SUMMARY On my OLED screen I use as much black as possible (wallpaper, dark mode). With kwin-6.3.3 I noticed that in SDR mode my "solid color: black" wallpaper appears to have a faint gray. Switching to HDR mode has proper true black again. This is with no ICC profile configured and "Prefer efficiency" set. Though toying with either didn't appear to change anything. Reminds me of a https://bugs.kde.org/show_bug.cgi?id=494854 - except likely no vk_hdr_layer involved. STEPS TO REPRODUCE 1. Own an OLED 2. Display black in SDR mode 3. Turn down external light sources in your room OBSERVED RESULT See the whole screen faintly glowing EXPECTED RESULT Only the mouse cursor should emit light SOFTWARE/OS VERSIONS Operating System: Arch Linux KDE Plasma Version: 6.3.3 KDE Frameworks Version: 6.12.0 Qt Version: 6.8.2 Kernel Version: 6.13.6-arch1-1 (64-bit) Graphics Platform: Wayland Processors: 16 × AMD Ryzen 7 PRO 4750U with Radeon Graphics Memory: 46.3 GiB of RAM Graphics Processor: AMD Radeon Graphics
Can't replicate that on my LCD's backlight dimming, though the brightness levels they turn on might be different from OLED. Please attach the output of kscreen-doctor -o
(In reply to Zamundaaa from comment #1) > Can't replicate that on my LCD's backlight dimming, though the brightness > levels they turn on might be different from OLED. > > Please attach the output of kscreen-doctor -o SDR: Output: 4 HDMI-A-1 enabled connected priority 1 HDMI Modes: 91:3840x2160@60*! 92:4096x2160@120 93:4096x2160@120 94:4096x2160@100 95:4096x2160@60 96:4096x2160@60 97:4096x2160@50 98:4096x2160@30 99:4096x2160@30 100:4096x2160@25 101:4096x2160@24 102:4096x2160@24 103:3840x2160@120 104:3840x2160@120 105:3840x2160@100 106:3840x2160@60 107:3840x2160@60 108:3840x2160@50 109:3840x2160@30 110:3840x2160@30 111:3840x2160@25 112:3840x2160@24 113:3840x2160@24 114:2560x1440@120 115:1920x1200@60 116:1920x1080@120 117:1920x1080@120 118:1920x1080@100 119:1920x1080@60 120:1920x1080@60 121:1920x1080@60 122:1920x1080@50 123:1920x1080@30 124:1920x1080@30 125:1920x1080@25 126:1920x1080@24 127:1920x1080@24 128:1600x1200@60 129:1680x1050@60 130:1280x1024@60 131:1440x900@60 132:1280x800@60 133:1152x864@60 134:1280x720@60 135:1280x720@60 136:1280x720@50 137:1024x768@60 138:800x600@60 139:720x576@50 140:720x480@60 141:720x480@60 142:720x480@60 143:720x480@60 144:640x480@60 145:640x480@60 146:720x400@70 147:1600x1200@60 148:1280x1024@60 149:1024x768@60 150:2560x1600@60 151:1920x1200@60 152:1280x800@60 153:3840x2160@60 154:3200x1800@60 155:2880x1620@60 156:2560x1440@60 157:1920x1080@60 158:1600x900@60 159:1368x768@60 160:1280x720@60 Geometry: 0,0 3840x2160 Scale: 1 Rotation: 1 Overscan: 0 Vrr: Always RgbRange: unknown HDR: disabled Wide Color Gamut: disabled ICC profile: none Color profile source: sRGB Color power preference: prefer efficiency and performance Brightness control: supported, set to 100% and dimming to 100% HDR: Output: 4 HDMI-A-1 enabled connected priority 1 HDMI Modes: 91:3840x2160@60*! 92:4096x2160@120 93:4096x2160@120 94:4096x2160@100 95:4096x2160@60 96:4096x2160@60 97:4096x2160@50 98:4096x2160@30 99:4096x2160@30 100:4096x2160@25 101:4096x2160@24 102:4096x2160@24 103:3840x2160@120 104:3840x2160@120 105:3840x2160@100 106:3840x2160@60 107:3840x2160@60 108:3840x2160@50 109:3840x2160@30 110:3840x2160@30 111:3840x2160@25 112:3840x2160@24 113:3840x2160@24 114:2560x1440@120 115:1920x1200@60 116:1920x1080@120 117:1920x1080@120 118:1920x1080@100 119:1920x1080@60 120:1920x1080@60 121:1920x1080@60 122:1920x1080@50 123:1920x1080@30 124:1920x1080@30 125:1920x1080@25 126:1920x1080@24 127:1920x1080@24 128:1600x1200@60 129:1680x1050@60 130:1280x1024@60 131:1440x900@60 132:1280x800@60 133:1152x864@60 134:1280x720@60 135:1280x720@60 136:1280x720@50 137:1024x768@60 138:800x600@60 139:720x576@50 140:720x480@60 141:720x480@60 142:720x480@60 143:720x480@60 144:640x480@60 145:640x480@60 146:720x400@70 147:1600x1200@60 148:1280x1024@60 149:1024x768@60 150:2560x1600@60 151:1920x1200@60 152:1280x800@60 153:3840x2160@60 154:3200x1800@60 155:2880x1620@60 156:2560x1440@60 157:1920x1080@60 158:1600x900@60 159:1368x768@60 160:1280x720@60 Geometry: 0,0 3840x2160 Scale: 1 Rotation: 1 Overscan: 0 Vrr: Always RgbRange: unknown HDR: enabled SDR brightness: 150 nits SDR gamut wideness: 0% Peak brightness: unknown Max average brightness: unknown Min brightness: 0 nits Wide Color Gamut: enabled ICC profile: none Color profile source: sRGB Color power preference: prefer efficiency and performance Brightness control: supported, set to 100% and dimming to 100% It's really faint, almost unnoticeable - much lower luminance iirc than with 494854.
