Positive checkerboard
Opaque dark squares on a contrasting light field provide known internal corners for camera calibration. Choose the grid, substrate and illumination as one specification.
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Technical specifications
Select the values for the actual substrate and process. Material properties and coating options do not automatically apply to every board; define acceptance values on the drawing.
Glass target
Photolithographic dark squares on glass or fused silica. Specify whether the light field remains clear for transmission or has a white backing for reflected light.
| Checkerboard geometry | Square pitch, square rows and columns, and internal-corner count to drawing |
|---|---|
| Substrate | Fused silica / soda-lime glass |
| Process | Photolithography |
| Line-width tolerance | ±0.2 µm |
| Minimum feature width | 0.55 µm or 1 µm, by pattern configuration |
| Feature and overall accuracy | ±1 µm |
| Clear-area transmission | >95% at 550 nm |
| Chrome finish | Yellow, low-reflection blue or bright chrome |
| Optical density | Yellow chrome OD 3; blue chrome OD 5 |
| Glass thickness | 1, 1.6, 2.3 or 3 mm (±0.2 mm) |
| Large-format glass thickness | 4.8 mm for the 500 × 500 mm format |
| Outline size | From 2 × 2 mm up to 800 × 960 mm |
| Outline tolerance at maximum format | ±0.1 mm at 800 × 960 mm |
| Fused-silica expansion | <5.0 × 10⁻⁷/K at 20–200°C |
| Low-reflection chrome reflectance | <13.4% at 550 nm; <1.8% at 650 nm; <2.67% at 750 nm |
| Surface flatness | <0.55 µm for lengths <50 mm; <2 µm for lengths <100 mm; <5 µm for lengths >100 mm |
| Chrome coating thickness | 120 ±5 nm (1200 ±50 Å) |
| Surface roughness | <0.025 µm |
| Optional white backing | 40 µm coating; 10 µm minimum feature width |
| Outline shape | Square |
| Positive pattern polarity | Opaque dark squares on a clear or white-backed field |
Ceramic target
Opaque ceramic with contrasting dark and light squares is used with reflected illumination. Matte and polished finishes have different glare behaviour.
| Checkerboard geometry | Square pitch, square rows and columns, and internal-corner count to drawing |
|---|---|
| Substrate | Zirconia or alumina ceramic |
| Process | Photolithography |
| Line-width tolerance | ±0.2 µm |
| Pattern options | Matte chrome on matte ceramic; bright chrome on glossy ceramic |
| Minimum feature width | 4 µm matte; 2 µm glossy |
| Feature accuracy | ±2 µm |
| Outline accuracy | ±0.05 mm |
| Ceramic thickness | 1 mm (±0.1 mm), 2 mm or 3 mm (±0.1 mm) |
| Outline size | From 2 × 2 mm up to 228 × 228 mm |
| Outline size tolerance | ±0.1 mm at minimum and maximum formats |
| Flatness | <30 µm below 100 mm; <60 µm below 200 mm |
| Chrome coating | Matte chrome or bright chrome |
| Chrome thickness | 120 ±5 nm (1200 ±50 Å) |
| Surface roughness | 0.2–0.7 µm |
| Thermal expansion | <6.7 × 10⁻⁶/K at 40–400°C |
| Matte chrome reflectance | <12.88% at 550 nm; <10.62% at 650 nm; <12.23% at 750 nm |
| Bright chrome reflectance | <9.56% at 550 nm; <1.89% at 650 nm; <11.168% at 750 nm |
| Density | ≥3.66 g/cm³ |
| Rockwell hardness | ≥80 HRA |
| Optional protection | Thin protective layer above the chrome pattern |
| Edge and hole options | Laser-cut outline, hole, chamfer or bevel |
| Finish and shape | Matte or glossy; square, elliptical or drawing-defined cutouts |
| Positive pattern polarity | Dark and light reflective squares; no transmitted-light mode |
Photographic film target
Photographic film supports a lightweight dark-square pattern on a clear field. Define its support and environmental conditions for coordinate measurement.
