[ad_1]
//php echo do_shortcode(‘[responsivevoice_button voice=”US English Male” buttontext=”Listen to Post”]’) ?>
Cell phones have come a long way in the last few decades. From feature phones, which first appeared in the late 1990s with the development of mobile communications, to the smartphones that we know today, they are no longer merely a means of communicating via voice and text. Smartphones are now widely recognized as viable alternatives to heavy DSLR cameras due to their high-performance camera functionalities. This article will introduce the technologies that SK hynix has been developing to allow users to experience better smartphone cameras, with a particular focus on high dynamic range (HDR)1 technology.
1High dynamic range (HDR): In photography, dynamic range describes the range between the image’s brightest and darkest areas. HDR offers a greater contrast compared to the standard dynamic range (SDR) and broadens the brightness range to match what the human eye sees as closely as possible.
Efforts to Improve Dynamic Range Performance of Photography
In recent years, smartphone camera sensors have evolved in function and configuration, approaching the level of DSLR cameras. However, while DSLR cameras have a pixel size of 3-4 micrometers (μm) and 14-bit analog-to-digital converter (ADC) technology or higher, smartphone cameras have a pixel size of 1μm and a 10-bit ADC due to the physical constraints of smartphone size. As a result, smartphones continue to lag behind DSLRs in terms of low-light image quality and dynamic range performance, making the development of technologies to improve them a current trend in the CIS2 industry.
Dynamic range can be defined as the ratio of full well capacity (FWC)3 and temporal noise4 (TN); therefore, improving dynamic range performance can be accomplished by either increasing FWC or reducing TN through structural changes of pixels and circuit improvements. However, due to the technical difficulties of developing advanced pixels and circuitry, this approach is limited in its ability to apply to a wide range of smartphones at different price points.
2CMOS image sensor (CIS): A sensor that converts the color and intensity of light into an electrical signal before relaying it to a processing unit. It essentially acts as the “eyes” of digital devices such as smartphones and tablets.
3Full well capacity (FWC): This denotes the maximum charge a pixel can hold without saturation beyond which the signal quality deteriorates. When the charge in a pixel exceeds the saturation level, the charge may overflow into adjacent pixels in an effect called “blooming.”
4Temporal noise (TN): Undesired variations of image brightness and color resulting from fluctuations in generating a digital value from a single pixel by converting incoming photons into electrons.
This is why SK hynix has focused on implementing HDR technology by improving dynamic range through the addition of ISP5 hardware logic while maintaining the existing pixel structure and 10-bit ADC. This evolution in technology ensures a wider audience can experience HDR capabilities, at all smartphone price points.
5Image signal processor (ISP): An ISP is a type of media processor mainly responsible for image processing in digital cameras and mobile phones. It converts an image into its digital equivalent and conducts operations such as noise reduction, auto exposure, autofocus, auto white balance, HDR correction, and image sharpening.
Evolution of SK hynix’s HDR Technology Development: From QHDR to DAG & iDCG HDR
SK hynix’s HDR technology has advanced significantly since its development of quad HDR (QHDR) in 2017.
QHDR (Developed in 2017)
QHDR, also known as quad-sensor HDR, uses multiple exposure time-based HDR technology that expands the dynamic range using single-frame images with exposure times patterned to the quad color filter array (CFA)6. As quad CFA technology advanced, HDR capabilities were integrated into the sensor to enhance the competitiveness of high-resolution sensors, resulting in the development of QHDR. This sensor also offers support for intellectual properties (IP)7 such as fusion and tone mapping processes.
6Color filter array (CFA): A matrix of tiny color filters placed over the pixel sensors of an image sensor to capture color information (R/G/B). Recently, a series of high-quality and high-functional CIS products have been released thanks to the development of various application technologies such as Bayer and Quad being combined with the basic form of CFA.
7Intellectual property (IP): In this context, IP refers to a reusable block of functionality which can be used as a hardware core/library or software library.
sHDR (Developed in 2018)
QHDR implements HDR technology solely through the sensor, requiring significant hardware resources within the sensor itself. Staggered HDR (sHDR), on the other hand, optimizes image quality and expands the dynamic range by collaborating between the sensor and the application processor (AP), which are both intrinsically connected within the camera’s interface.
With sHDR technology, the sensor outputs multi-frame images with different exposure times and transmits them to the AP. The AP then applies ISP processing for HDR, encompassing functions like fusion and tone mapping. In this case, the sensor requires high-speed transmission of multiple images with multiple exposure times.
iDCG-HDR (Developed 2021-2022)
Since existing sHDR and QHDR technologies are based on multiple exposure times, this inevitably leads to motion artifacts8 when adjusting exposure durations. Recognizing these constraints, SK hynix developed intra-scene dual conversion gain (iDCG)-HDR technology.
8Motion artifacts: Also known as “ghosting artifacts”, these image disturbances are caused by camera shake and/or object motion during the fusion of multiple differently exposed images.
DCG is an innovative technology that can change the volume of the output signal by toggling the DCG capacitance on the floating node (FN), even if the same amount of light is received. By merging high conversion gain (HCG) and low conversion gain (LCG) images—both captured during a single exposure but with different brightness—iDCG-HDR expands the dynamic range to achieve HDR.
The sensor supports fusion ISP to combine images from two frames, resulting in a DR boost of roughly 12 decibels (dB) at a DCG ratio of 1:4.
DAG-HDR (Developed in 2023)
While iDCG-HDR minimizes motion artifacts better than QHDR and sHDR, it is constrained by using physically fixed conversion gain (CG)9. This limits its ability to flexibly improve dynamic range across a variety of shooting conditions. It also has the disadvantage of higher manufacturing costs due to the addition of transistors to control the CG.
In contrast, dual analog gain (DAG)-HDR achieves the effect of HDR from two frames captured with two different analog gains (AG)10 within a defined time. Although its maximum dynamic range is less than that of iDCG-HDR, DAG-HDR offers the flexibility to adjust the dynamic range as needed and realize the HDR effect even on low-end smartphones.
9Conversion gain (CG): A ratio of output signal level to the input signal level. This is one of the most fundamental characteristics of the image sensors to guarantee quantitative correspondence between input and output images.
10Analog gain (AG): It increases the analog signal before it is transformed into a digital signal (A/D-Conversion). It offers higher sensitivity and less noise over solely relying on digital gain.
DAG & iDCG HDR (Developed in 2023)
This HDR technology based on a single exposure time combines DAG and iDCG to minimize motion artifacts while flexibly improving the dynamic range within the user’s various shooting conditions. In other words, it integrates the fluid dynamic range adjustability of DAG-HDR with the significant dynamic range enhancements offered by iDCG-HDR. With a CG ratio of 1:4 and an AG of 16x, the dynamic range of the combined DAG & iDCG HDR can improve by up to 36 dB.
Looking ahead, SK hynix will concentrate on single exposure time-based DAG & iDCG HDR technology that minimizes motion artifacts while flexibly improving dynamic range under a variety of shooting conditions. This commitment underscores SK hynix’s dedication to ensuring all smartphone users can truly experience the full potential of HDR with a maximum dynamic range.
[ad_2]
Source link