KR102511039B1 - Image processing method, image processing circuit and display device using the same - Google Patents

Abstract

According to the present invention, the image processing technology analyzes the luminance distribution of the input HDR image and adaptively determines the roll-off point, luminance correction constant, and color difference correction constant to convert the luminance component of the input HDR image into a luminance suitable for the gamma characteristics of the display device. In addition to converting into components, pixels corresponding to the roll-off period correct color difference components using color difference correction constants to prevent color shift (Hugh shift) and to mitigate local oversaturation in high luminance pixels, thereby improving image quality. degradation can be minimized.

Description

Image processing method, image processing circuit and display device using the same

The present invention relates to a display device, and more particularly, to an image processing method and an image processing circuit capable of minimizing deterioration in image quality of an image having a wide luminance dynamic range and displaying the image on the display device, and a display device using the same.

It is known that in a real natural environment, humans can perceive a wide luminance dynamic range of about 10 ^-4 to 10 ⁸ cd/m ² , and high dynamic range (HDR) technology considering these cognitive characteristics interest in is growing. Until now, HDR technology has been mostly concentrated in the camera field, but has recently been expanded to include video production and display device development.

However, the luminance dynamic range that a current display device can express is considerably lower than that of HDR image content. For example, the peak luminance specification of the current HDR video is 10000 nit, but the peak luminance that the display device can express is 400 nit. is about

Therefore, in order to display HDR image content that is wider than the luminance range that can be displayed by the display device, an image processing algorithm that converts the HDR image content to fit the narrow luminance range of the display device, that is, the gamma characteristic, is required for the display device. An image processing technique capable of displaying on a display device by minimizing image quality deterioration such as color shift (hue shift) of the image is required.

The present invention provides an image processing method and circuit capable of displaying an HDR image on a display device by minimizing picture quality degradation, and a display device using the same.

An image processing method according to an embodiment of the present invention includes linearizing input image data having a high dynamic range (HDR) using a predetermined decoding function; converting the linearized image data into a luminance component and a chrominance component; determining a roll-off point of a luminance mapping function, a luminance correction constant, and a chrominance correction constant based on a result of analyzing the luminance distribution of the input image; correcting a luminance component of the input image data to a luminance component having a gamma characteristic of a display device using a luminance mapping function determined using the roll-off point and a luminance correction constant; correcting the chrominance component of pixels corresponding to a high roll-off period using the chrominance correction constant; converting the corrected luminance component and color difference component into corrected image data; and gamma-converting the corrected image data and outputting the corrected image data.

An image processing circuit according to an embodiment of the present invention includes a linearizer for linearizing HDR input image data using a predetermined decoding function, and a color space converter for converting the linearized image data into a luminance component and a chrominance component; a luminance analyzer for analyzing the luminance distribution of the input image and determining a roll-off point of a luminance mapping function, a luminance correction constant, and a chrominance correction constant based on the result; A luminance mapping unit correcting the luminance component of the input image data to a luminance component having a gamma characteristic of a display device using a luminance mapping function determined using the roll-off point and the luminance correction constant; a chrominance corrector for correcting the chrominance component of pixels corresponding to a roll-off period higher than luminance by using the chrominance correction constant; a color space inverse transform unit converting the corrected luminance component and color difference component into corrected image data; and a gamma conversion unit for gamma-converting the corrected image data and outputting the corrected image data.

A display device according to an embodiment of the present invention includes the above-described image processing circuit.

An image processing method and circuit according to an embodiment of the present invention and a display device using the same analyze a luminance distribution of an input HDR image and adaptively determine a roll-off point, a luminance correction constant, and a chrominance correction constant to obtain an image of an input HDR image. In addition to converting the luminance component into a luminance component suitable for the gamma characteristics of the display device, the pixels corresponding to the roll-off period correct the chrominance component using the chrominance correction constant to prevent color shift and color shift of the HDR image. Deterioration of image quality may be minimized by mitigating a phenomenon of local oversaturation in high luminance pixels.

