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Two display inventions reveal Apple's work on Content-Dependent Brightness Adjustment & Cancelling the Ghosting Phenomena

1 cover  MacBook Pro


Last Thursday the US Patent & Trademark Office published two patent applications from Apple that relate to electronic devices with displays. In the key patent, Apple's invention relates to displays with content-dependent brightness adjustment. The second patent relates to a cancellation architecture for cancelling the ghosting phenomena.


Content-Dependent Brightness Adjustment


Apple notes in a new patent application that if care isn't taken, displays may be damaged by displaying bright content for prolonged periods of time, displays may be operated with brightness levels that consume excessive power, user preferences may not be taken into account when adjusting display brightness, and displayed content may exhibit visible artifacts. Addressing these concerns while displaying content with a pleasing appearance is challenging.


Apple's invention and solution covers control circuitry in an electronic device that may be used in implementing a tone mapping engine. The tone mapping engine may select a content-luminance-to-display luminance mapping to be used in displaying content on the display from the content generator.


The content-luminance-to-display-luminance mapping may be characterized by tone mapping parameters such as a black level, a white level, and/or a peak brightness setting.

During operation, the tone mapping engine may adjust the tone mapping parameters based on ambient light levels and image content. For example, the control circuitry may analyze frames of display data to determine an average pixel luminance level, a median pixel brightness level, or other pixel brightness parameter associated with image content.


Low average pixel luminance levels correspond to mostly dark image content, whereas high average pixel luminance levels correspond to mostly light image content.


When an electronic device is outdoors and displaying mostly dark images with low average pixel luminance levels, the control circuitry may take advantage of the display's maximum achievable brightness to improve readability.


When an electronic device is outdoors and displaying mostly light images with high average pixel luminance levels, the control circuitry may scale the maximum allowable brightness down to reduce power consumption.


The control circuitry may reduce the maximum allowable brightness of the display by multiplying a brightness scaling factor (e.g., ranging from 0 to 1) with the maximum achievable brightness of the display.


The control circuitry may determine the brightness scaling factor based on the average pixel luminance levels. For example, a greater amount of white or light content in an image may use a lower brightness scaling factor (and thus a lower peak allowable brightness) to conserve power.


If desired, the control circuitry may only impose this type of content-dependent peak brightness adjustment when the user has enabled such a feature (e.g., when the user has enabled a dark viewing mode in which images are inverted or partially inverted so that the images are mostly dark content).


Apple's patent FIG. 1 is a schematic diagram of an illustrative electronic device having a display with technologies supporting content-dependent brightness adjustment.


2 Apple patent fig. 1 tone mapping


While Apple may have a specific device display this invention may first debut on, Apple buries it within a long list of possible devices the invention may work with such as: "a laptop computer (MacBooks), a computer monitor containing an embedded computer (iMac), a tablet computer (iPad), a cellular telephone (iPhone), a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device (Apple Watch), a pendant device, a headphone or earpiece device, a device embedded in eyeglasses or other equipment worn on a user's head, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile."


Review Apple's patent application number 20210020140 for finer details. Considering that this is a patent application, the timing of such a product to market is unknown at this time.


Cancelling the Ghosting Phenomena


The second display centric patent 20210018795 that was published last Thursday by the U.S. Patent and Trademark Office is titled Display Backlighting Systems with Cancellation Architecture for Cancelling Ghosting Phenomena. It's more of a technical patent


Apple notes that a ghost effect or phenomena refers to the trailing of a moving object appearing on a display panel. Ghosting can happen even with static images for passive matrix drive. If there is a highlight in one row of LEDs, it can cause a ghosting to appear in the next row of LEDs. For LED displays, the ghosting phenomena may be caused by parasitic capacitance, which generates a ghost current spike and forces the time-multiplexed LEDs to emit a brief flash of light when the LEDs should have been turned off.


At a high level, ghost cancellation architectures of a 2D backlight passive matrix display driver is described that will perform ghost cancellation during transitions between different rows of LEDs in order to avoid unintended light coming out of LEDs that are intended to be OFF.


Parasitic capacitances can cause the unintended light. These ghost cancellation architectures discharge anodes of LEDs with a discharge voltage level and precharge cathodes of LEDs with a precharge voltage level. Based on the level of ghosting artifacts, either or both of pre-charge and discharge can be enabled.


While Apple's patent figure 1 illustrates an iPad, the invention could be applied to various Apple devices such as MacBooks, iPhones, Apple Watch, Head Mounted Devices, a Television (which Apple is mentioning more often in the last year), a gaming device, automobiles and more.


Review Apple's patent application 20210018795 for deeper technical points. Considering that this is a patent application, the timing of such a product to market is unknown at this time.


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