24,282 research outputs found
Algorithms for compression of high dynamic range images and video
The recent advances in sensor and display technologies have brought upon the High Dynamic Range (HDR) imaging capability. The modern multiple exposure HDR sensors can achieve the dynamic range of 100-120 dB and LED and OLED display devices have contrast ratios of 10^5:1 to 10^6:1.
Despite the above advances in technology the image/video compression algorithms and associated hardware are yet based on Standard Dynamic Range (SDR) technology, i.e. they operate within an effective dynamic range of up to 70 dB for 8 bit gamma corrected images. Further the existing infrastructure for content distribution is also designed for SDR, which creates interoperability problems with true HDR capture and display equipment.
The current solutions for the above problem include tone mapping the HDR content to fit SDR. However this approach leads to image quality associated problems, when strong dynamic range compression is applied. Even though some HDR-only solutions have been proposed in literature, they are not interoperable with current SDR infrastructure and are thus typically used in closed systems.
Given the above observations a research gap was identified in the need for efficient algorithms for the compression of still images and video, which are capable of storing full dynamic range and colour gamut of HDR images and at the same time backward compatible with existing SDR infrastructure. To improve the usability of SDR content it is vital that any such algorithms should accommodate different tone mapping operators, including those that are spatially non-uniform.
In the course of the research presented in this thesis a novel two layer CODEC architecture is introduced for both HDR image and video coding. Further a universal and computationally efficient approximation of the tone mapping operator is developed and presented. It is shown that the use of perceptually uniform colourspaces for internal representation of pixel data enables improved compression efficiency of the algorithms. Further proposed novel approaches to the compression of metadata for the tone mapping operator is shown to improve compression performance for low bitrate video content. Multiple compression algorithms are designed, implemented and compared and quality-complexity trade-offs are identified. Finally practical aspects of implementing the developed algorithms are explored by automating the design space exploration flow and integrating the high level systems design framework with domain specific tools for synthesis and simulation of multiprocessor systems. The directions for further work are also presented
High Dynamic Range Imaging Technology.
Abstract:
In this lecture note, we describe high dynamic range (HDR) imaging systems. Such systems are able to represent luminances of much larger brightness and, typically, a larger range of colors than conventional standard dynamic range (SDR) imaging systems. The larger luminance range greatly improves the overall quality of visual content, making it appear much more realistic and appealing to observers. HDR is one of the key technologies in the future imaging pipeline, which will change the way the digital visual content is represented and manipulated today
Objective and subjective assessment of perceptual factors in HDR content processing
The development of the display and camera technology makes high dynamic range (HDR) image become more and more popular. High dynamic range image give us pleasant image which has more details that makes high dynamic range image has good quality. This paper shows us the some important techniques in HDR images. And it also presents the work the author did. The paper is formed of three parts. The first part is an introduction of HDR image. From this part we can know why HDR image has good quality
Põhjalik uuring ülisuure dünaamilise ulatusega piltide toonivastendamisest koos subjektiivsete testidega
A high dynamic range (HDR) image has a very wide range of luminance levels that
traditional low dynamic range (LDR) displays cannot visualize. For this reason, HDR
images are usually transformed to 8-bit representations, so that the alpha channel for
each pixel is used as an exponent value, sometimes referred to as exponential notation
[43]. Tone mapping operators (TMOs) are used to transform high dynamic range to
low dynamic range domain by compressing pixels so that traditional LDR display can
visualize them. The purpose of this thesis is to identify and analyse differences and
similarities between the wide range of tone mapping operators that are available in the
literature. Each TMO has been analyzed using subjective studies considering different
conditions, which include environment, luminance, and colour. Also, several inverse
tone mapping operators, HDR mappings with exposure fusion, histogram adjustment,
and retinex have been analysed in this study. 19 different TMOs have been examined
using a variety of HDR images. Mean opinion score (MOS) is calculated on those selected
TMOs by asking the opinion of 25 independent people considering candidates’
age, vision, and colour blindness
Digital Color Imaging
This paper surveys current technology and research in the area of digital
color imaging. In order to establish the background and lay down terminology,
fundamental concepts of color perception and measurement are first presented
us-ing vector-space notation and terminology. Present-day color recording and
reproduction systems are reviewed along with the common mathematical models
used for representing these devices. Algorithms for processing color images for
display and communication are surveyed, and a forecast of research trends is
attempted. An extensive bibliography is provided
A simplified HDR image processing pipeline for digital photography
High Dynamic Range (HDR) imaging has revolutionized the digital imaging. It allows
capture, storage, manipulation, and display of full dynamic range of the captured scene.