1 is a diagram illustrating a color shift phenomenon due to mapping of a roll-off section when an HDR image is mapped according to a gamma curve of a display device by way of example.
2 is a flowchart illustrating an image processing method according to an embodiment of the present invention.
3 is a block diagram showing the configuration of an image processing circuit according to an embodiment of the present invention.
4 is a graph for explaining a luminance mapping method according to an embodiment of the present invention.
5 is a diagram showing color shift improvement results according to an image processing method according to an embodiment of the present invention.
6 is a schematic block diagram of an HDR display device having an image processing circuit according to an embodiment of the present invention.
FIG. 7 is an equivalent circuit diagram illustrating a configuration of an LCD subpixel applied to FIG. 6 .
FIG. 8 is an equivalent circuit diagram illustrating the configuration of an OLED sub-pixel applied to FIG. 6 .

Prior to the description of the embodiments of the present invention, the problems of the prior art related to the present invention will be first looked at.

1 is a graph (a) showing a comparison between a decoding curve of an HDR image and a gamma curve of a display device, and a diagram illustrating a Hugh shift result (b) due to mapping a roll-off section of an HDR image.

HDR video has recently been defined by the Society of Motion Picture and Television Engineers (SMPTE) ST. ) is gamma encoded using an encoding curve.

In order to display the PQ-encoded HDR image on a display device following the 2.2 gamma curve, the PQ decoding curve shown in FIG. A data mapping method using a look-up table (LUT), which converts grayscale data that follows a gamma curve of a display device, for example, grayscale data that follows a 2.2 gamma curve, is advantageous in terms of cost.

However, the maximum luminance specification for HDR video is 10000nit. On the other hand, the maximum luminance that the current display device can express is 400nit. Since the above-described data mapping is low, high-grayscale aggregation in which all high-grayscales exceeding 400 nit. in the HDR image are saturated with the maximum luminance (400 nit.) of the display device occurs.

In order to minimize such high grayscale saturation, the display device bends the PQ decoding curve based on a predetermined inflection point, that is, a roll-off point (RP) as shown in FIG. A roll-off processing method that adjusts the luminance of a high-grayscale region of a point or more to be dark overall while having grayscale expressiveness, or a clipping processing method that clips the maximum luminance of a display device is used.

For example, the roll-off processing method converts RGB data for each color channel using a conversion LUT following a gamma curve including a roll-off section as shown in FIG. Roll-off processing of grayscale data

However, when at least one of the RGB data is mapped and converted to the roll-off period, the input RGB ratio before roll-off and the output RGB ratio after roll-off become different. As a result, as shown in FIG. 1(b), a Hue shift artifact, that is, a color shift phenomenon in which colors are distorted occurs because Hue values representing colors are different before and after roll-off. There is a problem with

When the data of the roll-off point (RP) in FIG. 1 (a) is 151, G and B (154, 166) among the input PQ images R, G, and B (142, 154, 166) ) is mapped to the roll-off section and converted into output images R', G', B' (168, 200, 207), so that the input idle value (213°) and the output idle value (190°) are shifted, indicating that the color is distorted. can

In order to solve this problem, the present invention uses luminance information (Y) without using conversion LUT for each color channel, and performs PQ-to-gamma conversion adaptively by analyzing the luminance distribution of the input image without conversion LUT. Accordingly, an image processing method and circuit of a display device capable of suppressing a color shift phenomenon are proposed.

Hereinafter, preferred embodiments of the present invention will be described.

2 is a flowchart showing an image processing method step by step according to an embodiment of the present invention, FIG. 3 is a block diagram briefly showing the configuration of an image processing circuit according to an embodiment of the present invention, and FIG. It is a diagram showing a graph for PQ-to-gamma mapping of luminance information (Y) according to an embodiment of the present invention.

