HD Testchart - Follow artefacts through HD post-production
Version:The idea of the following testchart is to follow artefacts through HD post-production. The artefacts include color transcoding errors, framing errors, subsampling and compression artefacts. The computer generated file is encoded in 8bit RGB space and available as a TIFF file.
Operating System: Mac OS X
The file can be imported to a HD-NLE system and inserted into HDCAM tape before processing (these encoding processes will already alter the content). The chart can then be examined by eye, on the waveform monitor and be exported back to an RGB file to be compared in an image processing program.
The testchart is availabe for the following screen resolutions:
· 1920 * 1080 download/testchart.tif (396 KB)
· 1280 * 720 download/testchart720.tif (216 KB)
· 720 * 576 (PAL) download/testchartpal.tif (152 KB)
· 720 * 486 (NTSC) download/testchartntsc.tif (126 KB)
· 720 * 480 (NTSC DV) download/testchartntscdv.tif (126 KB)
Here are some key features of "HD Testchart":
· The green triangles at the edges show full frame limits, so you can easily detect overscan on the monitor, and cropping on downconversion or on file conversion.
· The horizontal green lines show cropping to film out 1.85, if you apply it symmetrically.
· The vertical green lines show cropping to film out 1.66, if you apply it symmetrically.
· The green rectangle shows safe title area (10% on each side).
· Full size color bars are 75%: white is at 235, black at 16, colors at 180 each.
· 100% color bars are provided on the bottom right: white is at 235, black at 16, colors at 235 each.
· 100% color bars downconverted to composite PAL or NTSC would exceed limits.
Super white and super black
· The super white regions show super white (255), whites near super white and white (235).
· File conversion should preserve super white area, but some algorithms may remap 16-235 to 0-255. You should be able to measure a difference between 255 and 251 on the waveform. On an aligned video-monitor, you should see a difference between 231 and 235, but regions above 235 may appear uniform if clipping occurs.
· The super black regions show super black (0) and the blacks near super black and black (16).
· Black below 16 is not a useable area. Some conversions clip below 16, some remap and some preserve. On an aligned video-monitor, you should see a difference between 16 and 20, but 16 should look the same with numbers below (4,8,12).
· On the bottom left, a gray scale is provided with 8 steps from 0% to 100%. The numeric values (rounded) are: 16, 43, 71, 98, 126, 153, 181, 208, 235.
· The gray scale will show you gamma corrections applied to the image. With a gamma correction over 1.0, gray value will be higher than nominal, with a peak in the difference on the 126-tab. If the peak is on the 71-tab, then probably a black stretch has been applied.
Horizontal and vertical resolution
· The black and white lines show horizontal and vertical resolution in number by scan lines. A second area is displaced by one line at the same resolution to detect eventual phase artefacts.
· You may detect compression and resampling and generation-loss artefacts.
· Horizontal loss in resolution is normal with HDCAM-codec, but there should not be loss in vertical resolution.
· The red and cyan lines will show color subsampling.
· A standard HD-SDI signal at 4:2:2 subsampling will show reduced horizontal resolution.
· The black and white ramp can detect histogram defects (posterization) due to color correction. The ramp is slightly off horizontal to better detect the effect visually.
· The blue ramp also detects errors due to color space conversion in 8bit resolution.
Color space encoding tabs
· The encoding tabs allow to verify if 609 (SD) or 709 (HD) matrices were used to encode component from RGB.
· The red, green and blue tabs all should have the same luma value, if the correct matrices were used.
Note on monitors
· Some aspects of the test chart may be detected by eye both on aligned video monitors and computer monitors. You should however be aware, that specifications of both type of monitors vary in different ways:
· Frame is overscanned on video monitors.
· Frame is often displayed interlaced (or sequential frame) on video monitors.
· Pixel aspect ratio is not square on SD monitors.
· Phosphor specification is different between computer, SD and HD monitors.
· Setup, gain and gamma are different.
Note on waveform and vectorscope instruments
· The primary purpose of the testchart is to measure its values digitally, with an eydroper tool. Some intelligence was used to layout the color patches in a way that the do not disturb each other too much on a waveform monitor, but the task was rather difficult.