliasing?

Anti-aliasing, sometimes referred to as AA, is the term signifying a software process to smoothen the edges of fonts or graphics objects to make them look round.

In other words, anti-aliasing refers to the process of removing the aliasing or the ambient occlusion effects from the 2D objects used in computer graphics. It helps in removing the jaggies.

KEY TAKEAWAYS

• The anti-aliasing technique helps in producing images with perfectly round edges.
• The process adds a discoloration to the edges or lines of the object to make them look smooth.
• In this process extra pixels are added in between the background and the edges of the polygonal objects to make them round.
• Based on the application, there are different techniques for anti-aliasing implemented, and each has different results.
• This technique is usually executed by computer games and graphics cards, but may also be applied in digital photography and even in digital audio.

Understanding Anti-Aliasing

Usually, images are produced by pixels, which are themselves rectangular in shape. This means that the edges of the round object look jagged.

The process of anti-aliasing typically helps in smoothing these edges to give them the perfect round look.

The jagged edges are the results of aliasing or undersampling. This means that the scan conversion is done by using sampling of low frequency, which results in the notable distortion in the images displayed.

This is where anti-aliasing comes into play. The process adds subtle color changes around the edges of the objects so that the human eyes are tricked when they view these lines. It is thought that the lines are smooth and not jagged.

The changes made in the color of the lines are minute and cannot be detected by the human eyes under normal conditions, or unless the image is magnified significantly.

Therefore, it is easy for these changes to blend easily with the background around the lines or curves. This makes the lines look true and smooth.

What are Anti-Aliasing Techniques in Computer Graphics?

There are typically four techniques of anti-aliasing namely, by post filtering or super sampling, displaying objects at a high resolution, pre-filtering or area sampling, and pixel phasing.

Using high-resolution display:

When objects are displayed at a high resolution, it will increase the sampling rate and reduce the aliasing effects.

This is because the jaggies become very small when an object is displayed at a high resolution, so much so that it cannot be distinguished by the human eye. Therefore, the edges get blurred and appear smooth.

Post Filtering or Super Sampling:

In this method, the sampling resolution is increased by treating the screen as if it is made up of finer grids that are a lot more in number.

This reduces the effective size of the pixels, even though the resolution of the screen is the same.

In this method, the average of the intensities of the subpixels is taken into account to find the average intensity of a pixel. Also, the intensity of each individual pixel is calculated.

Therefore, sampling is typically done at a higher resolution and the image is displayed at a lower resolution or at the screen’s resolution, which is why it is called super sampling.

Usually, this method is carried out after the rasterized image is produced, which is why it is also called the post filtration procedure.

Pre-filtering or Area Sampling:

In this method, the pixel intensities are used, but these are calculated on the basis of the proportion of the areas overlapping each pixel with the objects that are to be displayed.

On the other hand, the color pixels are calculated in the reverse way, that is, on the basis of the overlap between the objects in the scene and the pixel area.

Pixel phasing:

This is a technique where the pixel positions are moved to almost the exact position near the object geometry.

In some cases and systems, the size of each individual pixel can be tuned for allotting intensities.

In addition to the above four techniques, there are also a couple of other methods followed in anti-aliasing, such as:

Compensating for line intensity differences:

This is the process followed when the diagonal line and the horizontal line are plotted on the raster display and the desired number of pixels to display both of these lines is the same.

This holds true even though the diagonal line is 1.414 times bigger than the horizontal line.

This reduces the intensity of the larger line, and to compensate for this reduction, the intensity of pixels is allotted based on the length of the line.

Anti-aliasing area boundaries:

This is the process that involves removing the jaggies from the edges specifically. The process is applied to scan line algorithms for smoothing the area boundaries out.

Also, in this process, the positions of the pixels are adjusted to bring them nearer to the area boundaries, provided repositioning of the pixels is allowed.

This is usually done on the basis of the percentage of the pixel area available within the boundary.

What is the Purpose of Anti-Aliasing?

The main purpose of the anti-aliasing technique is to smoothen the edges of the images on a PC by removing the jaggies. It blends the colors and makes them look less blurred and more natural.

Anti-aliasing today is even more necessary, especially on a larger screen, since both the resolution and GPU configurations have improved.

The anti-aliasing filter checks the under-sampled variables for specific frequencies.

It ensures that the sampling rate is the same as or greater than a signal component, based on the Nyquist theorem. This will eliminate the undesirable visual effects and jaggies.

Ideally, the anti-aliasing technique allows the images to achieve the four desired parameters, such as:

• Steepness in the areas of transition
• Desired amount of ripple or attenuation on the passband
• Diverse frequencies of phase relationship
• Desired filter roll-off

The anti-aliasing filters also play a significant role in producing specific functions such as noise filters and Analog-to-Digital Conversion (ADC).

What are the Different Types of Anti-Aliasing?

