EP1532580A2 - Procede d'accentuation de couleurs - Google Patents

Procede d'accentuation de couleurs

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Publication number
EP1532580A2
EP1532580A2 EP03749058A EP03749058A EP1532580A2 EP 1532580 A2 EP1532580 A2 EP 1532580A2 EP 03749058 A EP03749058 A EP 03749058A EP 03749058 A EP03749058 A EP 03749058A EP 1532580 A2 EP1532580 A2 EP 1532580A2
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EP
European Patent Office
Prior art keywords
color
color space
pixel
value
space
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.)
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Application number
EP03749058A
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German (de)
English (en)
Inventor
Paul Reed Smith
Gary E. Gilbert
Ted Sabety
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Paul Reed Smith Guitars LP
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Paul Reed Smith Guitars LP
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Publication date
Application filed by Paul Reed Smith Guitars LP filed Critical Paul Reed Smith Guitars LP
Publication of EP1532580A2 publication Critical patent/EP1532580A2/fr
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/12—Picture reproducers
    • H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
    • H04N9/3102—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM] using two-dimensional electronic spatial light modulators
    • H04N9/312—Driving therefor
    • H04N9/3123—Driving therefor using pulse width modulation
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T11/00—2D [Two Dimensional] image generation
    • G06T11/001—Texturing; Colouring; Generation of texture or colour
    • 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
    • H04N9/00—Details of colour television systems
    • H04N9/12—Picture reproducers
    • H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
    • H04N9/3179—Video signal processing therefor
    • H04N9/3182—Colour adjustment, e.g. white balance, shading or gamut

Definitions

  • the present invention relates generally to color processing systems and more specifically to a color accentuation system and a component of a color processing system.
  • Color processing falls into two general categories, namely light projections or displays which are known as additive color systems and pigment or printing systems which are known as subtractive color systems.
  • Color correction systems have been developed to correct for errors in the reader or scanner of the original material, signal transmission or limitations of the display or printing process. Color correction systems are also used to enhance images or video taken under sub-optimal conditions (for example, poor lighting). In the printing process, the correction can be directed to ink migration and physical color discontinuity. In an image or a video display, color correction can be for errors in the processing system and/or for changing the quality or color of the picture to meet certain criteria and/or tastes.
  • the present color accentuation system will help improve digital cameras, TV and other video display devices, video recording devices, and HDTV picture quality in both large and small formats. It will also improve color image printing. Digital still cameras and digital video cameras may have a button or command that triggers various levels of accentuation that would improve the picture quality. For example, one might take a picture on a dull, overcast day. When the accentuation button is pressed, the image will look like it was taken on a bright day. In another example, pictures taken with florescent lighting will look as if they were taken with more natural light.
  • the present invention is directed to the concept of accentuating the ultimate color image to be more vivid, color diverse, interesting to the eye and having higher color contrast.
  • the present invention would be compatible with almost any video or print media.
  • This patent description translates well to the CMYK color space, which is the system generally associated with the printing industry.
  • CMYK stands for Cyan, Magenta, Yellow, and Black. These colors are related to the primary colors, red, yellow and blue, with black being considered by this invention as the absence of color.
  • TN's and video use the RGB (Red, Green, and Blue) and Y Cb Cr and its related color spaces.
  • the color accentuation system described herein can be converted into any known or new color space or system, whether additive (light) or subtractive (ink, paint, etc.) using well-known algebraic transformations.
  • additive color spaces the same equations can be used if certain adjustments are made to mitigate for the fact that the color components in some of these color spaces are very different hues from the primary colors. This approach achieves the benefit of the invention, with computational efficiency at the sacrifice of precision, which maybe an acceptable trade off in some applications.
  • the primary colors are red, yellow, and blue.
  • Rainbow colors are generally considered the vivid, bright colors and are either a primary color or two primary colors mixed at some ratio/percentage.
  • a subtractive primary color space or process as the percentage of the lowest percentage third color component increases, the overall color becomes more dirty and eventually becomes shades of grays and/or browns. This directly relates to additive color processes and spaces through color space conversion.
  • the system determines the relative magnitude of each color component.
  • the color components are the set of colors that are the axes in a given color space. For example, in Red, Blue, Yellow, RBY (the primary color space), R, B and Y are the color components.
