WO2009042036A2 - Preferential tone scale for electronic displays - Google Patents
Preferential tone scale for electronic displays Download PDFInfo
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- WO2009042036A2 WO2009042036A2 PCT/US2008/010659 US2008010659W WO2009042036A2 WO 2009042036 A2 WO2009042036 A2 WO 2009042036A2 US 2008010659 W US2008010659 W US 2008010659W WO 2009042036 A2 WO2009042036 A2 WO 2009042036A2
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- luminance
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- 238000013507 mapping Methods 0.000 claims abstract description 58
- 238000000034 method Methods 0.000 claims abstract description 36
- 230000009466 transformation Effects 0.000 claims abstract description 14
- 230000000007 visual effect Effects 0.000 claims abstract description 10
- 235000019557 luminance Nutrition 0.000 claims description 105
- 238000002310 reflectometry Methods 0.000 claims description 9
- 238000012545 processing Methods 0.000 claims description 3
- 230000033458 reproduction Effects 0.000 description 35
- 239000003086 colorant Substances 0.000 description 10
- 238000005286 illumination Methods 0.000 description 6
- 238000010586 diagram Methods 0.000 description 4
- 238000000844 transformation Methods 0.000 description 3
- 239000000654 additive Substances 0.000 description 2
- 230000000996 additive effect Effects 0.000 description 2
- 238000012937 correction Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 239000006117 anti-reflective coating Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000003384 imaging method Methods 0.000 description 1
- 239000004973 liquid crystal related substance Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 230000001131 transforming effect Effects 0.000 description 1
Classifications
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- G06T5/92—
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/46—Colour picture communication systems
- H04N1/56—Processing of colour picture signals
- H04N1/60—Colour correction or control
- H04N1/6027—Correction or control of colour gradation or colour contrast
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T2207/00—Indexing scheme for image analysis or image enhancement
- G06T2207/10—Image acquisition modality
- G06T2207/10016—Video; Image sequence
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T2207/00—Indexing scheme for image analysis or image enhancement
- G06T2207/20—Special algorithmic details
- G06T2207/20004—Adaptive image processing
- G06T2207/20012—Locally adaptive
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2340/00—Aspects of display data processing
- G09G2340/06—Colour space transformation
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G5/00—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators
- G09G5/02—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators characterised by the way in which colour is displayed
Definitions
- the present invention relates to tone reproduction in electronic displays.
- Additive color digital image display devices are well known and are based upon a variety of technologies such as cathode ray tubes, liquid crystal modulators, and solid-state light emitters such as Organic Light Emitting Diodes (OLEDs).
- OLEDs Organic Light Emitting Diodes
- a pixel includes red, green, and blue colored OLEDs. These OLEDs are color primaries that define a color gamut. By additively combining the illumination from each of these three OLEDs, i.e. with the integrative capabilities of the human visual system, a wide variety of colors can be achieved. However, it is not enough to simply provide an image. Displays are intended to provide a realistic representation of the images to the viewer, and there can be a need to correct display tonal responses to enhance the display image quality.
- the tonal enhancement must be implemented in the display's imaging chain.
- the relationship between the reproduced luminances of objects in an image scene reproduction compared to the original scene luminances of those objects is a critical aspect of achieving viewer satisfaction with the reproduction.
- the theoretically correct reproduction for this purpose is a one-to-one relationship between the luminances of the original scene and the luminances of the reproduction only if the conditions under which the reproduction is viewed are identical to the conditions under which the original scene was viewed. This is described in the book "The Reproduction of Colour” by Dr. R.W.G. Hunt, (Fountain Press, England— Fourth Ed.), specifically in Chapter 6 wherein the fundamentals of tone reproduction are discussed.
- the conditions under which an original scene or a display showing a reproduction of a scene are viewed can be characterized by a number of parameters, including illuminance on the scene or the display and surrounding illumination. Viewing conditions are typically further characterized by parameters of the major sources illuminating the scene or display. These include position of the sources, their chromaticity and illuminance, and their emission patterns (for example, specular or diffuse).
- One useful way of summarizing some of these parameters is by characterizing viewing flare: the amount of illumination not generated by a display which the user sees while viewing the display. This can include light reflected off the display from sources in the viewing environment, and light internally reflected within the display (i.e. optical crosstalk).
