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Company News >> Manual of AVSHD 709 Disc Calibration Patterns -3-White Clipping

 This very high APL pattern can be used to observe clipping near white on digital displays. The video is intended for adjusting white- level, which may be called contrast or picture on your TV. Because of the very high APL of this pattern, you may also want to look at the levels near white from APL Clipping. Both patterns function similarly, and for simplicity we will only discuss white-level once with this pattern.

If you start by lowering the white-level control you should see a number of vertical flashing bars. If you see no flashing at all, then one of your electronic devices may be clipping near white. The APL Clipping pattern includes more levels below reference white if you are unable to see any flashing with this pattern. Typically that should not be an issue, but if you run into a situation where lowering white-level at the display does not begin to show any flashing on either pattern, then you need to troubleshoot to find if the player or another device is clipping the signal.


Our suggestion will be to avoid any clipping before the signal gets to the display, to ensure the best video quality possible. That means if you turn down white-level at the display, and turn off any clipping controls a few TVs may have, ideally you want to be able to see the bars above 235 flash to make sure the entire signal reaches the display. Some players, such as computers or the PlayStation 3, by default might not pass the entire signal, and in the case of the PS3 the Super-White setting must be turned on to output the entire range. Some receivers have been reported to clip, and in that case you might never be able to see levels 235-253 flash without updating the equipment or refraining from passing the video through the device. Most importantly you should always see flashing for bars numbered 230-234 with this pattern on digital displays, but if possible it may be preferable if your electronics allow you to see the vertical bars numbered higher than white (235) flash with this pattern when turning down white-level at the display.

Generally you want to set white-level to a high setting where the brightest parts of the image look white. Increasing white-level may make white brighter, but you want to make sure it does not also introduce any detrimental effects. Our suggestion is that you begin with a low setting, and as you increase white-level watch for clipping, discoloration, and eye fatigue. The following will consider each of those items that might require lowering white-level, and additional white-level topics will be mentioned later in the Misc. Patterns A descriptions.

Clipping – Start with a low setting. As you increase white- level, watch to see if any of the flashing bars disappear. Different electronics may limit how much the white -level control can affect the image. Your controls should meet with one of the following three scenarios.

·Some displays will show all the bars even on their highest setting. If your electronics still show all the bars at maximum, then clipping is good with the highest setting.

·If white-level on your display can cause bars to stop flashing, we suggest keeping some bars above reference white. A good compromise for displays that show levels above white may be setting white-level so you can still see 244 flash.

·At minimum 230-234 should always flash. If you cannot see 230-234 flash, then you need to turn down white-level until the levels below reference white flash. Seeing adjacent levels flash can be difficult, so if your display only goes to reference white (235), it may be very hard to notice 234 flash.

Discoloration – You will want to see if you can notice any change in the shade of grays near white as you adjust the white-level setting. With some displays increasing white -level beyond a point may cause whites to begin to have a pinkish or other colored tint. If you cannot spot a change in the shade of gray near white by lowering white-level, then the check for discoloration is fine.

Eye fatigue – You could watch a movie to make sure whites appear relatively bright and you do not encounter eye strain. Eye strain when watching would indicate the display is too bright for the light in the room, and you may need to dim the display. If your display seems too bright and has a backlight setting or iris control, you should typically try turning those settings down before lowering white-level. Lowering backlight related settings will also give darker blacks as white is dimmed. If the display remains too bright after looking for backlight, iris, or other lighting controls, then white-level could also be lowered to avoid eye fatigue from whites being too bright.