  • the invention selects and adjusts the magnitude of one or more of the colors as a function of the determined relative magnitudes of each color component. The type and amount of the adjustment is a function of the relative magnitude differences between the components. One or more of the magnitudes is adjusted to change the relative magnitudes.
  • the difference in a subtractive color space e.g., CMY(K)
  • RGB additive color space
  • the lowest color component is reduced in the subtractive color space, and the highest color component is increased in the additive color space.
  • black (K) is not considered a color in the initial color accentuation step.
  • the invention can be applied to an image on a pixel by pixel basis (where the accentuation function is calculated and applied to each pixel individually) or on an area by area basis (where the function is calculated for an area of the image and the same function applied to each pixel in the area).
  • An area in an image is a set of adjacent pixels in the image that have substantially the same color, in other words, substantially the same color component magnitudes.
  • Scaling functions and compensations may also be used. These include brightness compensation, dominant color compensation and saturation compensation or adjustments using various scaling functions.
  • the arguments of the scaling functions may include the difference of the magnitude of the color components relative to each other or other arguments.
  • Figure 1 is a color processing system in which the present invention can be incorporated.
  • Figure 2 is a subtractive space color wheel.
  • Figure 3 is a single slice color wheel for RYB from color pipe of Figure 5 with scaling functions.
  • Figure 4 is a look up table in CMYK correlating the original to the accentuated color.
  • Figure 5 is a conceptual view of the color pipe.
  • Figure 6 is a flow chart of color accentuation according to the principles of the present invention.
  • Figure 7 shows graphs of a scaling function and its components incorporating the principles of the present invention.
  • Figure 8 shows graphs of various scaling functions incorporating the principles of the present invention.
  • Figure 9 shows graphs of additional scaling functions incorporating the principles of the present inventions.
  • the core of this invention is developed from the primary colors (Red,
  • the present invention can be used in two modes.
  • a first mode an image, that is encoded using any first color space, is converted into the color component magnitudes of a second color space and has the accentuation function applied in that color space.
  • the resulting image can be converted back to the original color space.
  • the accentuation function can be determined in a first color space and then the accentuation function is transformed to any other color space so that an image need not be converted—the transformed function is applied to the image in the color space of the image. It is also possible to approximate the calculation in such a way that the image and scaling function is not entirely transformed into another color space, but parts of the algebraic transformation are used to calculate intermediate results that provide a close approximation of the invention.
  • CMY and RGB RGB being used in video applications and which is also an additive color space.
  • CMY(K) a subtractive color space
  • RGB and CMY(K) color spaces have known direct mathematical relationships to each other.
  • magenta in the CMYK color space has a small blue component, operations on magenta affect two colors (red and blue), not one (red).
  • the present system looks at the relative differences between the colors and makes the correction based on a function of such differences.
  • CMYK K
  • the black is not adjusted in the initial function. But black may still be part of the color percentage, so that the conversion of CMYK to another color space is accurate.
  • RGB CMY
  • the conversion of RGB to CMY does not include the black component.
  • CMY color that is substantially equal in color, they are "dirty" in color.
  • the lowest magnitude value color component of the three colors creates, in the combination the other two colors, a pastel dirtiness, grayness, brown-ness or a perceived lack of contrast, vividness or perceived sharpness.
  • the present invention creates a higher color contrast, sharper, clearer picture or color and reduces the effect of the lower of the three color components, pixel by pixel or area by area.
  • the accentuation adjustment may be to one or more of the three colors.
  • a color space component (CSC) is provided at 30.
  • CSC color space component
  • the accentuation process is applied in at least one of two ways.
  • the relative magnitude of the color components is determined at 34a or 34b.
  • the relative magnitude determination at 34 may be a single step and may be performed before the determination of the type of color space at 32.
  • the color space is pre-defined, and the method would include only one leg 34-42. There is no need for a decision in the process of determining the color space; that is, the color space is typically pre-determined by the design of the entire imaging signal chain.
  • the difference between the MAX and MID is determined at 36a. If it is a subtractive color space, the difference between the MID and the MDSf is determined at 36b. These differences are used at 40a and 40b, respectively, to modify the color components as a function of these differences.
  • the output is provided as a new color space component (CSCnew) at 44.