There are mainly two types of anti-aliasing methods namely, spatial and post-process anti-aliasing. Under these two broad categories, there are different types of subcategories, such as MSAA, SSAA, FXAA, MLAA, SMAA, TXAA, and DLSS. Each of these types has unique features.

MSAA

Also referred to as Multi-Sample Anti-Aliasing, this type is characterized as follows:

• It is one of the most commonly used techniques.
• It is one of the most reliable techniques.
• It offers a complete balance between visual fidelity and performance.
• It uses more than one sample of two or more, usually 2, 4, and 8, samples of adjacent pixels.
• It uses the Enhanced Quality Anti-Aliasing technique developed by AMD.
• It also uses the Coverage Sampling Anti-Aliasing technique developed by NVIDIA.
• It is a more effective technique.
• It causes less strain on the hardware.

SSAA

Also referred to as Super Sampling Anti-Aliasing, this type is characterized as follows:

• It is the fundamental but a more demanding anti-aliasing technique.
• It initially renders an image at a high resolution.
• It down-samples the image to produce a sharper and clearer image.
• It produces great output.
• It may limit the performance of the GPU.
• It is not suitable for use with weaker or older graphics cards.

FXAA

Also referred to as Fast Approximate Anti-Aliasing and designed by NVIDIA, this type is characterized as follows:

• It is suitable for use on low-end computers.
• It is not demanding on the GPU or the hardware.
• It smoothens a 2D image directly and immediately as it is displayed on the screen.
• It may produce blurred images.

MLAA

Also referred to as Morphological Anti-Aliasing, this type can be characterized as follows:

• It is quite demanding on the hardware.
• It blurs the image heavily to remove the jagged edges.
• It blends the pixels just as it is done in FXAA.

SMAA

Also referred to as Subpixel Methodological Anti-Aliasing, this type is characterized as:

• It has similar properties as the MLAA and FXAA.
• It reduces the blur in the images to a minimum.
• It produces sharper and better images.

TXAA

Also referred to as Temporal Anti-Aliasing, this type created by NVIDIA can be characterized as follows:

• It is a complex technique.
• It is a unique and effective method.
• It smoothens the movements easily.
• It is demanding on the hardware.
• It is not used by many games.

DLSS

Also referred to as Deep Learning Super Sampling and developed by NVIDIA, this type is characterized as follows:

• It is compatible only with Volta and Turing GPUs.
• It is an advanced technique.
• It uses deep learning.
• It creates better images with more details.
• It uses tensor cores to produce clearer images at a higher resolution.

Does Anti-Aliasing Reduce FPS?

Yes, more often than not, anti-aliasing will lower the Frame Per Second or FPS. It will be more prevalent in the low-end systems because it will try to blend the colors in the boundaries to create a smooth illusion.

Typically, this effect will come at the cost of the computing power because further calculations will be added to each of the frames.

This will have significant effects on the workloads of two major components of the computer, increasing their jobs, namely:

• The Central Processing Unit (CPU)
• The Graphics Processing Unit (GPU)

This combined effect will reduce the FPS.

However, how much effect anti-aliasing would have on the FPS would typically depend on a few specific factors, such as:

• The type of the game
• The age of the GPU

The drop may be of only a few frames at times, but often it is by a large amount.

However, the more developed and modern Deep Learning Super Sampling (DLSS) technique tries to reduce the effects of anti-aliasing on the FPS and the performance.

Ideally, in this new image rendering technology created by NVIDIA, deep learning technique is used to generate an image that appears to be in a much higher resolution version of the original image which was in a lower resolution.

Also, the magnitude of the effect on the FPS will depend on the type of anti-aliasing technique used. For example:

• FXAA will have an impact of almost 5% to 10%.
• SSAA or MSAA will have an impact of almost 50%.

The SMAA technique, on the other hand, will have an impact of magnitude somewhere in the middle of the two above techniques. It will blur the edges, but not the image.

And, if you consider TXAA, it will blur the image too much but will remove the shimmering effect.

This is because it is a Temporal Algorithm. In this case, the impact on the performance and FPS is comparatively high but is much lower in comparison to the effect caused by MSAA.

No matter which technique is followed, the gist of the matter is that anti-aliasing will enhance the graphics quality with less jagged and smoother edges, but at the cost of the FPS.

Anti-Aliasing Vs Aliasing

• The primary objective of anti-aliasing is to do away with the effects of aliasing, which include jagged profiles, disintegrating textures, and loss of details.
• While anti-aliasing involves averaging the pixel colors at the edges, aliasing involves the visual stair-stepping of the boundaries of the images at very low resolution.

Questions & Answers:

Conclusion

So, now you know that anti-aliasing is a technique that helps to abate visual defects in high-resolution images displayed on a low-resolution system.

You now also know its different types, purposes, importance, benefits, and utility, in spite of being a relatively old concept of smoothing images with round edges.