The below article contains excerpts from The Display Calibration Guide.
Introduction
Dynamic Image Processing is used to improve image quality and will work either alongside dynamic light control or independent of it. It is used in the following ways:
- To help improve contrast or the perception of contrast
- To maintain image integrity as dynamic dimming isemployed. This is normally by manipulating gamma tocounteract the dimming of brighter areas of the image.
- To maintain image integrity as the source content istranslated from one standard to another (we will talk about standards in the next chapter)
In addition, dynamic image processing can be done full-screen or using AI-assisted object-based image processing. Object- based dynamic processing – such as Sony’s Object-based remaster – looks at individual objects within the frame and will apply different processing to those elements – kind of like Photoshop – as opposed to simply manipulating gamma or colour for the whole image.
While dynamic image processing is helpful when playing back content, it is undesirable while doing calibration, so we generally turn these off where possible and then turn them back on when it is time to review our work.
Dynamic Gamma Manipulation
On displays where the backlight is controlled as one monolithic unit (whether it’s a projector’s light source or a TV’s backlight), the light source is dimmed the same everywhere on the screen. This means that highlights or bright areas of the image are also dimmed when trying to lower the black floor in darker scenes.
To combat this, some displays will manipulate the gamma so that bright areas will stay bright while dark areas can get darker. This way the display can create an even greater sense of contrast – while ensuing that artefacts from the dimming are reduced.
Some displays and video processors will allow you to run dynamic gamma manipulation as a way of improving contrast – with or without dimming. This is normally called contrast enhancer or something along those lines and can be implemented without dimming.
While Dynamic gamma manipulation can be effective, it can also introduce its own artefacts. It can result in both highlights and dark areas of the image getting too compressed, and losing detail. It can also result in colour desaturation if dynamic gamma is not used with the next dynamic technology we will talk about: Dynamic Colour Management.
Dynamic Colour Management
When a display’s light source changes in intensity – either because of dynamic dimming or – as in the case of HDR – because the display is unable to reach the correct brightness the standard requires, we may perceive colour shifts.
To combat this, a display can implement dynamic colour manipulation. Displays employing dynamic dimming may for example store the relative colour shifts that dynamic light source changes introduce – let it be lamp, dynamic iris, laser or backlight dimming. This way, the display can dynamically shift colour in a way that maintains the calibrated settings.
This is why JVC projectors need to be calibrated to different manual iris positions when doing auto-calibration, for example. Without this, the internal colour management tables controlling this dynamic action will not be updated correctly – and colour shifts will occur during dynamic iris movement.
Dynamic Tone Mapping
Tone Mapping is generally employed when tone mapping HDR content to be displayed on
- Displays with lower peak brightness than what is in thesource material.
- Displays with lower gamut / colour volume than the sourcematerial.
As we discussed earlier, both points apply to almost all commercially available displays as no display can reach either the full brightness or the full saturation required to display HDR in all its glory.
Dynamic Tone Mapping employs both dynamic gamma and dynamic colour management changes to enable the display to render the original source material faithfully on a much less capable display.
However, instead of applying a static tone map to the entire content, the content is analysed frame by frame, or scene by scene and will have its tone map adjusted to fit the content better to the display’s capability.
Dynamic Tone Mapping is generally executed by the display and can be driven entirely by the display’s algorithms, or as is the case with Dolby Vision and HDR10+, can be driven by meta-data embedded in the content itself. More on this last point when we get to HDR standards.
Object-Based Dynamic Processing
As chips get more and more powerful, they are able to dedicate more and more processing power to each frame of video.
This is why now it’s possible to employ AI to analyse each frame, identify the different objects within the frame, and apply different upscaling, gamma and colour manipulation on a per- object basis as opposed to the whole frame en masse. This can result in better quality image processing dependent on how well the AI has been trained and its neural networks.
Sony calls this Object-Based Remaster. But this is also employed by Samsung for its upscaling on their QLED TVs.
The Display Calibration Guide
If you would like to learn more about displays, and display calibration, you can get The Display calibration Guide here.
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