Referring to FIGS. 2 and 3 , HDR images (R, G, and B) are received from the input unit 10 and supplied to the PQ linearization unit 20 . (S21).

The PQ linearization unit 20 converts the HDR images (R, G, and B) supplied from the input unit 10 into inverse gamma using a PQ decoding curve (function) having an inverse functional relationship with the PQ encoding curve (function) of the HDR image. By correcting, an HDR image (R', G', B') in which a luminance relationship for each gray level is linearized is output. (S22)

The color space conversion unit 30 generates linearized HDR images (R', G', B') using a predetermined color space conversion function (RGB-to-YCbCr) or a color space conversion LUT determined by applying the function. is converted into a luminance component (Y) and color difference components (Cb, Cr). (S23) The color difference component (Cb) converts the difference (Y-B) between the luminance component (Y) and the blue component (B) into a color difference signal (Cr). denotes a difference (Y-R) between the luminance component (Y) and the red component (R).

The luminance analysis unit 40 analyzes the luminance distribution of the input PQ image at least in units of frames to determine a roll-off point, a luminance correction constant, and a chrominance correction constant. (S24)

The luminance mapping unit 50 determines the Y PQ-to-gamma mapping function (graph) shown in FIG. 3 using the roll-off point and the luminance correction constant supplied from the luminance analysis unit 40, and the determined Y PQ Using the -to-gamma mapping function, the luminance component (Y_PQ) of the PQ image is mapped to the luminance component (Y_2.2) of the display device and output. (S25)

The color difference correcting unit 60 detects corresponding pixels whose pixel luminance is higher than the luminance at the roll-off point, and uses the luminance correction constant and color difference correction constant supplied from the luminance analyzer 40 only for the detected pixels. to correct the color difference components (Cb, Cr). (S26)

The color space inverse transform unit 70 uses a predetermined color space inverse transform function (YCbCr-to-RGB) or a predetermined color space inverse transform LUT by applying this function, and the luminance component (Y ') and color difference components (Cb, 'Cr') are converted into R', G', B' images and output. (S27)

The gamma conversion unit 80 nonlinearizes R', G', and B' images supplied from the color space inverse conversion unit 70 using a gamma conversion LUT, and outputs nonlinearized Ro, Go, and Bo images. (S28)

A detailed description of the aforementioned luminance analyzer 40, luminance mapping unit 50, and color difference corrector 60 is as follows.

For PQ-to-gamma mapping, the luminance component (Y) is replaced with a Y value (luminance normalization value) between 0 and 1. HDR video encoded with PQ (hereafter referred to as PQ video) is 0 to 10000 nit. The luminance information in the range is substituted with Y values of 0 to 1, and the display device with the maximum luminance of 400 nit. is 0 to 400 nit. Luminance information in the range is also replaced with Y_2.2 values between 0 and 1.

At this time, since the Y value of the PQ image and the absolute value of the Y_2.2 value of the display device are different as the luminance range of the PQ image and the display device are different, Y of the PQ image substituted between 0 and 1 as shown in Equation 1 below Y_PQ of the Y mapping function shown in FIG. decide

<Equation 1>

For example, when the maximum luminance of the PQ image (Max.PQ Luminance) is 10000 nit and the maximum luminance of the display device (Max.Display Liminance) is 400 nit, the correction constant (10000/400 = 25) is calculated as in Equation 1 above and multiplied by the initial Y value, the initial Y value of “1” of the input PQ image is determined as the Y_PQ value of 25.

The luminance analyzer 40 analyzes the luminance distribution of the input PQ image to determine the roll-off point RP at which the roll-off section starts in the Y mapping graph shown in FIG. 3 . In order to determine the roll-off point (RP), the luminance distribution that is equal to or greater than the maximum luminance (Max.Display Liminance) of the display device in the input PQ image is analyzed to determine the roll-off point (RP = Rolloff Point) as shown in Equation 2 below. do.

