Originally Posted by markstar
Can someone summarized and most agreed upon method
If you're using the AVS HD 709 patterns, the APL Clipping pattern (Basic Settings - Chapter 2) is intended to be comparable to commercial patterns when you can barely see 19 flash from your typical viewing location with usual room lighting.
where should the back light be set during this?
Set the backlight to whatever setting you want to use for typical viewing.
Both the backlight control and the black-level (brightness) control can affect where you will be able to see flashing on the APL Clipping pattern. There are different approaches for how to go about setting both controls, and it may also depend on the TV. Personally I tend to use the black-level control primarily to set where a digital display clips, and I tend to use the backlight control mainly to adjust the overall image for room lighting. Personally I start by setting the backlight very high to make it easier to see where the first level above the display's black actually begins flashing. On better TVs you may need to make the room entirely dark, use the black clipping pattern, get right up next to the TV, and even then it might be difficult to spot where exactly the flashing starts, but on other TVs it's very easy to tell exactly which levels are being cut off from the black-level (brightness) setting. After I have an idea where the black-level control causes clipping, I turn down the backlight for room lighting. This process of setting black-level first and then adjusting the backlight will not work for all displays, but it's how I would try to demonstrate that the black-level (brightness) control generally has a different function than the backlight control.
Is the second post here still valid?
There are some gaps between the general theory of calibration and how displays actually perform. As a consumer you can buy a number of different types of displays, and generally the displays have some slight differences in how they perform. Basically with calibration the intent is to try to get various displays to look somewhat similar, and in order to do this it's sort of difficult to make absolute rules, since again various displays can perform differently.
- In theory 17 is expected to represent information that is probably imperceptibly lighter than black. Ideally you would not want to cut off this information, but on the other hand the difference against black is likely expected to be smaller than possible on most digital displays.
- Also in theory 20 is expected to be slightly lighter than black. It's rather difficult to show just how much lighter than black using video, and some displays would also vary depending on the exact image displayed.
Realistically many LCD displays come out of black much more quickly than a CRT display would with the exact same input. With some LCD displays you may be able to use room lighting to help mask the relatively poor near-black performance, and in such a case it might be fine to set 17 to flash when viewed near the screen in a completely dark room. Other displays have even worse near-black performance, where the first level above black is clearly visible even with some room lighting, and in such a case it may be a reasonable compromise to try to get the display to look more like other displays by cutting off a bit of information near black. My basic point is that there are not really absolute rules, because different displays do not perform exactly the same. To get two displays to look sort of similar in a side-by-side comparison you may need to set them slightly differently.