  • various scaling functions 38a or 38b may be used in modifying the color components, as well as various compensations at 42a or 42b.
  • the compensation at 42a and 42b may be part of the color component modification 40a and 40b or may be a post-process modification.
  • the selection of scaling may precede the steps of 34, 36 or 40 and may be incorporated as part of step 40. In the determining the relative magnitude of the color components, it may require normalizing the color component value ranges in cases where the color components do not have the same numerical range.
  • the color space components may be converted to a different color space using the previously developed modified color component as a function of the differences, or the function of the differences may be converted to other color spaces.
  • the interaction of the various components of the method will be described more fully below. It is possible to approximate the result by using any additive color space components whose value ranges are normalized in the equation otherwise derived, for example, for RGB, as further discussed below.
  • a pixel containing the collection of values for individual color components can be analyzed in percentage magnitudes of those color components. This is the relative magnitude relative to full scale. For example, in a 24 bit, 8 bits per color, 3 color space like RGB, the R, G or B value is divided by 255 to calculate the percentage. In the CMY(K) space, the new value of the minimum- value color component (other than black) is calculated based on one of the following equations:
  • MIN is the color component (excluding Black, K) in a pixel or area that has the minimum percentage value
  • MID is the color component (excluding Black, K) in a pixel or area that has the middle percentage value
  • MAX is the color component (excluding K, Black) in a pixel or area that has the maximum percentage value
  • MDSf New is the accentuated minimum percentage value color component (excluding
  • the modifying or scaling function f(%MID - %MIN) result may be set to zero if the difference between MID and ML is very small.
  • the scaling function f may be a constant times (%MID - %MLN), as in equation (a).
  • the modifying function f(%MID - %MLN) may also increase, decrease or change the adjustment signified by the difference as a function of any of the color components present or the specific percentage relationship of the color components.
  • the scaling function for its equivalent modifies one or more of the component color values based on the argument of the difference between the two lowest percentage color component values. This can be algebraically converted to any other color space using well-known mathematical conversions.
  • Accentuation may be equivalently performed based on lookup tables.
  • pre-calculation of the scaling function f can be performed and a look-up table created using the non- normalized values for R, G and B as input and output.
  • the new color component values are determined by matching the original color component values to those in the table and reading the new color component values out of the table for that color component set.
  • the middle two columns of Figure 4 would be a partial example of such a lookup table.
  • the value (%MID - %MIN) may be utilized as an offset into a lookup table or a two- dimensional index of (%MAX, %M1D), whether MID and MLN are expressed as percentage of full scale value or as the actual numerical values.
  • the non-normalized values may be used.
  • Common assembly-level computing instruction sets and higher-level languages such as C, C++, and many others have inherent indexing capabilities that make such an implementation very efficient. The need for complicated mathematical calculations being performed during run time can be eliminated or reduced.
  • the lookup tables can be directly coded into read only memory in hardware logic implementations .
  • FIG. 1 illustrates a color processing system 20 for reproducing a color image 10, as image 12, on a media 14. If this is a printing process, then media 14 is the object on which the printing is performed. If it's a display like a television or CRT, then media 14 is a display.
  • the color processing system 20 generally includes a lens 22 providing input signals of the image 12 to a color separator 24.
  • the color separator 24 provides a minimum of three colors and in this example, four color signals to the signal processor 26.
  • the signal processor 26 then provides appropriate drive signals to projectors or printers 28, depending upon whether it is a printer or a light projector.
  • projectors/printers are shown but other projector or printers may be used depending upon the number of colors being processed. For example, it could be a three color additive system, a four color separation system, or a six color system.
  • the color processing system 20 can be thought of as a combination of components to process the color signal.
  • the lens 22 would introduce a color image to a color encoding system 24 that color separates a pixel into color components for a given color space.
  • the encoded image information is presented to a signal processor 26 that applies color accentuation using the scaling functions and may also apply color space transformations.
  • the image information is transferred to the projector/printer 28 to recombine color components through either a light projection, ink printing system, or other recombinant method to form the processed image 12.
  • digital data comprising the original encoded image or the processed image can be stored as digital files on digital recording media and/or transmitted as digital files such that the components of the system depicted in Figure 1 may be separated physically and not reside within a single apparatus.
