Not long ago, we talked about Disruptive trends shaping the display solutions of the future and how High Dynamic Range (HDR) is something of a game changer, promising higher-fidelity viewing, preserved highlights and texture, and visuals that more closely reflect the human visual experience.
Well, it’s time to pop the corks and unfurl the streamers – Arm Assertive Display 5 is here, and it brings with it a complete set of HDR management features for display pipelines!
Assertive Display has long been heralded as the market-leading outdoor viewability solution and, to date, has been shipped in over 1 billion mobile devices. Powered by an innovative local tone-mapping engine, it continuously adapts each individual pixel to compensate for sub-optimal conditions – such as limitations of the display, ambient light conditions and reduced backlight – to maintain a high-quality viewing experience, whether indoors or outside in bright sunshine.
Historically, display technologies have struggled to replicate what the human eye sees: traditional Standard Dynamic Range (SDR) content, such as sRGB, has a contrast ratio around 2,000:1 which means that, onscreen, shadow can become a dark mass, and the texture of light areas – such as cloud – tends to be bleached out.
HDR content, however, can achieve contrast ratios around 100,000:1, making colors seem richer, details more vivid and textures more authentic, providing a viewing experience that’s breathtakingly lifelike … if those contrast ratios can be accurately reproduced.
Of course, in an ideal world, we’d all be watching HDR content on a top-end HDR panel in a darkened room to preserve the nuances of light and shade and conserve that superlative HDR image quality. Unfortunately, most of us wantonly watch our movies in a range of non-ideal viewing conditions – and the majority of screens available on the consumer market are unable to display the full dynamic range of HDR content anyway.
There is, however, a solution…
Whether we’re watching on a mobile phone or a state-of-the-art HDR panel, we take it for granted that our content will be more-or-less faithfully reproduced at the touch of button. Yet the pipeline for getting those images to your screen is relatively long and convoluted.
First, the digital image is captured, before being efficiently compressed and encoded for transmission to your device. Tone mapping is then used – either to accommodate HDR content to lower spec displays or to ‘upgrade’ the content for display on HDR devices, as well as dynamically compensating for ambient lighting conditions. Finally, the images are displayed on the target device.
Assertive Display 5’s HDR management feature gives control of every stage of the display pipeline journey, enabling optimal performance – along with significant power-saving:
Assertive Display 5 utilizes iridix8 HDR, an advanced and high-precision local tone-mapping engine to achieve a superb HDR experience, even on an SDR panel.
Tone mapping essentially maps one set of colors to another, approximating the appearance of high dynamic range images on devices with a more limited dynamic range.
Global, or spatially uniform, tone mapping establishes an average transfer curve, and uses that to map every pixel within the image in the same way. Although it’s fast and simple to implement, it can result in a loss of highlights, contrast, saturation and a shift in the color and skin tone.
Local, or spatially variable, tone mapping uses more complicated algorithms, calculating individual transfer curves for each pixel in accordance with the local features of the image, preserving highlights, color and contrast, and revealing the detail within darker areas. Since human vision is extremely sensitive to local contrast, it creates a more realistic image that’s rich in detail and which the eye accepts as a close reflection of the human visual experience.
HDR content is also notoriously vulnerable to sunlight; while ambient light and reflections can cause the panel to lose contrast and detail, Assertive Display’s tone mapping dynamically compensates, ensuring an all-round high-quality HDR viewing experience – irrespective of environmental illumination.
HDR content typically has a wider color gamut than traditional content formats: SDR uses Rec.709 color space, while HDR uses Rec.2020’s wide color gamut, or WCG.
Where HDR increases the dynamic range of an image, WCG increases the available palette: with more shades of each color, chromatic intensity is increased, providing a richer, more lifelike viewing experience.
Although today’s HDR displays are not yet capable of showing the full gamut of Rec.2020, they are able to achieve the P3 gamut, which sits between the capabilities of Rec.709 and Rec.2020 – and performance is improving all the time. However, as we’ve already mentioned, irrespective of the panel’s properties, the gamut of the content must be properly mapped to the gamut of the display in order to achieve the most authentic color experience.
Three-dimensional look-up tables (3D LUT) provide an efficient solution, mapping color channels independently to preserve the textures of the wider gamut, but are typically costly on silicon. However, Assertive Display 5 utilizes a novel, compact and silicon-friendly hardware implementation of 3D LUT to perform advanced gamut and color mapping, preserving subtle gradations of color and maintaining the integrity of the viewing experience.
We’ve already looked at how Assertive Display’s tone mapping dynamically compensates for ambient light and reflection to deliver a high-quality HDR viewing experience irrespective of environmental illumination, but what’s pretty amazing is that it does this while offering significant display power-saving features.
Conventional content-adaptive power-saving approaches can wash out highlights and have easily noticeable temporal artefacts, but Assertive Display’s content-adaptive backlight control solution works in conjunction with the iridix local tone-mapping engine to achieve seamless dynamic backlight behavior, without introducing clipping artifacts – even at reduced backlight levels.
Whilst we’re all quite used to split-screen views on our laptop, the composition of multiple windows – including freeform, resized windows and Picture-in-Picture – is fast becoming a ‘thing’ across a range of devices, with premium display solutions capable of compositing four windows or more.
Assertive Display 5, integrated with Mali D71, supports the handling of both HDR and SDR windows within the same composition scene, allowing multiple windows to be scaled simultaneously.
Assertive Display 5 achieves the advanced features of HDR management, outdoor viewability and power-saving at a particularly small die size and a simple RGB interface, making it easy to integrate and utilize.