| Checkerboard geometry | Square pitch, square rows and columns, and internal-corner count to drawing |
|---|---|
| Process | Photographic-film lithography |
| Application | Transmitted-light or backlit functional testing |
| Minimum feature width | 10 or 30 µm |
| Feature accuracy | ±10 µm |
| Film thickness | 0.18 mm (±0.01 mm) |
| Temperature-related dimensional change | 10 µm per °C per metre |
| Environmental response | Film dimensions also respond to humidity; control temperature and relative humidity during coordinate measurement |
| Emulsion | Silver halide, approximately 2 µm |
| Clear-area transmission | >90% across 400–700 nm |
| Optical density | OD >4 in solid black; grayscale density can be specified |
| Maximum format | 0.71 × 0.81 m at 10 µm minimum width; 1.68 × 3.5 m at 30 µm |
| Maximum-format tolerance | ±0.1 mm for both maximum formats |
| Pattern and cutting | Black, grayscale or sinusoidal grayscale; straight, laser-cut or perforated outline |
| Positive pattern polarity | Opaque dark squares on a clear film field |
Define the corners your software reads
A checkerboard corner is where four alternating squares meet. C columns by R rows of complete squares provide (C − 1) by (R − 1) internal corners. The physical square pitch sets their coordinate spacing; record row and column order in the same orientation used by the detector.
- Pattern
- Opaque dark squares
- Field
- Clear or white, by configuration
- Coordinate input
- Inner corners and square pitch
- Viewing side
- Defined on the drawing
Choose material with the light path
Glass and fused silica
Transparent substrates can carry photolithographic chrome squares. Define material grade, active-area flatness, coating and whether the light field stays clear or receives a white backing.
Ceramic and film
Ceramic supports a reflective, durable pattern but does not transmit light. Film supports larger lightweight patterns; mounting and temperature or humidity changes can affect coordinate stability.
Larger or permanent installations
Carbon-fibre composite and metal plate may be considered when mass, stiffness or handling matters. Their patterning and flatness requirements must be specified for the actual construction, not borrowed from glass or ceramic tables.
Accuracy starts at the working plane
A planar calibration model uses known corner positions in one plane. Pattern pitch, corner placement and flatness in the installed state all matter. A numerical subpixel corner estimate is not proof that the physical target or completed calibration has subpixel accuracy.
Use enough board positions and tilts to cover the image field. Inspect detected-corner order, glare and focus, then review residuals and an independent measurement before accepting the camera model.
Edge definition
Sharp, consistent light-to-dark transitions help the detector locate corners. Inspect edge defects and local contrast under the actual lighting and exposure.
Reflection control
A matte finish or low-reflection coating can reduce highlights in reflected light. Choose the surface finish for the illumination geometry rather than assuming one finish suits both reflection and transmission.
Where it is used
Camera intrinsics and distortionKnown physical corners captured across the image support estimation of focal parameters, principal point and lens distortion.
Stereo and 3D visionBoth cameras observe the same grid to estimate relative pose. Keep detectable corners inside their overlapping field of view.
Industrial measurementA verified corner grid can establish image geometry for dimensional inspection when the board coordinates and mounting are controlled.
Specify the board on your drawing
Send square pitch, square and internal-corner counts, active area, outline, substrate and thickness, dark-square layout, background finish, pattern side, lighting and the inspection values you need recorded.
Common questions
What makes this a positive checkerboard?
The specified dark squares are opaque against a contrasting clear or white field. State the exact square layout, background finish and viewing side on the drawing; the word positive alone cannot define them.
How many internal corners does a board have?
A complete grid of C square columns and R square rows has (C − 1) by (R − 1) internal corners. Enter the inner-corner count, not the square count, in software that asks for detected corners.
Can the pictured white field be used with backlighting?
Appearance alone does not establish whether the field transmits light. A clear glass or film field can support transmitted illumination; a white backing or opaque ceramic calls for reflected illumination.
Does a smaller square always improve calibration?
No. Pitch must keep corners separately detectable at the working distance, including tilted views and image edges. Flatness, corner positions, focus and lighting also affect the result.
What should be included in an inquiry?
Provide the drawing revision, square pitch, square and inner-corner counts, active area, outline, substrate, pattern side, lighting mode and required inspection record.
Selection notes
Positive checkerboard targets place opaque squares against clear or white regions for compatible camera-calibration illumination.
Define the actual transmitting and opaque regions, border and observing side. A white backing changes illumination behaviour; choose it for the working optical arrangement.
Information for your inquiry
Square pitch, inner-corner count, border, material, backing, viewing side and capture conditions.
Does positive polarity define the detector's point order?
No. Polarity describes contrast. Point order, coordinate origin and row/column conventions must still match the detector and physical coordinate list.