  • the color accentuation of the present method would be in the signal processor 26.
  • the signal processor 26 may be part of the original camera or scanner and/or may be in the signal processor 26 for the projector or printer.
  • the signal processor 26 may be part of a device that either plays back pre-recorded video media or processes video signals received by the device. These may include, for example, television or other display devices, as well as DND-R or other video storage devices.
  • the signal processor 26 may include well-known signal correction software modified to incorporate the present invention.
  • CMYK color separation system
  • CMYK color separation system
  • Some of these systems deal with hue (H), saturation (S), luminance or lightness (L, Y), and chrominance (C) or the difference of a three-component color system (U, N; Cb, Cr; Pb, Pr).
  • Saturation is the degree of color intensity.
  • Hue is also known as the name of the color and luminance is the degree of light/dark of the color.
  • any color on the outside of the wheel is vivid and/or pure. Any color on the outside of the wheel is either one primary color or combinations of two primary colors, as in a rainbow.
  • a subtractive color space if any amount of a third primary color is added to the outside of the wheel, the color starts becoming dirty, less vivid, and moves into the interior of the wheel. As it approaches the center, it becomes dirty gray or brown, depending on its component colors. Eventually, as the color component percentages become large and near equal, the color becomes dirty gray which is the center of the wheel.
  • the Figure 3 wheel is the 100% slice through a solid color cylinder ("color pipe"), the surface of which contains the three primary colors Red, Yellow, Blue, equally spaced along the circumference.
  • the slice of the color cylinder ranges in intensity from 0% at one end of the cylinder to 100% at the other end.
  • Figure 5 shows a conceptual view of the color pipe.
  • the percentage shown on the color pipe signifies the maximum value of any of the three primary colors. Thus, if Red is the maximum color at 80%, the color wheel would be the 80% wheel of the color pipe.
  • a set of scaling function adjustments S 2 , S 3 and S 4 are also shown. They illustrate that the scaling function varies as the color moves from dirty, for example, toward pure. S 2 shows adjustment for an original color close to a pure color. S 3 and S show additional smaller adjustments.
  • the arrows show the adjustment of the value of the color components using a scaling function that modifies the total color component values so that the total color moves towards the outside vivid portion of the circle.
  • the scaling function is based on differences between color component values.
  • the length of the arrow represents the relative adjustment for one example scaling function.
  • the amount of color accentuation relates directly to the arrow length for that pixel. The closer a color is to the outside of the wheel, the more it is accentuated towards a vivid pure color on the outside of the wheel. However, as explained below, this process can break down for pixels already very close to the edge of the color wheel, that is, for pixels that already are substantially a primary color.
  • the scaling function is designed to attenuate itself so that the color accentuation occurs primarily in an annular ring around the center of the color wheel.
  • the example is shown as reducing the percentage of the lowest color, the other color components may also be adjusted.
  • the highest may be increased by itself or in combination with lowering the lowest.
  • the middle color can be raised. All of these reduce the effect or contribution of the third or lowest color.
  • the scaling function may be a modification of the numerical difference of the middle and lowest percentage of color components, as discussed with respect to equations (b)-(e) for a subtractive color space.
  • the primary colors have different degrees of dirtiness. Blue contributes more dirtiness than red which contributes more than yellow for example. Thus if blue is the lowest percentage color component it will be reduced more than if red or yellow was the lowest percentage color component.
  • different colors saturate quicker than others and differently in different color spaces. For example, in typical media devices, red often saturates quicker or more than green or blue and, thus, would use a different scaling function. In the embodiment for an RGB color space, each of R, G and B have distinct scaling functions. Saturation is discussed in detail below.
  • equations describing calculations in a given color space may be transformed algebraically into different but functionally equivalent calculations in a different color space using well-known mathematical transformations such that the results are substantially equivalent.
  • equation (b) which is defined for use in a subtractive color space (e.g. CMYK)
  • RGB additive color space
  • %MAX New %MAX + f(%MAX-%MLD) * (100% - %MAX).
  • f(%MAX-%MID) %MAX + f(%MAX-%MLD) * (100% - %MAX).
  • %MAX New %MAX + a*(l - e (' * (%MA ⁇ - %MID ») *o /oMA ⁇ * (100 o /o _ %MAX)
  • a and b are numerical constants.
