Manual of AVSHD 709 Disc Calibration Patterns -2- APL Clipping
This pattern includes both levels near black and levels near white. The bright bars around white will be discussed later in the White Clipping description. Like the first pattern, this one can also be used for setting black-level (brightness) on a digital display. The idea is similar, you want to adjust the black-level to a dark setting that still retains all intended detail.
You will need to use this pattern in a typical viewing environment. If you often watch the display standing up during the day with a lot of sunlight in the room, that is how you would also view this pattern.
Instead if you watch the display sitting in a chair with little light in the room at night, again that is how you would use this pattern. The reason to begin with a typical viewing environment is because light in the room and viewing location can affect perception. Some displays even include day and night settings, for adjusting the display differently for the each of the above conditions.
If you start by setting the black- level very high you should see the flashing bars in the dark portion of the image. The vertical middle of the dark area flashes reference black (16), and the dark portion of the image near the numbers works like Black Clipping. As you turn down the black-level (brightness) control, the lower numbered bars will blend with the background. Ideally you would want 4-16 to blend together and for levels higher than reference black to remain flashing. The 17 and 18 bars should not be clearly-noticeable, but you should be able to notice the bar marked 19 as it flashes. Turn black-level no lower than the setting where it is possible to see 19-28 flash. Try for just barely being able to see 19 flash in a typical viewing environment.
For some circumstances the black-level setting from Black Clipping agrees with the APL Clipping test, and in other situations the first two patterns return different settings. Any agreement typically depends on items like display performance, room lighting, and viewing location. If you find the first and second patterns clearly require different black-level settings with your room and digital display, an acceptable compromise can be to use the setting you receive from this APL Clipping pattern. You can disregard the setting from the Black Clipping pattern if it does not agree with the APL Clipping test.
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