EP2347571A2 - Amélioration de contraste d'images - Google Patents

Amélioration de contraste d'images

Info

Publication number
EP2347571A2
EP2347571A2 EP09787357A EP09787357A EP2347571A2 EP 2347571 A2 EP2347571 A2 EP 2347571A2 EP 09787357 A EP09787357 A EP 09787357A EP 09787357 A EP09787357 A EP 09787357A EP 2347571 A2 EP2347571 A2 EP 2347571A2
Authority
EP
European Patent Office
Prior art keywords
color
luminance
value
values
contrast enhancement
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP09787357A
Other languages
German (de)
English (en)
Inventor
Erno H. A. Langendijk
Remco T. J. Muijs
Harold A. W. Schmeitz
Leo J. Velthoven
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
TP Vision Holding BV
Original Assignee
Koninklijke Philips Electronics NV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics NV filed Critical Koninklijke Philips Electronics NV
Priority to EP09787357A priority Critical patent/EP2347571A2/fr
Publication of EP2347571A2 publication Critical patent/EP2347571A2/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • 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
    • 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
    • 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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/44—Receiver circuitry for the reception of television signals according to analogue transmission standards
    • H04N5/57—Control of contrast or brightness
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/64—Circuits for processing colour signals

Definitions

  • the invention relates to contrast enhancement of images, and in particular, but not exclusively, to contrast enhancement of moving images of a color video signal.
  • Contrast enhancement of images is widely applied to both still and moving images to improve image quality for images perceived to have suboptimal contrast.
  • Conventional contrast enhancement methods work by modifying the luminance (brightness) characteristics for the images, e.g. by applying a non-linear function that makes bright areas brighter and dark areas darker.
  • a luminance signal for a video signal may be modified by applying a dynamic range expander function.
  • this approach may provide suitable performance for many applications, it tends to be suboptimal for many color images and may cause image quality degradation or distortion in some scenarios.
  • saturated red and blue colors are associated with intrinsic low luminance (typically about 20 % and 10 % of white respectively) and conventional contrast enhancement techniques tend to result in the undesired effect that such colors are further decreased in brightness resulting in the introduction of unnatural shadow regions.
  • an object When an object reflects only a narrow spectral band, it will have a very saturated color (e.g., 630 nm for saturated red). However, its brightness will be very low, because all the light at the other wavelengths is absorbed. Furthermore, the perceived brightness will depend on the specific color as different wavelengths with the same light intensity are perceived to have different levels of brightness. Therefore, for e.g. saturated colors, even relatively bright objects will have relatively low luminance values and the contrast enhancement will tend to reduce the brightness level further. Accordingly, for many scenes, the contrast enhancement will tend to degrade the image quality, and specifically may introduce additional shadow effects and degrade the differentiation between different colors.
  • an improved system for contrast enhancement of images would be advantageous and in particular a system allowing increased flexibility, facilitated operation or implementation, improved image quality and/or improved performance would be advantageous.
  • the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination.
  • an apparatus for contrast enhancement of a color image comprising: means for providing the color image having color values for image areas; and contrast enhancement means for performing contrast enhancement for the color image by modifying a luminance characteristic for each image area of at least some image areas in response to a color value for the image area.
  • the invention may allow improved contrast enhancement for images.
  • the invention may provide improved contrast enhancement for images having color areas that correspond to low perceived brightness and may in many embodiments prevent or reduce shadowing effects and color perception degradations.
  • the invention may in particular allow contrast enhancement which provides improved darkening of shadow regions while boosting illuminated areas.
  • the approach may in many embodiments provide improved independence of the contrast enhancement to the specific color values.
  • the invention may accordingly allow a contrast enhancement that provides a more vivid yet realistic appearance of a scene portrayed by the color image.
  • Each image area may correspond to/comprise one or more pixels. Furthermore, the at least some image areas may cover the entire image area and/or may be non-overlapping image areas. Specifically, the at least some image areas may correspond to all pixels of a digital color image.
  • the color image may be a still image or may be an image of a sequence of images, such as a frame of a video signal.
  • the color value may be represented by a color representation or a combined luminance and chroma representation.
  • the luminance values may be provided by signal values of a luminance signal and the color values may correspond to values of one or more chroma signals.
  • the color value may be a composite value comprising separate values for different color components, such as a value for each of a plurality of primary colors of a display.
  • the contrast enhancement means comprises: compensating means for generating a compensated luminance value for each of the at least some image areas in response to the color value of the image area; and means for performing a luminance contrast enhancement on the compensated luminance values.
  • the feature may provide an improved and/or facilitated contrast enhancement.
  • the feature may allow improved image quality in many scenarios while providing a low complexity implementation and operation.