  • the nonlinear equation (g) can be transformed into any other color space.
  • the practitioner of ordinary skill in the art will recognize that the scaling function for use in RGB space can be itself transformed into other color spaces using well-known transformations, including to YCbCr or YUN.
  • %MAXnew %MAX*f(%MAX-%MLD).
  • equation (f) is an example of equation (h).
  • the form of equation (h) may provide computational efficiencies and is easier to manipulate in conversions between color spaces.
  • %MAX is the number equal to the value of the MAX color component divided by its range.
  • the look-up table implementations can use the component values rather than percentages.
  • a more general form of non-linear scaling function of f(%MAX-%MID) for RGB (or other additive color spaces) can be used that avoids over-saturating color by having a shape that rolls-off when the MAX-MID approaches its maximum.
  • a scaling function that has six parameters to adjust the overall shape of the function to meet the requirements of particular display or output devices is:
  • This scaling function has six parameters, a, b, c, d, g, and h that can be adjusted to change the shape of the scaling function.
  • the 255 divisor in these equations will be changed to be equal to 2 (# its Per comP ° nent >-l.
  • the parameters are typically set so that there is an initial upward sloping or monotonically increasing section near where MAX-MLD is close to zero that then enters a concave downward or plateau peak area where the color accentuation effect is at its maximum, which then rolls off back down or monotonically decreases toward the minimum effect to be applied for large values of MAX-MID.
  • Figure 7 The percentage of scaling from zero to 100% is graphed as a function of the difference from 0 to 255 for the three functions Zl, Z2 and Z3 and the product f(%MAX-%MID).
  • the initial rise or increase from zero can be between and extend over a portion or all of 0% to 50% of the range of differences.
  • the peak which may be a plateau, may be between and extend over a portion or all of 0% to 80% of the range of differences.
  • the final decline or decrease may be between and extend over a portion or all of 40% to 100% of the range of differences.
  • Figure 8 shows examples of four other scaling functions using equation (i).
  • Figure 9 shows two other examples (superl and super2) of the scaling function compared to an exponential (exp) and linear (liner.4) version.
  • the constants for exp, superl and super2 for equation (i) are:
  • the linear f(MAX-MID) is 0.4 times (MAX-MID).
  • a review of the curve for superl shows a peak or relative plateau above 0.5 in the range of 80 to 150 or approximately 27% of the total difference range.
  • Super2 peaks or plateaus above 0.3 in the range of 55 to 145 or 35% of the total difference range.
  • super2's rises and falls are more equal over 22% of the total difference range. Both are at zero over 30% ⁇ of the total difference range.
  • This general scaling function shape can be adjusted to optimize the color accentuation effect to meet the requirements of particular storage, transmission, display or output devices.
  • the practitioner of ordinary skill will recognize that a variety of algebraic functions can be devised that produce an equivalent shape that provides maximum color accentuation in a region between the lowest values and highest values for MAX-MID (in an additive color space) or the lowest values for MID-MrN in a subtractive space.
  • the equation (i) can be transformed into any other color space. Alternatively, it can be used in some additive color spaces, for example, Y Cb Cr or Y U V, as an approximation, as described below.
  • the algebraic transformation of the equation from a subtractive space to an additive space converts the comparison of the two minimum color component magnitudes to examining the magnitudes of the two maximum color components and scaling the color component values based on the difference between the maximum and middle values of the three color components.
  • lowering the magnitude of the mimmum color in CMYK is the equivalent of raising the magnitude of the maximum color in RGB space.
  • One compensating scaling function takes the MAX-MID argument, but also adjusts the value of the MED component so that the pixel color position on the color wheel moves radially outward. Adjustment of the MAX produces an equivalent effect. In other words, all three color components are adjusted so that the effect is to push the apparent color towards the outer ring of primaries on a color wheel.
  • Y green is increased relative to the other two colors.
  • Cb blue is increased relative to the other two colors.
  • Cr is increased, red is increased relative to the other two colors.
  • Y Cb Cr again, only one color is more dominant and moves further from another color.
  • green is increased while blue is decreased.
  • Y minus Cb green is increased while blue is decreased.
  • Y minus Cb one will see that it includes green minus blue.