<Equation 2>

The luminance analyzer 40 determines the ratio (Over Max. Display Luminance) of “Pixels_Over Max.Display Luminace” to “All Pixels” in each frame of the input PQ image. Ratio) and the calculation result of "1 - Over Max. Display Luminance Ratio" determines the rolloff point. The roll-off point is set closer to “0” if the number of high-brightness pixels equal to or greater than the maximum luminance of the display device is large, and set closer to “1” in the opposite case.

For example, when the ratio of the number of pixels of 400 nit or more, which is the maximum luminance of the display device, to the total number of pixels in each frame is 30%, the roll-off point is determined as "1 - 0.3 = 0.7".

Then, based on the result of analyzing the luminance distribution described above, the luminance analyzer 40 determines which part of Y_PQ (0 to 25) from the roll-off point in FIG. 3 is to be mapped to the remaining gradations (1-Y_R). Decide. Mapping up to Y_PQ 25 in FIG. 3 is the best way to express all information of the original image, but since the amount of gradation remaining from the roll-off point (RP) is not large, it is impossible to express in an actual display device. Therefore, the luminance analyzer 40 calculates the luminance correction constant α_Y based on the analysis result of the luminance distribution described above, and multiplies Y_2.2 by the luminance correction constant α_Y as shown in Equation 3 below to obtain an upper limit value of Y(PQ) “Y_PQ”. Pos" is determined.

<Equation 3>

The luminance analyzer 40 detects a luminance point at which the luminance correction constant α_Y in Equation 3 is 3% or less of a threshold value based on the luminance distribution analysis results shown in Table 1 below, and “maximum luminance of the display device (Max. .Display Liminance)” is calculated as the luminance correction constant α_Y.

1st video 2nd video 400 nits or more = 30% Over 400 nits = 18% 1200 nits or more = 23% 800 nits or more = 12% 2000nit or more = 12% 1200nit or more = 3% 2800 nit or more = 3%

For example, when 2800 nit is detected as a luminance point that is below the threshold value of 3% in the first image from the luminance distribution analysis results as shown in Table 1, the luminance correction constant α_Y = 2800/400 = 7 is calculated, and the above math According to Equation 3, the Y_PQ upper limit value "Y_PQ Pos" of the roll-off section is determined as "Y_PQ Pos = 7", which is the result of multiplying the Y_2.2 maximum value "1" by the luminance correction constant α_Y = 7.

In Table 1, when 1200 nit is detected as the luminance point below the threshold 3% in the second image, the luminance correction constant α_Y = 1200/400 = 3 is calculated, and Y (PQ) upper limit value " Y_PQ Pos" is determined as "Y_PQ Pos = 3", which is the result of multiplying the Y_2.2 maximum value "1" by the luminance correction constant α_Y=3.

Here, when the value of Y_2.2 is “1”, the luminance correction constant α_Y is immediately determined as the Y(PQ) upper limit value “Y_PQ Pos”.

Next, the luminance analyzer 40 converts the chrominance correction constants α_Cb,Cr for correcting the chrominance components (Cb and Cr) of the pixels included in the roll-off section to the luminance correction constants as shown in Equation 4 below. Decide by considering α_Y

<Equation 4>

The luminance analyzer 40 detects corresponding pixels whose pixel luminance (Luminance_Pixel) is higher than the luminance (Luminance_Rolloffpoint) at the roll-off point.

The luminance analyzer 40 calculates the ratio of “−0.5” to “the result of multiplying the maximum luminance of the display device (Max.Display Liminance) by the luminance correction constant (α_Y)”, Calculate the difference in luminance (Luminance_Rolloffpoint) at the off point, multiply the former calculated value with the latter calculated value, and then add a constant of “1” to determine the color difference correction constant α_Cb,Cr in the range of -0.5 to 0.5 . As the luminance of the corresponding pixel is higher than the luminance at the roll-off point, the chrominance correction constant α_Cb,Cr increases, and as the luminance decreases, the chrominance correction constant α_Cb,Cr decreases.

