Recognizing Artifacts

Not a Filtering Guide

This page focuses on identifying artifacts rather than providing detailed filtering solutions. For specific filtering techniques, refer to the relevant pages in the filtering section of this guide, which will be linked throughout where applicable.

As a video encoder, you will inevitably encounter artifacts in your video. These are flaws in the source material, and your job is to fix them if possible, or at least to make them less noticeable. No video is perfect, but with a little bit of finesse, a lot of problems can be suppressed or even entirely eliminated.

Types of Artifacts

Most artifacts can be broadly categorized into two distinct yet closely related types:

1. Mastering defects
2. Authoring defects

Defect Categories Are Not Absolute

While certain artifacts tend to appear more frequently during specific stages of production, any type of defect can potentially occur at any point in the process.

For example, poor deinterlacing is commonly associated with authoring, but a studio might also apply it during mastering or send deinterlaced masters to a distributor. Similarly, compression artifacts typically arise during authoring, but can also be present in the master if it was poorly archived or transmitted.

Be flexible in your understanding of where an artifact may have originated from, as the same visual artifact may require different solutions depending on its origin!

Mastering defects

Mastering defects are imperfections inherent to the master of video content. These typically arise from technical limitations in the production studio's software and equipment during the anime production and mastering process. While many mastering defects are inherent to the original production, some may be introduced later through subpar remastering efforts.

Common mastering defects include:

• Low-quality upscales
• Aliasing in computer-generated 3D content
• Excessive artificial sharpening
• Visible banding in gradients due to limited bit depth
• Orphan fields introduced in telecined content

Authoring defects

Authoring defects are flaws introduced into the source material during the authoring process, such as Blu-ray/DVD authoring, poor analog-to-digital transfers, or compression for streaming platforms. These artifacts commonly originate from the encoding process and various authoring tools used by distribution companies and streaming services. As a result, these defects may appear on some releases but not others, even for the same shows.

Common authoring defects include:

• Heavy quantization (a.k.a. compression) artifacts
• Improper colorspace conversion
• Lowpass filtering
• Poor deinterlacing or IVTC

Trade-offs

A common misconception among both new encoders and those unfamiliar with encoding is that every single artifact must be fixed. This is far from the case. Each filter applied to a video comes with its own costs and trade-offs, and it's crucial to understand when leaving an artifact unfixed may be preferable to introducing new problems through aggressive filtering. Nearly every single filter has the potential to degrade video quality in some way.

There are some exceptions to this general rule, particularly with filters that perform the mathematical inverse of a known operation. A prime example is descaling, which reverses the upscaling process to remove artifacts introduced during upscaling, while allowing you to re-upscale the image using a much better algorithm. However, even these "inverse" filters will cause issues if misapplied, and come with their own limitations and requirements.

When deciding whether to apply filtering, you should carefully weigh the benefits against any potential drawbacks. If you're confident the pros outweigh the cons, then proceed with the filter. But if you're uncertain about potential side effects, it's often better to either skip the filter entirely or thoroughly compare the results to ensure the trade-offs are worthwhile.

Frame Composition

Before you can effectively identify and address artifacts, it's essential to understand the fundamental components that make up a frame. Different regions within a frame have distinct characteristics that make them more or less susceptible to specific types of artifacts.

The following sections break down the key regions you'll encounter and how they interact with various artifacts. By learning to recognize these distinct areas, you'll be better equipped to:

1. Identify where artifacts are most likely to appear
2. Understand why certain artifacts occur in specific regions
3. Make informed decisions about trade-offs in your filtering choices

Different types of regions of a frame

It's recommended you open this image in a new tab and zoom in on it to get a better look at the different regions.

Flat Areas

Flat areas are regions in a frame characterized by low-frequency components and minimal pixel-to-pixel variations. These areas tend to have very subtle color and brightness transitions, if any at all.

Due to their uniform nature, flat areas are particularly susceptible to artifacts like banding, blocking, and quantization noise.

Common examples include:

• Solid colored backgrounds (e.g., title cards, UI elements)
• Clear, cloudless skies
• Smooth surfaces like walls, skin, or polished materials
• Uniform gradients (e.g., lighting transitions, shadows)
• Out-of-focus backgrounds (bokeh)

Hard Edges

Hard edges encompass any sharp, clearly defined transitions between different regions in an image. These edges provide high contrast between objects and their surroundings.

Hard edges are high-frequency information, and are therefore particularly susceptible to compression artifacting, as well as artifacting that results from poor upscaling, such as ringing, aliasing, and blurring.

Common examples include:

• Character line-art
• Text and subtitles
• Sharp boundaries between objects in the background
• Geometric shapes and patterns
• Architectural features like window frames or building edges
• Strong shadow boundaries

Textures

Textures are more complex and can contain a mix of high-frequency and low-frequency information. This makes it difficult to target them specifically without introducing unwanted detail loss.