As a result, it has spawned whole new possibilities for digital photography, from photorealistic
to hyper-real. With all these advantages, the technique is expected to replace
the conventional 8-bit Low Dynamic Range (LDR) imaging in the future. However,
HDR results in an even more complex imaging pipeline including new techniques for
capturing, encoding, and displaying images. The goal of this thesis is to bridge the
gap between conventional imaging pipeline to the HDR’s in as simple a way as possible.
We make three contributions. First we show that a simple extension of gamma
encoding suffices as a representation to store HDR images. Second, gamma as a control
for image contrast can be ‘optimally’ tuned on a per image basis. Lastly, we show
a general tone curve, with detail preservation, suffices to tone map an image (there is
only a limited need for the expensive spatially varying tone mappers). All three of our
contributions are evaluated psychophysically. Together they support our general thesis
that an HDR workflow, similar to that already used in photography, might be used. This
said, we believe the adoption of HDR into photography is, perhaps, less difficult than it
is sometimes posed to be
Methods for Improving the Tone Mapping for Backward Compatible High Dynamic Range Image and Video Coding
International audienceBackward compatibility for high dynamic range image and video compression forms one of the essential requirements in the transition phase from low dynamic range (LDR) displays to high dynamic range (HDR) displays. In a recent work [1], the problems of tone mapping and HDR video coding are originally fused together in the same mathematical framework, and an optimized solution for tone mapping is achieved in terms of the mean square error (MSE) of the logarithm of luminance values. In this paper, we improve this pioneer study in three aspects by considering its three shortcomings. First, the proposed method [1] works over the logarithms of luminance values which are not uniform with respect to Human Visual System (HVS) sensitivity. We propose to use the perceptually uniform luminance values as an alternative for the optimization of tone mapping curve. Second, the proposed method [1] does not take the quality of the resulting tone mapped images into account during the formulation in contrary to the main goal of tone mapping research. We include the LDR image quality as a constraint to the optimization problem and develop a generic methodology to compromise the trade-off between HDR and LDR image qualities for coding. Third, the proposed method [1] simply applies a low-pass filter to the generated tone curves for video frames to avoid flickering during the adaptation of the method to the video. We instead include an HVS based flickering constraint to the optimization and derive a methodology to compromise the trade-off between the rate-distortion performance and flickering distortion. The superiority of the proposed methodologies is verified with experiments on HDR images and video sequences
Advances on CMOS image sensors
This paper offers an introduction to the technological advances of image sensors designed using
complementary metal–oxide–semiconductor (CMOS) processes along the last decades. We review
some of those technological advances and examine potential disruptive growth directions for CMOS
image sensors and proposed ways to achieve them. Those advances include breakthroughs on
image quality such as resolution, capture speed, light sensitivity and color detection and advances on
the computational imaging. The current trend is to push the innovation efforts even further as the
market requires higher resolution, higher speed, lower power consumption and, mainly, lower cost
sensors. Although CMOS image sensors are currently used in several different applications from
consumer to defense to medical diagnosis, product differentiation is becoming both a requirement and
a difficult goal for any image sensor manufacturer. The unique properties of CMOS process allows the
integration of several signal processing techniques and are driving the impressive advancement of the
computational imaging. With this paper, we offer a very comprehensive review of methods,
techniques, designs and fabrication of CMOS image sensors that have impacted or might will impact
the images sensor applications and markets
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