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Test Pattern

Gamma Value

2.2

Reference Level

Near-Black Steps (0–10)

Count the distinct squares visible. You should see 11 separate levels from 0 (pure black) to 10. If lower levels merge together, reduce your display's brightness setting.

Keyboard: 1-0 for patterns, F for fullscreen, R to reset, ←→ to adjust gamma

Quick Presets:

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About

Incorrect black level calibration causes shadow crushing - detail loss in dark regions where adjacent brightness levels (e.g., 0 vs 5 vs 10 out of 255) become indistinguishable. This degrades photo editing accuracy, video grading fidelity, and gaming visibility. The human eye can theoretically differentiate approximately 10 million colors, yet most consumer displays ship miscalibrated, with brightness set too high and contrast crushing the bottom 5 - 10% of the luminance range.

This tool generates reference patterns conforming to ITU-R BT.709 and sRGB gamma assumptions (γ = 2.2). The near-black step pattern reveals whether your display's brightness control is set correctly - you should see distinct squares from level 1 onward against the 0 background. If levels below 5 - 8 appear identical, reduce your display's brightness setting until separation appears. Conversely, if the 0 background appears gray rather than pure black, brightness is too high, reducing contrast ratio.

Formulas

Display output luminance follows the gamma power function relating input signal to perceived brightness:

L_out = L_max × (V_in255)^γ

Where L_out = output luminance in cd/m², L_max = display peak brightness, V_in = input signal value (0 - 255), and γ = gamma exponent (typically 2.2 for sRGB).

The near-black differentiation test relies on the Weber-Fechner law of perception. The just-noticeable difference (JND) threshold follows:

ΔLL ≈ 0.01 to 0.02

At low luminance levels, absolute differences become vanishingly small. A properly calibrated display at γ = 2.2 produces only 0.03% of peak luminance at input level 5:

(5 ÷ 255)^2.2 = 0.0003 = 0.03%

This explains why shadow detail requires careful brightness calibration - the differences are physically minute and easily masked by elevated black levels.

Reference Data

Test Pattern	Purpose	What to Look For	Calibration Action
Near-Black Steps (0-10)	Shadow detail visibility	Each square distinct from neighbors	Adjust brightness until level 1-2 visible
Full Grayscale Ramp	Gamma linearity	Smooth gradient without banding	Adjust gamma if mid-tones too dark/light
11-Step Grayscale	Quick tonal check	Even spacing between all steps	Reference for contrast adjustment
21-Step Grayscale	Detailed tonal response	No merged adjacent steps	Fine-tune gamma curve
Black/White Flicker	Response time, persistence	Clean transitions, no ghosting	Panel characteristic (not adjustable)
Checkerboard	Pixel uniformity, sharpness	Crisp alternating pattern	Check scaling settings if blurry
Dark Gradient	Low-end banding detection	Smooth transition 0-50	Increase bit depth if banding visible
PLUGE Pattern	Professional black level	Below-black invisible, above-black visible	Industry standard brightness calibration
Gamma 1.8 Test	Mac/Print workflow	Middle gray appears correct	Switch gamma mode if available
Gamma 2.2 Test	sRGB/Windows standard	Middle gray matches 50% luminance	Default for most content
Gamma 2.4 Test	BT.1886/Dark room video	Darker midtones, cinema look	Use for controlled viewing environments
RGB Separation	Color channel black levels	Each channel reaches true black	Adjust individual RGB bias if offset
Zone Plate	Resolution, moiré detection	Clean concentric rings	Detect scaling/compression artifacts
Contrast Ratio	Dynamic range measurement	Visible difference white vs black	Maximize without crushing
Shadow Detail (2%)	Critical shadow visibility	2% above black visible	Professional editing threshold
Black Uniformity	Backlight bleed detection	Even black across screen	Panel quality indicator
Near-White Steps	Highlight clipping	Distinct steps 245-255	Adjust contrast if whites merge
APL 10% Window	OLED ABL behavior	Stable brightness small bright area	Observe auto-dimming response
APL 50% Window	OLED ABL midpoint	Compare to 10% window brightness	Document ABL curve
APL 100% White	Full white capability	Maximum sustainable brightness	Note for HDR content planning

Frequently Asked Questions

Your display's brightness (backlight) setting is too high, causing the black floor to elevate. When minimum luminance exceeds the perceptual threshold between adjacent dark values, they merge visually. Reduce brightness until level 1-2 becomes distinctly visible against pure black. On LCD panels, this may never fully resolve due to backlight bleed limitations - IPS panels typically achieve 1000:1 contrast while VA panels reach 3000:1 or higher.

For sRGB-standard work, target γ = 2.2. This matches the assumed encoding of most consumer content and web imagery. macOS historically used γ = 1.8 for print workflows, though modern versions default to 2.2. For video mastering in controlled dark environments, BT.1886 recommends γ = 2.4. The gamma test patterns in this tool display mid-gray at 50% input value - if it appears too dark, your actual gamma exceeds the target; if too light, gamma is lower.

PLUGE (Picture Line-Up Generation Equipment) uses three vertical bars: one at -2% (below black), one at 0% (reference black), and one at +2% (above black). Adjust brightness until the below-black bar is invisible and indistinguishable from the 0% bar, while the above-black bar remains clearly visible. If you can see the below-black bar, brightness is too high. If you cannot see the above-black bar, brightness is too low. This is the broadcast industry standard method.

Banding indicates insufficient bit depth in the signal chain. An 8-bit display can only render 256 discrete levels per channel. If your graphics card is outputting 8-bit color over a limited connection, or if the display internally processes at 8-bit, posterization becomes visible in gradients. Solutions include: enabling 10-bit output in GPU settings (if supported), using DisplayPort instead of HDMI 1.x, enabling dithering in display settings, or upgrading to a 10-bit panel for professional work.

OLED panels employ Automatic Brightness Limiting (ABL) to prevent overheating and extend lifespan. As the Average Picture Level (APL) increases - meaning more of the screen displays bright content - the panel reduces peak brightness. The APL test windows in this tool (10%, 50%, 100%) reveal this behavior. A small white box may reach 800 cd/m² while a full white screen dims to 200 cd/m². This is normal OLED behavior and not a calibration error.

Perform black level calibration in your typical viewing environment. Ambient light raises the effective black floor through screen reflections, making shadow detail harder to perceive regardless of display settings. However, for establishing baseline calibration, a dark room reveals the panel's true capabilities. Note that glossy screens reflect more ambient light than matte finishes, affecting practical black level perception by 10-50% depending on room brightness.

A full black screen reveals backlight bleed - bright areas, typically in corners or edges, where the backlight escapes despite closed LCD shutters. IPS panels commonly exhibit IPS glow (silver sheen when viewed off-angle) and corner bleed. VA panels show less bleed but may have clouding in the center. No LCD achieves perfect uniformity; variations under 10% are acceptable for consumer use. For professional grading, uniformity under 5% is preferred, often requiring factory calibration.