- tone-reproduction standard is sRGB, described in IEC 61966-2.1 :1999 + A 1.2003 Multimedia systems and equipment — Colour measurement and management — Part 2-1 : Colour management — Default RGB colour space — sRGB, Version 1.10, November 5, 1996.
- This standard attempts to account for the viewing conditions of a typical office environment. This is shown as system tonescale curve 170a in FIG. 3. This curve covers a reproduced luminance dynamic range of 3.5 decades over a three-decade range of scene luminance, which is typical for a CRT display.
- OLED displays provide a greater dynamic range that has not been used in previous tone-mapping methods such as sRGB. It is desirable, therefore, to provide an image reproduction system and method that offers an overall tone mapping in the reproduced image, as seen by the viewer, that is perceived to be a natural reproduction of the original scene while utilizing the full display dynamic range.
- This object is achieved by a method of displaying on a display a visual reproduction of an original scene with a preferential tone mapping; said display having a selected display white point and a selected display black point separated by more than 3.5 decades of luminance; the method comprising the steps of capturing original scene parameters, performing a transformation on said captured scene parameters, and displaying a visual reproduction of the scene on the display from the transformed captured scene parameters; wherein said transformation, taken in conjunction with untransformed characteristics of the capturing and displaying steps, results in a reproduced tone mapping having: a. a dynamic range greater than 3.5 decades; b.
- FIG. 1 shows a set of display system tonescale curves according to this invention, which account for different viewing environments
- FIG. 2 shows the first derivative of the curves of FIG. 1
- FIG. 3 shows one of the curves of FIG. 1 in comparison with prior- art system tonescale curves
- FIG. 4 shows the first derivative of the curves of FIG. 3;
- FIG. 5 shows one of the curves of FIG. 1 in comparison with modified prior-art system tonescale curves
- FIG. 6 shows the first derivative of the curves of FIG. 5
- FIG. 7 shows one of the curves of FIG. 1 in comparison with some existing displays
- FIG. 8 shows the first derivative of the curves of FIG. 7
- FIG. 9 shows a schematic diagram of an image capture and display process wherein this invention is applicable.
- FIG. 10 shows a four-quadrant tone reproduction diagram as used in accordance with this invention. DETAILED DESCRIPTION OF THE INVENTION
- FIG. 1 shows a set of display system tonescale curves according to this invention, which are designed for different viewing conditions.
- FIG. 2 shows the first derivatives of the curves of FIG. 1.
- the abscissa of the system tonescale curve is the base- 10 logarithm of the scene luminance relative to a 100% diffuse reflector in the original scene.
- the ordinate of the system tonescale curve is the negative base- 10 logarithm of the reproduced luminance relative to the display white point 15.
- FIGs. 1 and 2 show the preferential tone mapping for reproduction of an original scene on a display that has a selected display white point 15 and selected display black point 10 that are separated by more than 3.5 decades, or orders of magnitude, of reproduced (display) luminance.
- the display can be an OLED, LCD, or plasma display.
- An OLED display in particular can have a reproduced luminance dynamic range of four decades or orders of magnitude.
- the system tonescale has a dynamic range of greater than 3.5 decades for reproduced luminance from black point 10 to white point 15. This allows the tonescale to take full advantage of the dynamic range of the display.
- system tonescale curves 110a, 120a, 130a, 140a, and 150a are some representative embodiments of reproduced tone mapping in accordance with this invention. They represent an envisioned range of tone mapping curves for a display under different conditions to be described herein. Such conditions can include variations in the amount of light in the viewing environment, characteristics of the display such as surface reflectivity, and characteristics of the scene to be displayed, such as the luminance range of the scene.
- the different curves include different levels of flare correction and different slope characteristics, and the optimum curve to use for a display depends upon the conditions.
- System tonescale curve 130a can be a preferential tone mapping for a dark room in which there is relatively little viewing flare.
- System tonescale curve 110a can be a preferential tone mapping in the presence of some viewing flare, e.g. a living room with average lighting.
- System tonescale curve 140a can be a preferential tone mapping when the viewing flare is very great, e.g. a brightly lit showroom.
- FIG. 2 shows first derivative curves and restrictions on the first derivative of the reproduced tone mapping.
- the curves are the first derivative of the similarly numbered curve in FIG. 1 , e.g. first derivative curve 110b is the first derivative of system tonescale curve 110a, etc.
- first derivative curve 110b is the first derivative of system tonescale curve 110a, etc.