Just an update. I tried the same display/cable/kwin version using a USB-C HDMI Adapter, and the OLED screen stays properly black even in SDR mode. Output: 2 DP-2 enabled connected priority 1 DisplayPort replication source:0 Modes: 14:3840x2160@60*! 15:4096x2160@120 16:4096x2160@120 17:4096x2160@100 18:4096x2160@60 19:4096x2160@60 20:4096x2160@50 21:4096x2160@30 22:4096x2160@30 23:4096x2160@25 24:4096x2160@24 25:4096x2160@24 26:3840x2160@120 27:3840x2160@120 28:3840x2160@100 29:3840x2160@60 30:3840x2160@60 31:3840x2160@50 32:3840x2160@30 33:3840x2160@30 34:3840x2160@25 35:3840x2160@24 36:3840x2160@24 37:2560x1440@120 38:1920x1200@60 39:1920x1080@120 40:1920x1080@120 41:1920x1080@100 42:1920x1080@60 43:1920x1080@60 44:1920x1080@60 45:1920x1080@50 46:1920x1080@30 47:1920x1080@30 48:1920x1080@25 49:1920x1080@24 50:1920x1080@24 51:1600x1200@60 52:1680x1050@60 53:1280x1024@60 54:1440x900@60 55:1280x800@60 56:1152x864@60 57:1280x720@60 58:1280x720@60 59:1280x720@50 60:1024x768@60 61:800x600@60 62:720x576@50 63:720x480@60 64:720x480@60 65:720x480@60 66:720x480@60 67:640x480@60 68:640x480@60 69:720x400@70 70:1600x1200@120 71:1280x1024@120 72:1024x768@120 73:2560x1600@60 74:2560x1600@120 75:1920x1200@120 76:1280x800@120 77:3200x1800@60 78:3200x1800@120 79:2880x1620@60 80:2880x1620@120 81:2560x1440@60 82:1600x900@60 83:1600x900@120 84:1368x768@60 85:1368x768@120 86:1280x720@120 Geometry: 0,0 3840x2160 Scale: 1 Rotation: 1 Overscan: 0 Vrr: incapable RgbRange: Automatic HDR: disabled Wide Color Gamut: disabled ICC profile: none Color profile source: sRGB Color power preference: prefer efficiency and performance Brightness control: supported, set to 100% and dimming to 100% Color resolution: 10 bits per color, range: [8; 16] bits per color Allow EDR: unsupported back with SDR on the HDMI 2.0 port, it's still lightly glowing: Output: 4 HDMI-A-1 enabled connected priority 1 HDMI replication source:0 Modes: 78:3840x2160@60*! 79:4096x2160@120 80:4096x2160@120 81:4096x2160@100 82:4096x2160@60 83:4096x2160@60 84:4096x2160@50 85:4096x2160@30 86:4096x2160@30 87:4096x2160@25 88:4096x2160@24 89:4096x2160@24 90:3840x2160@120 91:3840x2160@120 92:3840x2160@100 93:3840x2160@60 94:3840x2160@60 95:3840x2160@50 96:3840x2160@30 97:3840x2160@30 98:3840x2160@25 99:3840x2160@24 100:3840x2160@24 101:2560x1440@120 102:1920x1200@60 103:1920x1080@120 104:1920x1080@120 105:1920x1080@100 106:1920x1080@60 107:1920x1080@60 108:1920x1080@60 109:1920x1080@50 110:1920x1080@30 111:1920x1080@30 112:1920x1080@25 113:1920x1080@24 114:1920x1080@24 115:1600x1200@60 116:1680x1050@60 117:1280x1024@60 118:1440x900@60 119:1280x800@60 120:1152x864@60 121:1280x720@60 122:1280x720@60 123:1280x720@50 124:1024x768@60 125:800x600@60 126:720x576@50 127:720x480@60 128:720x480@60 129:720x480@60 130:720x480@60 131:640x480@60 132:640x480@60 133:720x400@70 134:1600x1200@120 135:1280x1024@120 136:1024x768@120 137:2560x1600@60 138:2560x1600@120 139:1920x1200@120 140:1280x800@120 141:3200x1800@60 142:3200x1800@120 143:2880x1620@60 144:2880x1620@120 145:2560x1440@60 146:1600x900@60 147:1600x900@120 148:1368x768@60 149:1368x768@120 150:1280x720@120 Geometry: 0,0 3840x2160 Scale: 1 Rotation: 1 Overscan: 0 Vrr: Automatic RgbRange: Automatic HDR: disabled Wide Color Gamut: disabled ICC profile: none Color profile source: sRGB Color power preference: prefer efficiency and performance Brightness control: supported, set to 100% and dimming to 100% Color resolution: 10 bits per color, range: [8; 16] bits per color Allow EDR: unsupported in HDR mode with HDMI there is no issue still. Is there anything else I could try or change?
Toying around with the settings I could lower the black levels of the TV. Maybe the differences between HDR/SDR and adapters is related to full/limited range and/or 8b/10b. Closing this as resolved now.
It's certainly possible that the TV does different things with different bit depth, yeah. Thanks for following up on the bug report.