  • the compensated luminance value may specifically reflect a relative perceptional brightness for the color represented by the color value relative to other colors, and specifically relative to the color white.
  • the compensating means further comprises: nominal luminance means for determining a nominal luminance value for a first image area as a function of a color value for the first image area; and luminance determining means for generating a compensated luminance value for the first image area as a function of the nominal luminance value and a luminance value for the first image area.
  • the feature may provide an improved and/or facilitated contrast enhancement.
  • the feature may allow improved image quality in many scenarios while providing a low complexity implementation and operation.
  • the nominal luminance value may specifically reflect a relative perceptional brightness for the color represented by the color value relative to other colors (and specifically to the color white) for a given (predetermined) luminance level of the image area.
  • the color value may be compensated to correspond to a specific luminance level and the nominal luminance value may indicate the perceived brightness of the color for this specific luminance level.
  • the nominal luminance value may correspond to a perceived relative brightness for a given combined value of the individual multi-component color value.
  • the nominal luminance value may correspond to a perceived relative brightness for the color represented by the color value but with a predetermined magnitude (while maintaining the same relationship between the multi- component color values).
  • the compensating means is arranged to generate the compensated luminance value for the first image area by normalizing the luminance value for the first image area relative to the nominal luminance value.
  • This may provide a particularly advantageous compensation for color variations in the image.
  • the nominal luminance means comprises a data store for storing a look-up table comprising nominal luminance values for a plurality of color values and is arranged to determine the nominal luminance value by a table look-up in the look-up table.
  • the look-up table may specifically comprise predetermined luminance values for specific colors.
  • the nominal luminance value is a maximum luminance value for the color value of the first image area.
  • This may allow a particularly advantageous contrast enhancement and may in particular provide a highly efficient compensation for impact of perceptual brightness variations as a function of colors. Alternatively or additionally, it may provide for facilitated implementation and/or operation as a maximum luminance value for a given color value may be relatively easy to determine.
  • the nominal luminance means is arranged to determine the nominal luminance as a function of a plurality of linear color component values of the color value, each color component value corresponding to a display primary color.
  • the color value may be provided by a linear Red, Green and Blue primary color component value (i.e. in accordance with a linear RGB color scheme corresponding to an RGB color scheme with a Gamma value of 1).
  • the approach may provide an efficient way of determining suitable nominal luminance values reflecting the perceptual brightness variations as a function of colors.
  • the linear color component values may specifically be used to determine a maximum luminance value for the color value.
  • the apparatus may comprise means for converting the color values from non linear color component values (such as e.g. RGB values with a gamma different than one) to the linear color component values.
  • the nominal luminance means is arranged to: generate normalized color component values by normalizing the linear color component values relative to a maximum value of the linear color component values; and determine the nominal luminance as a combination of the normalized color component values, the combination comprising a weighting corresponding to a perceptual luminance contribution for each color corresponding to a linear color component value.
  • the nominal luminance means is arranged to determine the luminance value for the first image area as a combination of the linear color component values, the combination comprising a weighting corresponding to a perceptual luminance contribution for each color corresponding to a linear color component value.
  • a facilitated and/or improved determination of the luminance value may be achieved.
  • the contrast enhancement means further comprises: means for de-compensating contrast enhanced luminance values resulting from the luminance contrast enhancement, the de-compensating corresponding to a reverse operation of the compensating means.
  • the feature may provide an improved and/or facilitated contrast enhancement.
  • the feature may allow improved image quality in many scenarios while providing a low complexity implementation and operation.
  • the de-compensation may be such that the resulting relative modification of the luminance value corresponds to the relative modification applied to the compensated luminance value by the luminance contrast enhancement.
  • the contrast enhancement means further comprises: means for, for at least a first image area, determining a relationship between a compensated luminance value for the first image area and an enhanced luminance value resulting from the luminance contrast enhancement; and modifying means for modifying a color value for the first image area in response to the relationship.
  • the feature may provide an improved and/or facilitated contrast enhancement.
  • the feature may allow improved image quality in many scenarios while providing a low complexity implementation and operation.
  • the de-compensation may be such that the resulting relative modification of the luminance value corresponds to the relative modification applied to the compensated luminance value by the luminance contrast enhancement.
  • the modifying means is arranged to multiply color component values of the color value for the first image area by a ratio between the compensated luminance value for the first image area and the luminance value for the first image area, each color component value corresponding to a display primary color.