- the value of the first derivative of minus log reproduced display luminance (the vertical axis of FIG. 2) relative to log original scene luminance (the horizontal axis) is between -1.1 and -1.51, inclusive (shown by the vertical extent of limit 20) and desirably between -1.21 and -1.27, inclusive.
- This restriction allows good detail in highlights and light colors while not sacrificing the display's dynamic range.
- the first derivative value is less than or equal to -1.9 and greater than —4.0, (shown by the vertical extent of limit 40).
- the first derivative value is between -1.5 and -3.0, inclusive (shown by the vertical extent of limit 50).
- the first derivative preferably should have a value greater than -4.0 for all log scene luminances. For log scene luminances less than -2.0 and log scene luminances greater than -1.5, the first derivative value preferably should be greater than -3.0. This puts a limit on the allowable contrast of the display in this region, which increases the detail in reproduced dimly-lit images. Images with mid-scale to dark colors, like dark skin tones, will also have increased detail making them a more pleasing reproduction of the original scene.
- the first derivative further preferably should have a value greater than -0.5 for log scene luminances less than -2.8, as shown in FIG. 2. This will assure good shadow detail.
- the first derivative of the reproduced tone mapping preferably should be continuous for log scene luminances greater than -3 and less than zero, as shown in FIG. 2. This will prevent objectionable contouring due to instantaneous slope changes.
- the first derivative value for a log scene luminance of -2.0 is greater than that for a log scene luminance of -1.9, as shown in FIG. 2 by curves 110b, 120b, and 140b. This causes the system tonescale curve (FIG. 1) to be rounded at the top, and prevents excess low-end contrast, which is visually objectionable.
- the second derivative of the reproduced tone mapping is continuous for log scene luminances greater than -3 and less than zero. This will reduce the likelihood of objectionable contouring in extreme cases. This condition is fulfilled by the derivatives of curves 110b, 130b, and 150b of FIG. 2. It is further desirable that the reproduced tone mapping have a first derivative value for a log scene luminance of zero greater than the value for a log scene luminance of 0.6. This increases detail information in the scene highlights.
- the reproduced tone mapping to be used under a given set of conditions can be selected based on several criteria.
- One of the criteria can be the characteristics of the viewing environment, which can include factors such as surrounding illumination, viewing flare, surrounding illumination color, or illumination type (e.g. specular or diffuse).
- Another of the criteria can be the characteristics of the display, which can include factors such as display reflectivity and polarization.
- Another factor, ambient contrast ratio is a characteristic of both the environment and the display.
- flare can come from ambient light in the viewing environment, or light reflected from the face of the display, or both.
- the selection of reproduced tone mapping can provide pleasing images in the presence of flare.
- a tone mapping should be selected that compensates for flare, e.g. system tonescale curve 140a, which has a first derivative minimum at a higher log scene luminance, e.g. about -1.5 as shown by curve 140b in FIG. 2.
- a tone mapping with less compensation for flare should be selected, e.g. system tonescale curve 110a or 130a.
- the log scene luminances of the first derivative minimums for all of the curves of FIG. 2 are shown in Table 1, below.
- Such curves 110a and 130a have a first derivative minimum at a relatively lower scene luminance in comparison to that of curve 140a, e.g. log scene luminance of about -1.7 for curve 110b, or about -2.1 for curve 130b.
- the reproduced tone mapping to be used is selected based on the characteristics of the viewing environment, one would select a reproduced tone mapping with a first derivative minimum at a relatively higher scene luminance, e.g. system tonescale curve 140a, when the display is viewed in the presence of a relatively greater amount of ambient light falling on the face of the display; and one would select a reproduced tone mapping with a first derivative minimum at a relatively lower scene luminance, e.g. system tonescale curve 110a or 130a, when the display is viewed in the presence of a relatively lesser amount of ambient light falling on the display.
- the exact preferred curve to select will depend upon a combination of the viewing conditions and the properties of the display, including the surface reflectivity, and can be determined by those skilled in the art.
- the surface reflectivity of the display is determined by the display's construction. Many techniques for lowering surface reflectivity are known in the art, including circular polarizers, black matrix, and anti-reflective coatings.
- the reproduced tone mapping to use for the display can also be selected based on characteristics of the original scene to be displayed. Such characteristics can include scene luminance variation, highlight levels, and average luminance of the scene. For example, a scene in fog will have a small scene luminance variation and can look flat to the viewer. This can be adjusted to provide a more pleasing image to the viewer by selecting a curve with a different first derivative at a log scene luminance of -0.4.