In this way, the roll-off point (RP) and the Y(PQ) upper limit value "Y_PQ Pos" are determined according to the luminance distribution of the input image in the luminance analysis unit 40 as shown in FIG. 4, so that the luminance mapping unit 50 Graphs 1 and 2 for PQ-to-gamma mapping of luminance information (Y) are determined.

The luminance mapping unit 50 maps the luminance component (Y_PQ) of the input PQ image to the luminance component (Y_2.2) of the display device using the mapping graph (function) of the luminance component (Y) shown in FIG. do.

The color difference correcting unit 60 uses the color difference correction constants α_Cb,Cr supplied from the luminance analyzer 40 only for corresponding pixels whose pixel luminance (Luminance_Pixel) is higher than the luminance at the roll-off point (Luminance_Rolloffpoint). As shown in Equation 4, the color difference components (Cb, Cr) are corrected. Accordingly, in pixels higher than the luminance (Luminance_Rolloffpoint) at the roll-off point, only saturation is reduced while maintaining the rest value (H), so that oversaturation can be alleviated.

As described above, the image processing method and circuit according to an embodiment of the present invention determines the roll-off point, luminance correction constant, color difference correction constant, etc. based on the result of analyzing the luminance distribution of the input PQ image to determine the luminance component of the PQ image. (Y_PQ) is mapped to the luminance component (Y_2.2) of the display device, and pixels with luminance higher than the roll-off point are further corrected for the chrominance components (Cb, Cr) using a chrominance correction constant, so that the rest value (H) It is possible to prevent a color shift phenomenon and alleviate an oversaturation phenomenon by reducing only saturation while maintaining a color shift, thereby improving image quality.

5 is a diagram showing the result of the Hugh shift improvement according to the image processing method according to the present invention.

Referring to FIG. 5(a), the input PQ images R, G, and B (142, 154, 166) are affected by roll-off processing based on the existing RGB roll-off point 151, and output R' . .

Referring to FIG. 5(b), the input PQ images R, G, and B (166, 151, 146) are affected by roll-off processing based on the existing RGB roll-off point 151, and output R' . .

Referring to FIG. 5(c), since the input PQ images R, G, and B (137, 122, 61) are not affected by the roll-off process based on the existing RGB roll-off point 151, the output R′ , G', B' is converted into (154, 118, 33), the rest value (44 °) is maintained, and converted into output Ro, Go, Bo (154, 119, 33) through the above-described image processing technology of the present invention It can be seen that the dormant value (44°) is maintained and no color shift occurs.

The above-described image processing circuit and method of the present invention can be applied to both a liquid crystal display device and an organic light emitting diode display device.

6 is a block diagram schematically showing the configuration of an HDR display device according to an embodiment of the present invention, FIG. 7 is a configuration of an LCD subpixel applied to the display panel of FIG. 6, and FIG. 8 is a configuration of the display panel of FIG. It is an equivalent circuit diagram illustrating the configuration of an applied OLED sub-pixel.

The display device shown in FIG. 6 includes a timing controller 100, a data driver 200 and a gate driver 300 as a panel driver, a display panel 400, and a gamma voltage generator 500.

The display panel 400 displays an image through a pixel array in which pixels are arranged in a matrix form. Each pixel of the pixel array is composed of R (Red), G (Green), and B (Blue) subpixels (SP), and may additionally include a W (White) subpixel to improve luminance. A liquid crystal display (LCD), an organic light emitting diode (OLED) display, an electrophoretic display (EPD), or the like may be used as the display panel 400 .

