In image quality evaluation (e.g., for cameras, display devices, LiDAR, etc.), test charts are standardized and reproducible core tools—they translate “subjective visual perception” into “objective data metrics.” This article starts from basic concepts, breaking down the purposes, parameters, and selection logic of test charts, as well as chart materials, mounting, usage, and storage, to help you precisely match testing requirements and use test charts correctly.

I. What is a Test Chart? — The “Standardized Ruler” for Image Testing

Test charts are standardized media used to quantitatively evaluate image quality. They contain specific patterns, color patches, gray patches, and other information. By capturing the test chart with the Device Under Test (DUT), core metrics such as resolution, distortion, color reproduction, and noise can be quantitatively evaluated.
In industrial applications, the importance of image test charts is self-evident. They are not only key tools for product quality control but also important references for optimizing imaging system performance during the R&D phase. According to testing standards in different industries, such as QC/T 1128 for the automotive industry, GA/T1127 for the security industry, YY 0068.1 for the medical industry, and Q/CR 967-2023 for the railway industry, specific test charts are required for image quality testing to ensure products meet industry standard requirements.

II. Core Purposes and Classification of Test Charts

(I) Classification by Core Purpose

Test Objective	Corresponding Chart Type	Purpose	Typical Examples
Resolution		Used to evaluate the detail reproduction capability of the imaging system; Common quantitative metrics: MTF50, MTF50P, MTF30, MTF10, Aliasing Onset, etc.	ISO 12233 Resolution Chart Used for DUT resolution testing, visual resolution in different directions can be analyzed through wedge patterns. The corresponding size and line pairs of the chart must be selected based on the DUT's resolution, field of view, and shooting distance. SFR Slanted Edge Chart Complies with the ISO12233:2017 standard, containing 9 low-contrast slanted edge structures at a 5-degree angle, used for DUT resolution testing.
Color		Used to evaluate the color accuracy and white balance performance of the imaging system; Common quantitative metrics: Saturation, color difference, hue angle, etc.	Standard 24-Color Chart 24 scientifically formulated color patches, providing true and natural color reproduction.
Uniformity		Used to evaluate the luminance uniformity, color uniformity, white balance, dead pixels, etc., of the imaging system; Common quantitative metrics: Ratio of center luminance to corner luminance, R/G/B color channel ratios, etc.	18% Neutral Gray Chart A neutral gray chart with 18% reflectance, providing a reliable neutral gray reference to ensure accurate white balance settings in various lighting environments. 70% Light Gray Test Chart The chart surface has a reflectance of 70%, suitable for CMS luminance uniformity (i.e., lateral uniformity) testing.
OECF		Used to evaluate the grayscale / dynamic range / signal-to-noise ratio of the imaging system; Common quantitative metrics: Grayscale resolution levels, dynamic range (DR), signal-to-noise ratio (SNR), etc.	Transmissive 36-Step High Dynamic Range Chart Grayscale distribution meets ISO14524 and ISO15739 standards, with a polarizer added in the center (adjustable light intake), contrast up to 30,000,000:1 (approx. 150dB), supporting extremely high dynamic range testing.
Distortion		Used to evaluate the lateral chromatic aberration, SMIA TV distortion, and FOV of the imaging system; Common quantitative metrics: Distortion SMIA (%), LCA (lateral chromatic aberration), etc.	Reflective Checkerboard Chart Regular square grid arrangement, enabling intuitive measurement of geometric distortions such as barrel distortion and pincushion distortion.
Glare		Used to evaluate the glare condition of the imaging system; Common quantitative metrics: Flare index F, glare ratio, average glare attenuation, worst glare attenuation, etc.	Transmissive Flare Test Chart Complies with the ISO 18844 standard, featuring 17 black test spots distributed on a white background (arranged along double diagonals), specifically for quantifying lens stray light performance.
Others

(II) Classification by Media Type

Reflective Charts
Principle: Relies on external light source illumination; the chart reflects light for imaging;

Transmissive Charts
Principle: The chart itself is a backlit medium, with light transmitting through the back of the chart;

III. Analysis of Key Chart Parameters
(1) Aspect Ratio
Corresponds to the output aspect ratio of the imaging DUT (e.g., camera/display aspect ratio). Common ratios include “4:3” (traditional industrial cameras), “3:2” (DSLR cameras), and “16:9” (automotive/consumer electronics).
→ Selection Principle: The chart aspect ratio must match the DUT imaging aspect ratio to avoid black borders, stretching, or cropping during imaging, which would result in an incomplete test area.