- a reproduced tone mapping with a relatively more negative first derivative at log scene luminance -0.4 that is, the contrast of the system tonescale curve of FIG. 1 is greater at log scene luminance -0.4
- a reproduced tone mapping can be selected such that it has a first derivative with a relatively less negative value at log scene luminance -0.4.
- the value of the first derivative curves of FIG. 2 at log scene luminance -0.4 is shown in Table 1 , below. Curves need not be selected solely on the basis of first-derivative value at -0.4; other limits as specified herein, e.g. that at a log scene luminance of -0.6, may be regarded.
- a higher-contrast tone mapping is required for viewer satisfaction. This finding is surprising and contrary to published literature.
- the above contrast adjustment can be used in this situation.
- a reproduced tone mapping can be selected such that its first derivative has a relatively more negative value at a log scene luminance -0.4.
- a reproduced tone mapping can be selected such that its first derivative has a relatively less negative value at log scene luminance -0.4 when the display is viewed with a relatively lower amount of ambient light falling on its face.
- FIG. 3 shows one of the curves of FIG. 1 in comparison with prior- art system tonescale curves
- FIG. 4 shows the first derivative of the curves of FIG. 3.
- Curve 160a is taught as a system tonescale for self-illuminated displays by Buhr et al. in US 5,447,811, US 5,528,339, and references therein
- curve 160b of FIG. 4 is its first derivative.
- its dynamic range of 3.2 decades is insufficient for OLED displays. It also does not meet some of the requirements in FIG. 4, in particular the first derivative values at log scene luminance -1.9 and -2.0.
- Curve 170a the sRGB standard display curve
- curve 170b of FIG. 4 is its first derivative.
- Curve 170a does have a dynamic range of 3.5 decades, but was defined as nearly a straight line.
- the first derivative curve 170b does not meet the requirements of FIG. 4 at log scene luminance -1.9 and -2.0.
- the first derivative curve also has a significantly negative value at log scene luminance -3, which may lead to reproductions perceived as having excess low-end contrast.
- FIG. 5 shows one of the curves of FIG. 1 in comparison with modified prior-art system tonescale curves
- FIG. 6 shows the first derivative of the curves of FIG. 5.
- Curve 165a is the tonescale of Buhr et al. (Curve 160a in FIG. 3) that has been stretched to a dynamic range of 4 decades by use of a multiplier
- curve 165b is its first derivative. Although it has the required dynamic range, it does not meet many of the requirements in FIG. 6, in particular the first derivative values at log scene luminance -0.6, —1.9, and -2.0.
- Images having tonescales represented by curve 165a would have a compressed dynamic range, darker reproduced colors, and less detail information, especially in the midscale, than reproduced images having tonescales like curve 110a.
- Curve 175a is the sRGB standard display curve (Curve 170a in FIG. 3) that has been stretched to a dynamic range of 4 decades by use of a multiplier, and curve 175b is its first derivative. Curve 175a does have a dynamic range greater than 3.5 decades, but was defined as nearly a straight line. It does not meet the requirements of FIG. 6 at log scene luminance -1.9 and -2.0. The first derivative curve also has a value less than -0.5 at log scene luminance -3. Images having tonescales represented by curve 175a would look flat and have lifted (i.e. lighter) mid to dark tones relative to images having tonescales defined by this invention.
- FIG. 7 shows one of the curves of FIG. 1 in comparison with some commercially available displays.
- FIG. 8 shows the first derivative of the curves of FIG. 7.
- Curve 210a is for a commercially available plasma display
- Curve 220a is for a commercially available LCD display.
- Curves 210b and 220b are their respective first derivatives. Neither has the dynamic range necessary to drive a display with greater than 3.5 decades of response. Both curves are also outside many of the first derivative boundaries, as shown in FIG. 8. In particular, both are outside the desired first derivative range at log scene luminances of -0.6 and -2.0. Additionally, curve 220b does not meet the first derivative requirement at -1.9.
- Images having tonescales represented by curves 210a and 220a would have crushed tonal range from white to black, specifically with lifted blacks and other dark colors, and objectionably low contrast for light colored images areas (i.e. at log scene luminances around -0.6) compared to tonescales defined by this invention. Images having tonescales represented by curve 210a would also be objectionably darker from mid-tones to whites than images having tonescales like curve 110a. Images having tonescales represented by curve 220a would also be objectionably lighter from mid-tones to blacks than images having tonescales like curve 110a.
