High Dynamic Range Displays

Transcription

1 High Dynamic Range Displays Dave Schnuelle Senior Director, Image Technology Dolby Laboratories The Demise of the CRT What was good: Large viewing angle High contrast Consistent EO transfer function Good motion rendition 50+ years of experience What was bad: Poor ambient contrast Low light output capability Short life span Spot size MTF roll-off LCD corollary: Challenge Challenge Requires standard Improving 5 years of experience Good ambient contrast High light output Long life span High MTF fixed pixel These differences are what get us in trouble today 1

2 Our World and the Human Visual System Logarithmic Luminance in cd/m 2 1.E-06 1.E-04 1.E-02 1.E+00 1.E+02 1.E+04 1.E+06 1.E+08 Simultaneous HVS Range Adaptation Range Displays Display Technology Conventional Display Cold cathode fluorescents (CCFL) provide LCD backlight Light spread evenly and does not vary with image content Image control is purely in the LCD panel, not the backlight, and is limited to 8-bit signal to Red, Green, and Blue colour channels 2

3 Display Technology HDR Display LCD backlight is provided by an array of LED s Each LED is controlled with 8 bit (255 step) signal Brightness is adjusted to level demanded by source image LCD panel provides additional 8 bits of brightness control LED and LCD panel combine optically to deliver 16 bit performance LED s provide greater brightness while saving power Blur Correction Algorithm Image Processing HDR Image LED array LCD with correction Output image 3

4 HDR Display Technology Veiling Luminance Receive Image Drive LED Divide Image by LED light field to obtain LCD values Output Luminance is the product of LED light field and LCD transmission (modest error) HDR Display Technology Veiling Luminance Receive Image Drive LED Divide Image by LED light field to obtain LCD values Output Luminance is the product of LED light field and LCD transmission (Problematic error) 4

5 HDR Display Technology Veiling Luminance The impact on the human visual system of bright objects on nearby dark areas can be calculated dark area L1 L2 B L1 your eye A a b c P( α )= ηδ ( α) + f( α) bright object HDR Display Technology Veiling Luminance Veiling Luminance masks imperfection 5

6 HDR Display Technology High resolution Colour Image Dual Modulation High Dynamic Low resolution Range Display Luminance Modulated Second Image High/Low Resolution and Correction Veiling Luminance Calibration Techniques Factory calibration for luminance uniformity Primarily affected by LED manufacturing differences Stored reference model Active internal calibration during use Primarily affected by LED differential aging Comparison to stored reference model Manual calibration with external instrument Set white point Emulate another display 6

7 Factory Calibration Luminance Uniformity Results Uncalibrated 46 HDR display showing medium grey image Calibrated 46 HDR display showing medium grey image Internal Calibration Software Correction for dim LEDs (extreme case) 7

8 Internal Calibration Luminance Uniformity before and after software correction Lifetime Testing Process 50mm diameter Integrating Sphere for LED lifetime test 8

9 Response Uncontrolled Response VS Gain Relative Luminance [1] uncontrolled controlled Relative to Initial uncontrolled response gain equivalent time [hr] [Hoursx10] equivalent time [hr] [Hoursx10] Response (with Error Bars) Error Relative to Initial Luminance Luminance of PSF Peak [nits] controlled response [%] error equivalent time [hr] [Hoursx10] equivalent time [hr] [Hoursx10] HDR Display luminance characterization 9

10 HDR Display luminance characterization 10

11 Color Gamut Study Rec 709 SMPTE P3 Test of actual RGB LEDs showing Gamut larger than SMPTE P3 11

12 HDR Display Technology Summary High resolution Colour Image Dual Modulation High Dynamic Low resolution Range Display Luminance Modulated Second Image High/Low Resolution and Correction Veiling Luminance 12