(2) Magnification and Size
Chart magnification (often denoted as X, e.g., 0.5X, 1X, 2X, 4X, 8X) is the scaling factor of the actual effective image size of a reflective test chart relative to the manufacturer's defined base size, used to characterize the chart's “field of view coverage capability.”
→ Selection Principle: When selecting magnification, primarily consider the test distance and the DUT's field of view (FOV). The goal is to have the chart's effective test area occupy 60% - 90% of the camera frame height, providing a sufficiently large and clear image area for analysis software.

• Small magnification (0.1X, 0.2X): Small chart size, suitable for short test distances and small fields of view (e.g., macro testing);
• Medium magnification (0.5X, 1X): Standard size, suitable for medium test distances and regular fields of view (e.g., consumer electronics cameras);
• Large magnification (2X, 5X, 8X): Large chart size, suitable for long test distances and large fields of view (e.g., automotive surround-view cameras).

Given the test distance (S) and field of view (FOV), the chart size can be calculated using trigonometric functions:
Based on the tangent function relationship: $tan\frac{DFOV}{2}=\frac{D /2}{S}$, we can derive: $D=2S\frac{DFOV}{2}$
Similarly: the width and height of the chart can be calculated based on HFOV and VFOV.
When the test object distance is too far and a teleconverter is needed to reduce the distance for shooting, the equivalent field of view must be calculated based on the teleconverter magnification, and then converted to the chart size.

(3) Measurement Accuracy
The “K” in the ISO 12233 resolution chart is a common industry classification (2K/4K/8K, etc.), directly representing the maximum theoretical resolution that the chart can measure.
→ Selection Principle: The maximum theoretical resolution of the chart ≥ the theoretical limit resolution of the device, ensuring that the true performance upper limit of the device can be measured.

(4) Reflectance, Transmittance, and Contrast
Reflectance (R): The ratio of reflected luminous flux to incident luminous flux for reflective charts (%).
Transmittance (T): The ratio of transmitted luminous flux to incident luminous flux for transmissive charts (%).
Contrast Ratio: The ratio of luminance between the brightest and darkest areas on the chart.
Reflective Contrast = Brightest Area Reflectance (R_max) / Darkest Area Reflectance (R_min)
Transmissive Contrast = Brightest Area Transmittance (T_max) / Darkest Area Transmittance (T_min)

→ Selection Principle: Select the corresponding contrast based on testing requirements. For example: resolution testing recommends a low contrast of 4:1 according to the latest ISO 12233 standard; dynamic range testing requires high contrast test charts (e.g., the 36-step transmissive chart has a contrast of approximately 30,000,000:1).

(5) Optical Density (OD)
When testing items such as dynamic range, signal-to-noise ratio, and grayscale levels, a density file often needs to be loaded during image quality analysis. The values in the density file are the standardized optical density values of different grayscale patches. The essence of this value is the logarithmic value of the “degree of light transmission/reflection attenuation,” and the attenuation of the chart's grayscale patches is mainly determined by the material's ability to absorb light.
The calculation formula for OD is as follows:
$OD = \log_{10}\left( \frac{I_{0}}{I} \right)$
Where I_{0} is the intensity of incident light; I is the intensity of transmitted or reflected light. A higher density value indicates that the material absorbs more light (i.e., reflects/transmits less light); a lower density value indicates that the material absorbs less light (i.e., reflects/transmits more light).

