OSSC display test suite

Introduction

OSSC display test suite is a special firmware based on v0.81 (non-audio) that extends test pattern functionality. A number of tests have been added which try to recreate some of most challenging aspects retro consoles pose on modern displays. Two new options ("Testpattern mode" and "Testpattern spd.") are placed under "Output opt." menu which enable switching between the tests and configuring them. Below are short descriptions for each category and test.

Basic compatibility tests

The tests in this category help verifying whether a monitor supports standard SDTV/EDTV modes. The tests also provide means for testing whether a monitor decodes HDMI AVI Inforframe "RGB Quantization Range" and "Scan Information" parameters. If interpreted correctly, the sink should treat the signal as full-range RGB with no overscan which can be verified by checking that 32 distinct bars in the greyscale can be identified and that a checkerboard pattern with at least 16 squares in each side surrounds the grey area in the middle.

T1: 480p STD

Basic test at standard 480p@59.94Hz rate

T2: 576p STD

50Hz mode compatibility test

T3: 480i STD

Interlace compatibility test

T4: 576i STD

Interlace compatibility test for 50Hz

Image retention tests

Bob deinterlacing triggers temporary image retention on vairous LCD panels which is a surprising result for many as LCD is generally considered mostly immune to retention. The tests emulate bob deinterlacing to reveal whether a panel is prone to it. The tests should be displayed for around 5 minutes and then monitor should be switched to another source, preferably something with a solid light background. If traces of the test pattern are still visible after changing input, it indicates that the panel is suspect to image retention.

T5: 480p Bob

Test pattern is shifted up/down by one pixel every frame, emulating bob deinterlacing of a 480i source

Refresh rate tests

Many classic game consoles do not operate exactly at standard 59.94/60/50Hz refresh rate, especially if typical 50/60Hz modifications have been applied on them. Moreover, there are systems that use refresh rates way outside what is common today. The tests help identifying how well a monitor can handle these off-spec rates by displaying a moving checkerboard box at non-standard refresh rates. In ideal case, the monitor is able to sync each mode and display it without any judder resulting from internal framerate conversion.

These tests also provide means for observing the amount of eye tracking motion blur. On low-persistence displays such as CRT and plasma, appereance of the checkerboard pattern should remain mostly intact when viewed with increasing speeds (adjusted via "Pattern spd." option). With a sample-and-hold type display (e.g. LCD/OLED without blur reduction), black squares of the pattern first start to turn towards grey on the viewer's eye when speed is increased, eventually making the pattern unrecognizable at the highest setting. 60Hz is not high enough refresh rate for displaying fast motion clearly without tradeoffs, but ideally a gaming monitor/TV should provide options to improve motion e.g. by backlight strobing, black frame insertion, rolling scan and/or motion interpolation.

T6: 480p@59.5Hz

Test refresh rate which is slightly below NTSC standard

T7: 480p@60.5Hz

Test refresh rate which is slightly above NTSC standard

T8: 480p@55Hz

Test refresh rate which is used by certain arcade boards

T9: 400p@70Hz

Test 640x400@70Hz (VGA mode 13) which is typically used by DOS games

Other tests

T10: 960p

Test compatibility of 2x2 multiplication which OSSC is able to perform for 480p sources