  • the apparatus further comprises means for converting non-linear multi color component color values into linear multi color component color values; and wherein the luminance means is arranged to determine luminance values in response to the linear multi color component color values.
  • the feature may provide an improved and/or facilitated contrast enhancement.
  • the feature may allow improved image quality in many scenarios while providing a low complexity implementation and operation.
  • the contrast enhancement means comprises means for determining an illumination intensity value for each image area in response to the color value and to perform the contrast enhancement on the illumination intensity value.
  • the feature may provide an improved and/or facilitated contrast enhancement.
  • the feature may allow improved image quality in many scenarios while providing a low complexity implementation and operation.
  • a method of contrast enhancement for a color image comprising: providing the color image having color values for image areas; and performing contrast enhancement for the color image by modifying a luminance characteristic for each image area of at least some image areas in response to a color value for the image area.
  • Fig. 1 is an illustration of an example of a contrast enhancement apparatus in accordance with some embodiments of the invention
  • Fig. 2 is an illustration of an example of a contrast enhancement processor in accordance with some embodiments of the invention.
  • Fig. 3 is an illustration of an example of a luminance transfer characteristic for a contrast enhancement algorithm.
  • Fig. 4 is an illustration of an example of a method of contrast enhancement for a color image in accordance with some embodiments of the invention.
  • Fig. 1 illustrates an example of a contrast enhancement apparatus for performing contrast enhancement on one or more color images.
  • the contrast enhancement performed by the apparatus will be described with focus on contrast enhancement for a single digital still color image.
  • contrast enhancement may for example be applied to sequences of images, such as video frames of a digital video signal, or directly to analog representations of color images, such as to an analog color video signal.
  • the contrast enhancement apparatus comprises a color image source 101 which is arranged to provide a color image which in the specific example is a digital still image represented by a color value for each pixel of the image.
  • the color value is specifically a set of multi-component color values corresponding to a specific color space.
  • a value is provided for each primary color of a display to present the image.
  • the color value may contain three multi-component color values corresponding to e.g. the color components of an XYZ or RGB color space.
  • the color value for each pixel contains three drive values for respectively the Red, Green and Blue colors of an RGB color space.
  • the image may be represented by luminance and chroma values that may further be analog or digital representations.
  • a separate color value may not be provided for each image pixel but rather a color value may provide color information for an image area that may correspond to a plurality of pixels.
  • luminance data may be provided on a per pixel bases whereas the color values are provided on a per pixel block basis, where each pixel block comprises a plurality of pixels (e.g. color data may be provided for blocks of four pixels).
  • an image area may be a pixel block comprising one or more pixels.
  • the color image source 101 may for example provide the color image by retrieving it from an internal source, such as a hard disk or other storage means, or may e.g. comprise a receiver for receiving the color image from an external source.
  • the color image source 101 is coupled to a contrast enhancement processor 103 which is arranged performing contrast enhancement on the image.
  • the contrast enhancement includes modifying a luminance characteristic for at least some image areas depending on a color value for the individual image area.
  • the contrast enhancement processor 103 performs contrast enhancement which does not only consider luminance information but also depends on the color of the image area being modified. For example, the adjustment of a pixel value depends not only on the brightness but also on the color of that pixel.
  • the contrast enhancement processor 103 normalizes the luminance characteristic of image areas such that the luminance of the image area is normalized with respect to the maximum luminance of the color of the image area prior to the contrast enhancement. This normalization procedure effectively provides an approximation of the illumination intensity in a scene.
  • the contrast enhancement processor 103 then proceeds to perform contrast enhancement on the normalized image by darkening shadow regions and increasing the brightness in illuminated areas regardless of the color.
  • the resulting contrast enhanced image can then be de-normalized to provide a contrast enhanced image corresponding to the original image.
  • the approach allows the contrast enhancement to be adapted to the local color conditions in order to provide an improved contrast enhancement.
  • the contrast enhancement of different colors may be harmonized to provide a more consistent contrast enhancement. This can in particular prevent darkening of relatively bright colors that have low luminance values due to the color rather than the relative brightness.
  • saturated colors associated with an intrinsic low maximum luminance e.g. red and blue
  • saturated colors associated with a high intrinsic maximum luminance such as green and yellow.
  • the result may be a clearer and more vivid image with realistic shadow effects and clearer color differentiation.
  • the compensation of the luminance may specifically result in the compensated luminance corresponding to a non-color specific illumination intensity for an image area rather than a color specific luminance value for the image area.