(6) Print Accuracy: The Source of Pattern Fineness
Print accuracy is the ultimate “physical fineness” that the chart pattern can achieve. The print accuracy of a chart varies depending on the manufacturing process and material. Insufficient print accuracy will lead to inaccurate line widths, spacing, and shapes of the chart pattern, causing distortion in test data and triggering mass production risks or R&D misjudgments (e.g., if print accuracy is poor, the precise black-and-white line edges required for MTF testing will become blurred or bleed, leading to falsely high/low MTF values; the grayscale patch edges required for dynamic range testing will bleed with coarse density transitions, resulting in large deviations or worthless test data). Conversely, excessively high accuracy requirements will significantly increase costs and deviate from actual needs.

Core metrics:
- Minimum Line Width (μm): The most core metric, referring to the thinnest black-and-white line width that can be stably printed on the chart (e.g., 20μm, 5μm), directly determining the highest test accuracy the chart can accommodate;
- DPI (Dots Per Inch): The basic parameter of the printing equipment, representing the number of printable pixels per inch. It is a reference for calculating the theoretical minimum line width, not the actual accuracy.
Theoretically, DPI and minimum line width can be derived through unit conversion, with the core formula being: $实际最小物理精度（微米）=\frac{25400}{DPI}$
This formula is only a “theoretical value,” and the actual minimum line width needs to be corrected based on the material.

→ Selection Principle: Clarify the accuracy requirements of the test objectives (allowable error, minimum line width, etc.), and then match the corresponding DPI, process, and carrier material.

Comprehensive Selection Guide: (1) Clarify DUT application requirements, (2) Match chart type and aspect ratio, (3) Calculate chart magnification to select the corresponding chart size, (4) Adapt material and contrast according to the test environment and DUT application. Avoid blindly choosing “large size/high parameters”—the right chart ensures test accuracy while controlling costs.

IV. Chart Materials and Mounting Methods

(1) Chart Materials
Print accuracy is the “printing stage upper limit” of chart accuracy, but the material determines whether this upper limit can be realized. The selection of chart material generally directly locks in the material's accuracy upper limit.
Common chart materials are as follows:
Material selection depends on requirements: Ceramic and soda-lime glass are the ultimate choices for ultra-high precision and long-term stable calibration; white PE and PET films are practical solutions balancing cost and performance; photographic film and matte paper are suitable for limited budgets with lower requirements for accuracy and durability.

(2) Mounting Methods
Mounting, simply put, is “fixing + protecting” the chart. It usually involves fixing or laminating the chart onto a certain material or structure to keep the chart flat, durable, and accurate for testing.

V. Usage and Storage of Test Charts
Scientific storage and maintenance can extend the service life of the chart and ensure the stability of its test accuracy.
(1) Scientific Storage and Standardized Operation
1. Temperature and humidity control: Store at a temperature of around 20℃ and a relative humidity of around 40%-60%. Keep away from humid and high-temperature environments to prevent oxidation of the chart coating and mold growth on the substrate. The chart usage environment must be kept clean and tidy, avoiding direct sunlight. It is recommended to use it in a laboratory under standard light sources.
2. Storage method: Hard charts (PVC, glass, etc.) should be individually wrapped in anti-static protective film to avoid scratches and deformation caused by stacking and compression. Flexible film charts should be rolled flat in dedicated cylindrical tubes; folding is strictly prohibited. Glass charts should avoid contact with hard objects to prevent breakage.
3. Standardized operation: Before handling the chart, clean and dry your hands. Avoid sweat or moisture on your hands; wearing gloves and a mask is recommended. Do not use any liquids to clean the chart; it is recommended to use compressed air to clean dust off the surface.

(2) Chart Maintenance and Scrapping Standards
Chart Maintenance: High temperatures, humidity, ultraviolet rays, and dust can cause chart mold, edge curling, delamination, and fading. Improper cleaning will wear the coating. Fingerprints and scratches will affect the accuracy of test results. Therefore, charts need regular calibration to assess wear. Generally, colorimetric and densitometric equipment is used to check the chart's condition, evaluating whether maintenance or replacement is needed through quantitative data (e.g., color deviation, spectral reflectance).
Scrapping Standards: Black-and-white charts are generally recommended to be replaced every 2 years; color charts are generally recommended to be replaced every 1 year. Immediate replacement is required if there is damage, scratching, dirt, missing parts, or creases in the pattern area.