Pixel Grid Test

What Each Display Test Pattern Reveals About Your Monitor — Geometry Grid and Beyond

A well-designed alignment grid is just the beginning. This tool provides over 200 distinct evaluation images arranged in logical groups, each targeting a specific aspect of visual quality. Understanding what each image diagnoses transforms a simple panel pass into a thorough performance assessment of your panel's hardware and display quality. Below is an overview of every major image group, followed by detailed guidance on interpreting your results. The free convergence test is free and runs entirely client-side, so nothing about your display is ever uploaded.

Pixel Grid — Spotting Dead and Stuck Pixels

The pixel grid test image renders alternating lit and unlit dots in a single-dot checkerboard arrangement — every other dot is white, every adjacent dot is black. Because each dot is addressed individually, any defective dots that fail to switch state are immediately visible as anomalies in the regular grid. A dead pixel appears as a persistent dark dot that never illuminates regardless of the image displayed; on a liquid-crystal panel, this typically means the LC element is physically broken or the thin-film transistor has failed. A stuck pixel is the opposite: it remains locked in an active state, glowing as a lit dot in red, green, blue, or white even when the surrounding dots are switched off.

The fine pixel checkerboard also reveals sub-dot defects — cases where only one tonal channel within a single dot fails. On RGB flat panels and emissive screens, each dot contains three sub-elements (red, green, blue). A partial sub-pixel failure causes the dot to render an incorrect hue rather than the intended tone, which becomes obvious against the uniform grid background. The dot-contrast checkerboard variant — alternating white on black squares with black on white squares — further stresses sub-dot addressing. This is distinct from the single-dot checkerboard in that it evaluates edge convergence between adjacent dot clusters rather than individual dot switching. The 1920 × 1080 version of this image is particularly useful for FHD panels, while the 1280 × 960 variant covers legacy XGA and SXGA formats.

Worked example — stuck green dot: A user sets their panel to the uniform red fill image. Against the fully red surface, a single dot emitting green light is immediately obvious because its hue is completely wrong relative to the surrounding tone. The user confirms the finding by switching to a uniform blue fill — the anomalous dot now appears cyan (a mix of its stuck green sub-element and the blue fill), confirming it is a stuck dot with a sub-element failed in the green channel. Cycling hues through the full uniform fill sequence and observing whether the defective dot changes tone helps distinguish between a fully stuck dot and a partial sub-element defect. If the dot responds to any image, it may recover after extended hue cycling across the panel.

Solid Colors — Checking Backlight Bleed and Uniformity

Full-panel uniform fills — including a bright white field, a dark fill, a mid-grey fill, red, green, and blue hue fills — are the most fundamental images in any dark-dot check suite. Each fill eliminates the complexity of a multi-tone scene and forces every dot on the panel to reproduce one target value, making deviations immediately visible to the human eye.

The all-dark fill is the most critical for identifying backlight bleed — a problem most common on edge-lit flat panels where light from the backlighting array leaks around the border edges and illuminates the corners or edges of an otherwise dark image. To perform this check accurately, dim the room lights, allow your eyes to adjust, and look for uneven bleed edges or patches of grey luminance near the panel borders. Light leakage is different from non-illuminating dots — it is a structural property of the panel's lighting system rather than a dot-level defect. Emissive panels are immune to backlight bleed but may exhibit other uniformity issues.

The uniform grey field and mid-grey images expose backlight uniformity and panel-uniformity issues that are invisible against pure dark or bright fills. Patches, banding, or tonal gradients across the grey fill indicate that the panel's backlighting is not producing even illumination across the full surface area — a common quality-control issue on budget flat panels.

Worked example — light leakage on a portable computer: The owner opens the all-dark fill image, presses F11 to enter fullscreen mode, and dims the room lights. In the darkened environment, they notice clear bleed edges at all four corners — arcs of grey-white light emanating inward from the border edges. This is classic IPS glow or edge-lit backlight bleed, and is now documented evidence they can use in a warranty dispute. The manufacturer's technical specifications allow a certain number of dot defects under ISO standards, but structural light leakage beyond a defined threshold is grounds for a replacement claim.

Black & White Patterns — Contrast and Brightness Evaluation

The black & white evaluation images — including alternating dark and bright full-panel fills, the ANSI contrast chart, and the checkerboard pattern — evaluate your panel's ability to render the extremes of its luminance range simultaneously. A high-quality panel renders pure black with virtually no light output (dark floor close to zero) and pure white at its maximum rated output level. The ratio between these two values defines the luminance ratio, a key specification for image fidelity in photography, video editing, and gaming.

The checkers board and dot-luminance images place dark and bright regions in close proximity, revealing whether your panel suffers from blooming — where a bright region elevates the perceived luminance of adjacent dark dots. On flat panels, local dimming zones can introduce this effect. The tonal chart also serves as an effective tonal evaluation for verifying that dark detail remains visible near the dim end of the luminance scale and that highlights are not clipped at the bright end.

Color Bars — Verifying Color Accuracy

The color bars group provides a comprehensive set of images for evaluating your panel's hue rendering across the full visible spectrum. Standard broadcast hue bars in SMPTE, EBU, and similar formats present fully saturated red, green, blue, cyan, magenta, and yellow bars at defined digital video level values — any panel that is correctly calibrated will render these at consistent hue, saturation, and luminance from left to right and top to bottom. The hue reference image goes further, presenting spectrum saturation ramps, tonal patches, inner circle and outer circle elements from the hue-circle family, and a hue triangle for gamut boundary verification.