  • the compensated luminance may reflect the strength of white light falling on an image object rather than the perceived luminance resulting from light being reflected by the image object.
  • the contrast enhancement process is applied to illumination values rather the original luminance values.
  • Fig. 2 illustrates more detailed elements of the contrast enhancement processor
  • the contrast enhancement processor 103 receives data in the form of multi color component color values comprising three non-linear component values.
  • a three component non-linear color format is used in the specific example, such as e.g. an XYZ format. The following description will focus on the color values comprising a Red,
  • the contrast enhancement processor 103 accordingly comprises a color scheme converter 201 which receives the non- linear RGB image data from the color image source 101.
  • the color scheme converter 201 then proceeds to convert the color scheme into a linear color scheme, which in the specific example is a linear RGB color scheme.
  • the color scheme converter 201 performs the conversion: where R ⁇ , G l ⁇ and B 1J denote the input red, green and blue sub-pixel drive values at row i and pixel positiony, respectively, and RiJ" 1 , G 1 J 1 " and B 1 J 1 " represent the subpixel drive values in the linear light domain.
  • the color scheme converter 201 is coupled to a luminance compensation processor 203 which generates compensated luminance values for the image areas where the compensated luminance values depend not only on the luminance values of the image areas but also on the color values of the image areas.
  • the luminance compensation processor 203 comprises a nominal luminance processor 205 arranged to determine a nominal luminance value for each image area, and specifically for each image pixel.
  • the nominal luminance value is specifically a relative luminance value for the color relative to a white color.
  • the nominal luminance value may reflect a perceptual brightness or luminance level for the color for a given light intensity.
  • different colors will have different nominal luminance values as the eye will perceive different colors with different brightness despite them having identical light intensities. For example, the same amount of light of a blue color will tend to be perceived to be ten times less bright than the same amount of light of a green color.
  • the nominal luminance processor 205 may for example comprise a data store which stores a look-up table comprising predetermined nominal luminance values for different color values at a given light intensity. The nominal luminance processor 205 may then normalize the color value to that light intensity and perform a table look-up that identifies the stored nominal luminance value for the color closest (or identical) to the color represented by the color value.
  • the nominal luminance value is a maximum luminance value for the given color.
  • the nominal luminance value is a relative value for the perceived luminance value for the color assuming that the light intensity is at the maximum level that can be represented by that color representation.
  • the maximum luminance value in this case may reflect both an impact of the color on the perceived luminance (due to the eye and brains relative brightness perception for different colors) as well as an impact of the varying ability of the color scheme to provide maximum light intensities for different colors.
  • a white signal may be represented by the component values (1,1,1) whereas the maximum light intensity that can be provided for e.g. the color red may correspond to (1,0,0), i.e. the maximum light intensity that can be provided will in this case be reduced for red relative to some composite colors.
  • the nominal luminance processor 205 calculates the nominal luminance value for a color value directly from the linear multi component color values, i.e. from the linear RGB values. The calculation specifically comprises an initial normalization of the color values relative to a maximum value of the linear color component 5 values followed by a combination of the normalized values taking into account the perceptual luminance contribution for each color corresponding to a linear color component value.
  • the nominal luminance processor 205 proceeds to normalize the linear RGB values by dividing each value by the largest of the multi component values:
  • the relative RGB values corresponding to the maximum intensity for that color is determined (assuming that RGB values are represented as values in the range of [0,1]).
  • this maximum luminance also reflects the intensity limit of the color scheme for different colors (e.g. for a pure green light, the resulting maximum value will be (0,1,0) and for a composite white light, the resulting maximum value will be (1,1,1)).
  • the normalization may be relative to the combined luminance for the pixel value, such as e.g.:
  • the nominal luminance processor 205 then proceeds to calculate the perceived luminance for the normalized color value taking into account the eye's and brain's relative perception for the three primary display colors. Specifically, the nominal luminance processor 205 combines the multi component values with each value being weighted by a value reflecting the perceived brightness contribution from the corresponding primary color.
  • the nominal luminance processor 205 uses a weighted summation:
  • the luminance compensation processor 203 furthermore comprises a luminance processor 207 which calculates a luminance value for each image area (and specifically pixel in the current example) in response to the color value for that image area.
  • a luminance processor 207 calculates the luminance for pixel (i,j) as: .
  • the nominal luminance processor 205 and the luminance processor 207 are coupled to a compensated luminance processor 209 which proceeds to calculate a compensated luminance value for the pixels as a function of the nominal luminance value and the luminance value for the pixel.
  • the compensated luminance value may be calculated in response to only these parameters without taking any other parameters into account.
  • the compensated luminance processor 209 calculates the compensated luminance value for a pixel by normalizing the luminance value for the pixel relative to the nominal luminance value for the pixel.