  • Y minus Cr it includes the difference of green minus red.
  • Cb minus Cr it includes the difference of blue minus red.
  • R-G 2.409*(Cr - 128) + .391*(Cb - 128) (k)
  • R-B 1.596*(Cr - 128) - 2.018*(Cb- 128)
  • G-B -.813*(Cr - 128) - 2.409*(Cb - 128)
  • a logic table determines whether R, G or B is the MAX or MLD, and MAX-MLD is already calculated. This difference is used in a look-up table to determine the scaling function F of RGB for the corresponding MAX. For the present example, green G is assumed to be the MAX and, consequently, green G is to be accentuated.
  • the following equations are an approximation of the adjustment:
  • Ynew Y + .504*F*ANG(G) (1)
  • Crnew Cr - .368*F*ANG(G) Cbnew - Cb - .291*F*ANG(G)
  • ANG is an average value for R, G, or B and generally selected to be in the middle portion of the difference range as discussed with respect to Figures 8 and 9.
  • the argument for ANG is the color component that is to be accentuated, hence, in this example, it is ANG(G).
  • ANG can be locally calculated in the region surrounding the location of the pixel.
  • brightness compensation acts to offset the overall brightness change in an image after the initial color accentuation takes place.
  • color accentuation acts to brighten a pixel by adjusting one color component upward in value based on the color accentuation function.
  • the accumulation of accentuation across an image therefore increases the "brightness" of the image.
  • the brightness compensation may affect all three components in a pixel proportionally to the amount of accentuation on the accentuated component in the pixel.
  • %MAXnew2 %MAXnew * BrightnessScale *(%MAXnew - %MAX) + %MAXnew
  • a user controlled or set multiplier called BrightnessScale is a parameter used to further scale the magnitude of the brightness compensation operation.
  • CMY and CMYK color spaces as well as using the brightness, luminance or lightness L of other polar color spaces for scaling.
  • the operation of this process may be transformed through standard color space conversions and are equivalent.
  • Brightness compensation may also be performed to preserve the characteristic brightness as described by the "Y" value in color spaces YUN, YCbCr, etc.
  • the process is as follows:
  • the brightness compensation in Y may scale all three color components or just one color component.
  • the number of color components scaled may be a function of the transformation equations for Y.
  • the brightness correction should not substantially diminish the results of the color accentuation.
  • the color accentuation is applied in Y Cb Cr space directly, then the brightness adjustments can take place in the scaling function and conversion into and out of RGB space described above are skipped.
  • color accentuating the image can make the image appear "over saturated” in that dominant color. This is especially the case because color imaging devices have a finite range of color component values. The result may be unsatisfactory. Dominant color compensation may be used to limit the amount of color accentuation that is applied to a dominant color to minimize over saturation of the dominant color in the frame or image.
  • Dominant color compensation begins with measuring the image as a whole for the relative prominence of a particular color component.
  • RGB space an additive color space, this test is for Red, Green, and Blue.
  • CMY or CMYK color spaces subtractive color spaces, the test is for Cyan, Magenta, or Yellow, where black is ignored in the CMYK color space.
  • One preferred embodiment is to average the separate color component values across the entire image. A result for each color is obtained. For the RGB color space, an average value for each of Red, Green, and Blue are obtained. The highest value is considered the prominent color.
  • the difference between the highest average color value and the next- highest average color value is used to scale the amount of color accentuation applied to any pixel.
  • This difference between the highest and next-highest average color values are inputs to a mathematical function, which then creates a color prominence multiplier. This is implemented by multiplying the result of the average-value difference function by the resulting scaling function for that pixel. It is applied only to those pixels where the maximum color component for the pixel is the same color component as the maximum average color component of the image.
  • %MAXnew %MAX + f(%MAX - %MID) * g(ANGmax - ANGmid)
  • ANGmax is the averaged color component value across all pixels in an image that has the largest resulting value
  • ANGmid is the averaged color component value across all pixels in an image that has the next-largest resulting value
  • g(ANGmax - ANGmid) is a function that calculates the amount of color prominence scaling that should be applied to an image when the MAXold color and ANGmax color are the same color component.
  • This adjustment for color dominance in a region can also be achieved using convolution.