Textures are often found in:

• Complex patterns like wallpaper or floors
• Natural elements like wood, stone, or fabric
• Detailed backgrounds like foliage or water

Dithering

Dithering is a technique used to help prevent banding and other color break-ups during compression. This is not an artifact in and of itself, but it can be difficult to immediately recognize the difference between dithering and textures, and dithering and compression noise. The big thing that usually sets them apart is the noise structure. Dithering is usually random, while textures are usually structured. Noise can still be somewhat random both spatially and temporally, but usually has a discernible structure.

The colors of noise applied for dithering will impact the noise structure as well as which frequencies they are most visible in. Some colors will be more difficult to get rid of, and may require leaving alone. In almost all cases, you will want to try to match the original noise color when redithering at the end of your filtering script.

Noise Color	Description
White noise	Equal intensity at all frequencies
Blue noise	Concentrates energy in higher frequencies, perceptually uniform
Violet noise	Intensity increases with frequency
Pink noise	Intensity decreases with frequency
Brown noise	Intensity decreases more steeply with frequency

Spatial vs. Temporal

Artifacts can appear either spatially, temporally, or as a combination of both:

• Spatially (static, easily visible in a single frame)
• Temporally (dynamic, visible only in motion)

Spatial artifacts are visible when looking at a single frame, and generally stay static from frame to frame. These include things like:

• Banding in gradients
• Ringing around edges
• Aliasing
• Blurring from poor upscaling

Temporal artifacts only become visible when watching the video in motion. Common examples include:

• Shimmering
• Flickering
• Motion judder
• Interlacing

Temporal artifacts are more difficult to fix and will require motion compensation to some extent, which is also rather expensive in terms of processing power.

Artifacts

Not Exhaustive

This list covers artifacts you are likely to encounter, but is not exhaustive. Many artifacts can manifest in different ways or combine characteristics of multiple categories (for example, poor upscaling can cause blurring, aliasing, and ringing). When diagnosing issues, focus on understanding the underlying causes rather than strict categorization.

Banding

Frame with banding

Exposure

This frame has additional exposure applied to it to help make the banding more visible in the marked region.

Banding is one of the most prevalent artifacts in digital video. It appears as visible "steps" or bands in what should be smooth gradients, such as in skies, shadows, or other areas with color transitions. This artifact occurs when there isn't enough precision to represent subtle color and brightness variations smoothly. There are two main causes:

1. The video was encoded with an insufficient bit depth, meaning there aren't enough distinct values to represent smooth gradients.
2. During production, processing was done at a low bit depth, introducing banding that gets "baked in" to the final output.

Most modern production workflows use 16-bit color precision during editing and VFX work. For final distribution, this is usually reduced to 10-bit, which is generally sufficient for most content. However, most consumer video content is further reduced to 8-bit color, which only allows 256 distinct values per color channel. This significant reduction in color precision often makes banding visible, especially in scenes with subtle gradients and darker areas of the image¹.

Bit Depth	Colors Per Channel
16-bit	65536
10-bit	1024
8-bit	256

The process to fix this is called "debanding". Additional dithering is usually applied after to preserve the gradient during the encoding stage.

Chroma banding

In some cases, banding may be more noticeable in the chroma planes than in the luma plane. This is because the chroma planes are often compressed more heavily than the luma plane.

Frame with chroma banding

Aliasing

Aliasing is a sawtooth-like artifact that occurs on hard edges. It is caused by a lack of high-frequency information, and is often a sign of poor upscaling or a lack of proper line smoothing.

There are four common causes of aliasing:

1. Poor upscaling algorithms
2. Poor (3D) rendering
3. Binarized line art that wasn't smoothed
4. Stylistic choices

Poor upscaling algorithms

Poor upscaling algorithms are the most common source of aliasing artifacts. When an image is upscaled, the algorithm must create new pixels to fill in the gaps. Most basic algorithms struggle to handle sharp transitions smoothly, resulting in jagged edges and stair-stepping patterns.

Frame with aliasing

Poor (3D) rendering

Poor rendering can cause aliasing in the same way that poor upscaling can. 3D rendered content especially is prone to aliasing when the rendering process lacks sufficient anti-aliasing. This is particularly noticeable on high-contrast edges and fine geometric details.

Frame with aliasing

Non-poor 3D rendering is common in western cartoons, resulting in an overall very jagged look.

Frame with aliasing

Binarized line art that wasn't smoothed

During animation production, frames are binarized to create clean, sharp lines for the coloring process. This step is normally followed by line smoothing to prevent aliasing. However, if this smoothing step is skipped, the resulting lines will still be aliased.

Frame with aliasing

Stylistic choices

Modern animation sometimes employs deliberately jagged or pixelated lines as a stylistic element. These artistic choices are usually obvious and should be preserved rather than "fixed" through anti-aliasing.

Frame with intentionally jagged lines

Ringing

Lowpass filters

Noise

DCT noise

Grain

Blocking

Range compression/expansion

Luma overflow/underflow

Interlacing

Combing

Orphan Fields

Shimmering

Cross-conversion

Blending

Dimming

Point-scaled chroma

Chroma shift

Chroma bleed

Rainbowing

Dotcrawl

Double composite

IRE units

Scanning defects

Cel degradation

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1. Tom Scott's Why dark video is a terrible mess goes into more detail on why this happens. ↩