  • the compensated luminance processor 209 can calculate the compensated luminance as a relative luminance of the pixel relative to a maximum luminance value.
  • the compensated luminance may be calculated as:
  • This value corresponds to an estimation of the illumination intensity of the pixel (i.e. is compensated for the brightness effect of the color information) and is specifically calculated by normalizing the luminance of the input pixel relative to the maximum luminance achievable for the color of the pixel.
  • the RGB values may be in the range of [0,1] resulting in the illumination intensity value I also being in the range of [0,1].
  • the luminance compensation processor 203, and specifically the compensated luminance processor 209 is coupled to a luminance contrast enhancement processor 211 which is fed the compensated luminance values, and specifically the illumination intensity values I u , and which proceeds to perform a luminance (only) contrast enhancement on the compensated luminance values.
  • the contrast enhancement applied to the image by the luminance contrast enhancement processor 211 considers only compensated luminance characteristics and does not consider any color parameters or characteristics.
  • any suitable contrast enhancement process based on luminance may be used.
  • a simple non- linear function may be applied to the compensated luminance values resulting in a reduction of low luminance values and an increase in high luminance values.
  • the transfer characteristic of FIG. 3 may be applied. It will be appreciated that a large number of luminance contrast enhancement algorithms will be known to the skilled person and that any suitable such algorithm may be used without detracting from the current invention.
  • the contrast enhancement is applied to the illumination signal I instead of being applied to the luminance Y.
  • the enhancement operation may be represented by: J *
  • the contrast enhancement processor 103 further comprises a de-compensation processor 213 which is capable of compensating the contrast enhanced luminance data for the compensation of the original luminance values performed by the luminance compensation processor 203.
  • the de-compensation processor 213 may perform a de-compensation which corresponds to the reverse operation of the luminance compensation processor 203.
  • the normalization relative to the nominal luminance value may be reversed.
  • the de-compensated luminance value for a pixel may be determined by multiplying the contrast enhanced compensated luminance value by the nominal luminance value associated with the color of that pixel.
  • the de-compensation processor 213 performs an indirect de-compensation by directly scaling the color coordinates of the pixel dependent on the contrast enhanced color value.
  • the de-compensation processor 213 comprises a luminance relationship processor 215 which determines a relationship between the contrast enhanced luminance value and the compensated luminance value prior to the contrast enhancement.
  • the relationship may specifically be a ratio indicating the relative change in the luminance value resulting from the contrast enhancement.
  • the luminance relationship processor 215 calculates the ratio:
  • the luminance relationship processor 215 is coupled to a color value modifier
  • the color value modifier 217 which is also coupled to the color scheme converter 201.
  • the color value modifier 217 proceeds to modify the color values of the image to reflect the relationship between luminance values which has been introduced by the contrast enhancement.
  • the color value modifier 217 may simply multiply the color component values of a color value for a pixel by the ratio between the luminance values of the pixel before and after contrast enhancement.
  • the color value modifier 217 is a multiplier multiplying the individual linear RGB color values by the ratio between the compensated luminance value (the illumination intensity) before and after contrast enhancement.
  • the color values of the enhanced output are generated by scaling the input linear RGB-data values by the ratio of the enhanced and original illumination.
  • the luminance compensation processor 203 may accordingly be considered to perform a transformation from a luminance domain to an illumination intensity domain and the de-compensation processor 213 may be considered to perform the complementary transformation from the illumination intensity domain to the luminance domain.
  • the resulting RGB color values are then fed to a second color scheme converter 219 coupled to the color value modifier 217 and arranged to convert the linear RGB values to non-linear RGB values corresponding to the format used for the input data to the first color scheme converter 201.
  • the described approach may provide an improved contrast enhancement and may for example reduce the risk of introducing unnatural shadow effects to color images.
  • the approach allows critical areas to be identified as having the same illumination intensity allowing them to be mapped in a consistent manner.
  • the illumination map consisting of compensated luminance values provide clearer differences between illuminated areas and shadow areas. Contrast enhancement of the illumination values will therefore increase the shadow intensity while maintaining a natural balance between objects.
  • Fig. 4 illustrates an example of a method of contrast enhancement for a color image.
  • the method initiates in step 401 wherein a color image is provided having color values for image areas.
  • Step 401 is followed by step 403 wherein contrast enhancement is performed for the color image by modifying a luminance characteristic for each image area of at least some image areas in response to a color value for the image area
  • an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the invention may be implemented in a single unit or may be physically and functionally distributed between different units and processors.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Image Processing (AREA)
  • Processing Of Color Television Signals (AREA)
  • Color Image Communication Systems (AREA)
  • Facsimile Image Signal Circuits (AREA)

