ScreenTestPro What this monitor color test checks
Even an expensive IPS or OLED monitor looks washed out or murky if its black floor, highlight ceiling, tone curve (gamma) or GPU color range is misconfigured. Instead of testing only solid primary colors, this tool renders four precision calibration patterns directly onto an uncompressed HTML5 canvas:
- 256-step RGB and greyscale ramps to expose 6-bit FRC dithering artifacts, compressed GPU LUTs and color banding.
- Near-black squares (RGB 1 to 20 on RGB 0) to catch crushed shadows or an HDMI Limited (16–235) dynamic range mismatch.
- Near-white squares (RGB 235 to 254 on RGB 255) to detect highlight clipping when monitor Contrast is pushed too high.
- A 50% luminance gamma chart (γ 1.8 to 2.6) comparing fine black-and-white dither lines against solid grey patches.
Before you start
- Turn off Windows HDR / macOS High Dynamic Range while testing SDR calibration, or note that HDR tone-mapping overrides your monitor's OSD gamma and contrast controls.
- Set browser zoom to 100% and sit dead-center so the 1-pixel horizontal reference lines in the Gamma chart map cleanly to physical pixel rows.
- Disable Night Light, True Tone and third-party LUT overlays (f.lux, Razer Synapse, gaming "FPS/Cinema" color enhancers).
How to run the test
- Gradient banding (Tab 1): Inspect the greyscale, red, green and blue ramps from left (0) to right (255). Look for sharp vertical ridges or false purple/green tints inside the grey bar.
- Black level (Tab 2): In a dim room, find the lowest numbered grey square you can distinguish from the pure black background. On a properly configured Full-range (0–255) display, squares down to RGB 2 or RGB 3 should be faintly visible.
- White saturation (Tab 3): Find the highest square visible against the pure white background. You should see up to RGB 253 or 254.
- Gamma (Tab 4): Squint slightly or lean back 80 cm and find the column where the striped left half blends seamlessly into the solid right half. For web, photography and PC gaming, that column should be γ 2.2.
- Select your four readings above to get targeted OSD and GPU driver fixes.
How to read your results
| Symptom on Test | Root Cause | Exact Fix |
|---|---|---|
| Squares RGB 1–15 are completely invisible; RGB 17 suddenly pops out | HDMI Limited (16–235) vs Full (0–255) range mismatch | In NVIDIA Control Panel → Change resolution → Output dynamic range: Full (or AMD Adrenalin → Pixel Format: RGB 4:4:4 Full PC) |
| Pure black looks milky grey and washed out across the whole screen | Monitor expects Full (0–255) but GPU is sending Limited (16–235) | Set both GPU driver and monitor OSD ("HDMI Black Level" / "RGB Range") to Full / Normal |
| White squares RGB 248–254 merge into the background | Monitor Contrast control pushed too high | Lower OSD Contrast from 80–100% back to the native center point (usually 50% or 70%) |
| Gamma matches at 1.8 (washed out) or 2.6 (too dark) | Wrong OSD gamma curve or Windows ICC profile | Select Gamma 2.2 (or Mode 1 / Standard) in the monitor OSD |