- FIG. 9 shows a schematic diagram of the image capture and display method wherein this invention is applicable.
- a digital camera 260 can be used to capture original scene parameters from an original scene 250.
- the captured scene parameters of such a camera comprise digital code values representing scene luminances, e.g. 0 to 255 for each of red, green, and blue luminances.
- the captured scene parameters can be sent to a display through an image signal processor.
- Image signal processor 270 performs transformations that comprise modifying the code values of the captured scene parameters.
- Image signal processor 270 can include any method of performing transformations on the captured scene parameters, e.g. an algorithm, a lookup table, etc.
- the modified code values are applied to the display to cause it to emit light corresponding to the modified code values, thus displaying scene reproduction 280, which is a visual reproduction of original scene 250, on the display.
- scene reproduction 280 which is a visual reproduction of original scene 250
- FIG. 10 is a four-quadrant diagram of the image capture, transformation, and display process.
- Camera curve 310 is the response of the camera to scene luminance, hi general, camera curve 310 is a defined standard, e.g. ITU HDTV standard camera curve (Rec. ITU-R BT.709-5 2002, "Parameter values for the HDTV standards for production and international programme exchange," item 1.2).
- a camera reading 350 on camera curve 310 provides a corresponding digital code value, which is provided (e.g. by broadcasting) to the display.
- Degamma curve 320 provides the transformation 360 that modifies the code values.
- the modified code values are thus transformed captured scene parameters, hi this embodiment, the modified code values are linear intensity, but other transformations as known in the art can also be used.
- the modified code values are applied via display characteristic curve 330 to provide a display response 370 such that the display emits light corresponding to the modified code values.
- Camera curve 310 is set by published standard, and display characteristic curve 330 is determined by the properties of the display.
- Degamma curve 320 is provided such that the negative log reproduced luminance vs.
- the degamma curve 320 can be provided by transforming the axes of the desired system tonescale curve 110a through camera curve 310 and display characteristic curve 330.
- the log scene luminance axis can be transformed to code value by e.g. undoing the log, mapping the resulting scene luminance to voltage through camera curve 320, and mapping the extrema of voltage to extrema of code value, e.g.
- the minus log reproduced luminance axis can be transformed to a linear intensity axis e.g. by negating, undoing the log, and normalizing the range of the resulting reproduced luminance to e.g. [0,1].
- the resulting map of code value to linear intensity commonly called a degamma curve, is well-suited for use as the first stage of image signal processor 270. Note that, for any given camera curve and display characteristic, there is a one-to-one correspondence between reproduced tone mappings and degamma curves, and that degamma curves can easily be transformed into reproduced tone mappings by reversing the above procedure.
- the method of the present invention since it starts with a reproduced tone mapping and calculates a degamma, is not guaranteed to produce degamma curves with any particular properties.
- curve 110a changes concavity multiple times but is still monotonically increasing; it is consequently difficult to represent with e.g. a polynomial function. Consequently, an image- processing path can include a lookup table to implement this degamma curve in a straightforward way, without needing to calculate a closed-form expression or other function approximating the degammma curve. This enables the use of tonescales according to the present invention which produce reproductions pleasing to viewers.
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EP08832971.9A EP2198403B1 (en) | 2007-09-21 | 2008-09-12 | Preferential tone scale for electronic displays |
CN2008801079494A CN101821774B (en) | 2007-09-21 | 2008-09-12 | Preferential tone scale for electronic displays |
JP2010525809A JP2010540987A (en) | 2007-09-21 | 2008-09-12 | Selective tone scale for electronic displays |
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US11/859,579 US8004538B2 (en) | 2007-09-21 | 2007-09-21 | Preferential tone scale for electronic displays |
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EP2198403B1 (en) | 2013-08-21 |
JP2010540987A (en) | 2010-12-24 |
US8004538B2 (en) | 2011-08-23 |
KR101263809B1 (en) | 2013-05-13 |
KR20100064385A (en) | 2010-06-14 |
CN101821774A (en) | 2010-09-01 |
TWI380280B (en) | 2012-12-21 |
WO2009042036A3 (en) | 2009-09-17 |
CN101821774B (en) | 2013-03-06 |
US20090079753A1 (en) | 2009-03-26 |
TW200931387A (en) | 2009-07-16 |
EP2198403A2 (en) | 2010-06-23 |
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