Abstract

Un appareil est conçu pour permettre une amélioration du contraste d'une ou plusieurs images en couleurs. L'appareil comprend une source d'image (101) qui transmet l'image en couleurs ayant des valeurs de couleurs relatives à des régions de l'image, chaque région de l'image pouvant correspondre en particulier à un pixel. Un processeur d'amélioration de contraste (103) met en œuvre une amélioration de contraste sur l'image en couleurs en modifiant une caractéristique de luminance relative à au moins certaines régions de l'image en réponse à la valeur de la couleur relative à la région de l'image. En particulier, le processeur d'amélioration de contraste (103) peut produire des valeurs de luminance compensée relatives à des pixels en normalisant les valeurs de luminance par rapport à une valeur de luminance nominale relative à la couleur des pixels. Une amélioration de contraste de luminance est alors exécutée sur les valeurs de luminance compensée. L'approche peut permettre une qualité d'image améliorée et peut, en particulier, réduire l'apparition d'effets d'ombre artificiels dus à des variations de couleurs.
EP09787357A 2008-10-13 2009-10-05 Amélioration de contraste d'images Withdrawn EP2347571A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP09787357A EP2347571A2 (fr) 2008-10-13 2009-10-05 Amélioration de contraste d'images

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
EP08166453 2008-10-13
PCT/IB2009/054336 WO2010043996A2 (fr) 2008-10-13 2009-10-05 Amélioration de contraste d'images
EP09787357A EP2347571A2 (fr) 2008-10-13 2009-10-05 Amélioration de contraste d'images

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EP2347571A2 true EP2347571A2 (fr) 2011-07-27

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JP (1) JP2012505460A (fr)
KR (1) KR20110083663A (fr)
CN (1) CN102187657A (fr)
WO (1) WO2010043996A2 (fr)

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JP2012505460A (ja) 2012-03-01

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