  • a convolution is performed that integrates over all the neighboring pixels within some radius R, the cumulative sum of each magnitude of the same color component divided by their corresponding distances from the given pixel.
  • the scaling function applied to the given pixel is multiplied by a coefficient inversely proportional to the convolution result. In this manner, when a pixel resides within a region where the same maximum color component is heavily dominant, the scaling function is reduced in effect.
  • similar convolution results can be achieved by using the distance to some power, or the color component magnitude to some power or some combination thereof.
  • the scaling functions can be applied such that a different scaling function is applied depending on which color component is the MAX (in the case of an additive color space) or MIN (in the case of a subtractive color space).
  • each color can have a different scaling function for the same differences. This is another way of dealing with the over saturation problem in at least some colors. For example, often R is accentuated too much, while the G and B are acceptable when all three use the same scaling function.
  • each color component can have its own scaling function such that when a given pixel has a color component selected as MAX (in the additive case), then the scaling function for that color is used for that pixel.
  • the R scaling function is less than the scaling function for G and B.
  • the selection and shape of the scaling functions for the different color components will depend on the characteristics or requirements of the particular display or image output device, storage device or where the color coding and decoding signal process is situated.
  • a particular display or printing device may have particular visual characteristics, in other words, its color response function may have nonlinear aspects. Therefore, the scaling function can be modified to complement these effects. For example, where the display device would appear to over saturate at certain levels when color accentuation is applied, the scaling function can be modified to level off when %MLD-%MIN (in a subtractive space) reaches a certain threshold and roll-off when it reaches a second threshold. Similarly, when %MLD- %MLN is less than a certain threshold, the scaling function can be set to a set amount. Practitioners of ordinary skill in the art can construct smooth transitions from the scaling function domain across the threshold to the domains where the scaling function value is set to a different function.
  • the present system is considered a color accentuation system, not a color correction system, although it is expected that this process can become a new kind of color correction.
  • Color correction implies that the to be printed or displayed color is corrected to be identical to the original image. In many cases, the image taken has color flaws that depart from the original, or the intended original.
  • the present method or system has used the amplitude of the color components as the parameter to be measured and adjusted.
  • Other parameters of the system may be used for the relative measures and adjustment. They could include any of color, hue, saturation, luminance, chrominance, focus or any other video control.
  • the scaling function, adjustments and compensation may use functions whose arguments do not include the differences of color component magnitudes.

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  • Physics & Mathematics (AREA)
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Abstract

Le procédé d'accentuation de couleurs selon la présente invention permet de déterminer l'intensité relative de chaque composante de couleur dans chaque pixel ou zone. Ledit procédé permet de sélectionner et d'ajuster l'intensité d'une ou de plusieurs des couleurs en fonction des intensités relatives déterminées de chaque composante de couleur. Le type et la quantité de l'ajustement peut dépendre des différences d'intensité relatives. Une ou plusieurs des intensités sont ajustées pour changer les intensités relatives. Généralement, la différence dans un espace colorimétrique soustractif se situe entre l'intensité de couleur la plus faible et l'intensité de couleur moyenne et dans un espace colorimétrique additif, elle se situe entre l'intensité de couleur la plus élevée et l'intensité de couleur moyenne. Généralement, la composante de couleur la plus faible est réduite dans l'espace colorimétrique soustractif et la plus élevée est augmentée dans l'espace colorimétrique additif. Plusieurs fonctions de mise à l'échelle et plusieurs compensations ou ajustements différents de l'accentuation de couleurs peuvent être utilisés.
EP03749058A 2002-08-19 2003-08-18 Procede d'accentuation de couleurs Withdrawn EP1532580A2 (fr)

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US40415602P 2002-08-19 2002-08-19
US404156P 2002-08-19
US41354402P 2002-09-26 2002-09-26
US413544P 2002-09-26
US41819002P 2002-10-15 2002-10-15
US418190P 2002-10-15
PCT/US2003/025692 WO2004017261A2 (fr) 2002-08-19 2003-08-18 Procede d'accentuation de couleurs

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US7605959B2 (en) * 2005-01-05 2009-10-20 The Ackley Martinez Company System and method of color image transformation
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WO2004017261A2 (fr) 2004-02-26
TW200416618A (en) 2004-09-01

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