The hue step and step-wipe images evaluate whether your panel can resolve discrete tonal steps within each primary hue — a proxy for effective tonal depth and bit-depth accuracy in the panel's signal processing. Gradient banding (visible steps instead of a continuous tone across a hue gradient) indicates that the panel's bit depth or dithering algorithm is insufficient for smooth hue rendering. The hue-wipe, half-wipe, and full-wipe variants further stress transitions between tones to expose metamerism failures — cases where two physically different stimuli appear identical, indicating a narrowed tonal space.

Worked example — hue accuracy check for a content creator: A video editor preparing to grade broadcast footage uses the hue-bar image to verify their panel produces accurate, consistent hues before beginning work. They compare the rendered tones against their external hue reference and confirm that the primary channels are balanced without a noticeable shift. They then run the tonal-step and tonal-gradient images to check for banding in the shadow and highlight rolloff regions — confirming that their 10-bit IPS panel achieves a continuous tone with no hard steps, making it suitable for professional grading with accurate HSL and HSV tonal-space reproduction.

Brightness Test — Gradient and Luminance Range

The luminance and tonal-gradient images present continuous ramps from absolute black to peak white, plus intermediate steps for evaluating dark detail and highlight retention. A correctly calibrated panel shows every step in a grayscale wedge as a distinct, visually separate tone — neither crushing the darkest steps into a uniform black block nor clipping the brightest steps into featureless white. The tonal-span check in the lights-and-shadows configuration uses split-field images that place near-black and near-white content side by side, revealing whether the panel compresses either end of the tonal span.

Look for gradient banding — visible discrete steps instead of a continuous tone — which indicates limited bit depth or poor dithering in 8-bit panels. A banding evaluation across a dark grey ramp is especially revealing: most 6-bit-plus-dithering panels show visible contouring in shadow regions that true 8-bit or 10-bit panels do not. The gamma checker and gamma lines images verify that your panel's gamma response curve matches the target (typically gamma 2.2 for sRGB content or gamma 2.4 for broadcast). Incorrect gamma causes the overall image to appear either too luminous or too dim without affecting peak output, a common reason for video calibration discrepancies. The gamma evaluation images developed for this tool use alternating fine lines and solid patches to make perceptual differences between gamma settings visible without specialist equipment.

Common Display Issues the Test Can Detect

Beyond non-illuminating dots and locked-on dot defects, a thorough panel evaluation using the full set of images reveals a wide range of panel defects and calibration issues that affect image fidelity in everyday use:

• Dead dot / dark dot: A dot that never illuminates — appears as a persistent single black square or dark dot on a bright-fill image. On a liquid-crystal panel, this represents a permanently off element.
• Lit dot / locked-on dot: A dot that remains permanently lit at full output in one hue — most visible against a uniform dark fill. Emissive panels are particularly susceptible to permanently lit dots due to their self-emissive dot structure.
• Partial sub-pixel / sub-element failure: One sub-element within a dot fails, causing a hue tint — detectable by cycling through uniform red, green, and blue fills and observing which hue the anomalous dot adopts.
• Backlight bleed / bleed edges: Light leaking around border edges on flat panels — visible only during the dark fill in a darkened room.
• Uniformity / backlight-uniformity issues: Uneven luminance across the grey field — visible as luminance variations, patches, or tonal patches across the panel's surface.
• Geometric error / overscan / convergence: Straight lines that appear curved or misaligned — detectable with the alignment grid, rule bars, and geometry checkers images. Edge convergence and convergence-check images confirm alignment of hue sub-elements at the border edges. CRT surfaces can also be evaluated for convergence, overscan check, and distortion check using these alignment lines and geometry-point tests.
• Mapping distortions / clipping: When the panel's output format doesn't match the image's intended dimensions, dot scaling causes blurring in the single-dot line elements of the checkerboard. A clipped frame at the edges indicates overscan is enabled, cutting off image content near the border.
• Image artifacts / hue shift: Systematic tonal error across the panel — identifiable with the comprehensive hue reference image and hue-shift evaluation, which cycle through random hues and composite images to expose systematic rendering errors in the panel's signal processing or video signal chain. These can also originate from the cable or adapter — switching panel cables after a positive result isolates whether the artifact is a panel defect or a signal chain issue.

Comprehensive Pattern Groups and What They Diagnose

The full set of monitor test patterns — including broadcast evaluation images for TV sets and reference images covering every aspect of panel performance — is organised into image groups to make a complete display diagnostic systematic and efficient. The quick-check images provide an overall assessment in under a minute: a bright fill for dark dots, a dark fill for lit dots and light leakage, a grey field for uniformity, and a tonal-gradient image for banding. The comprehensive images go further, addressing gamma evaluation, output-format verification, hue evaluation, overscan check, distortion check, convergence check, and dot-level clarity through the high-density alignment grid and single-dot checkerboard images.

For professional panel evaluation, the tool provides image files in common output formats: FHD 1920×1080, QHD 2560×1440, 4K UHD 3840×2160, 1280×720, 1280×960, and legacy formats. Inverse images — where each base image is rendered with dark and bright areas swapped — allow you to verify that a detected anomaly is truly a dot defect rather than a rendering artifact introduced by the image itself. Format-identifier overlays embedded in some check images confirm that the correct full-size images are displayed at the intended output format without unintended scaling. All image files are available as uncompressed files in zip archives grouped by output format, making offline panel setup and monitor check workflows straightforward for quality-control environments and display-tech professionals.

Whether you're performing a quick dark-dot check, a full monitor calibration, or a professional complete display diagnostic before buying used gear or filing a warranty dispute on a new monitor, this 4-step evaluation and its extended image set give you the visual tools to identify every category of panel defect with confidence. The tool works equally well on portable computers, all-in-ones, desktop monitors, and TV sets — making it the most accessible and comprehensive panel evaluator available as a browser-based online test in 2025.