For example, when the display panel 400 is an LCD panel, as shown in FIG. 7 , each subpixel SP includes a thin film transistor (TFT) connected to a gate line (GL) and a data line (DL), and a thin film. A liquid crystal capacitor Clc and a storage capacitor Cst are connected in parallel between the transistor TFT and the common electrode. The liquid crystal capacitor (Clc) charges the difference voltage between the data signal supplied to the pixel electrode and the common voltage (Vcom) supplied to the common electrode through the thin film transistor (TFT), and drives the liquid crystal according to the charged voltage to determine the amount of light transmittance. to control The storage capacitor Cst stably maintains the voltage charged in the liquid crystal capacitor Clc.

In contrast, when the display panel 400 is an OLED panel, as shown in FIG. 8 , each subpixel SP includes an OLED element connected between a high potential power supply (EVDD) line and a low potential power supply (EVSS) line. , and a pixel circuit including first and second switching TFTs (ST1, ST2), a driving TFT (DT), and a storage capacitor (Cst) to independently drive the OLED element, and the pixel circuit configuration is various, so FIG. 8 is not limited to the structure of

The OLED element includes an anode connected to the driving TFT (DT), a cathode connected to the low potential voltage (EVSS), and a light emitting layer between the anode and the cathode, and emits light proportional to the amount of current supplied from the driving TFT (DT). Occurs.

The first switching TFT (ST1) is driven by the gate signal of one gate line (GLa) to supply the data voltage from the corresponding data line (DL) to the gate node of the driving TFT (DT), and the second switching TFT (ST2) ) is driven by a gate signal of another gate line GLb to supply a reference voltage from the reference line RL to the source node of the driving TFT DT. The second switching TFT (ST2) is further used as a path for outputting the current from the driving TFT (DT) to the reference line (R) in the sensing mode.

The storage capacitor Cst connected between the gate node and the source node of the driving TFT DT transmits the data voltage supplied to the gate node through the first switching TFT ST1 and the source node through the second switching TFT ST2. The differential voltage of the reference voltage supplied to is charged and supplied as the driving voltage of the driving TFT (DT).

The driving TFT DT controls the current supplied from the high-potential power supply EVDD according to the driving voltage supplied from the storage capacitor Cst, thereby supplying a current proportional to the driving voltage to the OLED element so that the OLED element emits light.

The data driver 200 receives the data control signal DCS and image data VD from the timing controller 100 . The data driver 200 is driven according to the data control signal DCS to subdivide the reference gamma voltage set supplied from the gamma voltage generator 500 into grayscale voltages respectively corresponding to the grayscale values of the data, and then subdivided into grayscale voltages. Each of the digital image data VD is converted into an analog data signal using grayscale voltages, and the analog data signal is supplied to the data lines of the display panel 400, respectively.

The data driver 200 is composed of a plurality of data drive ICs that divide and drive the data lines of the display panel 400, and each data drive IC is TCP (Tape Carrier Package), COF (Chip On Film), FPC (Flexible Print) It may be mounted on a circuit film such as a circuit film and attached to the display panel 400 using a Tape Automatic Bonding (TAB) method or mounted on the display panel 400 using a Chip On Glass (COG) method.

The gate driver 300 drives a plurality of gate lines of the display panel 400 respectively using the gate control signal GCS supplied from the timing controller 100 . The gate driver 300 supplies a scan pulse of a gate-on voltage to each gate line in a corresponding scan period in response to a gate control signal, and supplies a gate-off voltage in the remaining period. The gate driver 300 may receive the gate control signal GCS from the timing controller 100 or the gate control signal GCS from the timing controller 100 via the data driver 200 . The gate driver 300 is composed of at least one gate IC, mounted on a circuit film such as TCP, COF, FPC, etc., and attached to the display panel 400 in a TAB method or mounted on the display panel 400 in a COG method. can Unlike this, the gate driver 300 is a GIP (Gate In Panel) type embedded in the non-display area of the display panel 400 by being formed on a thin film transistor substrate together with the thin film transistor array constituting the pixel array of the display panel 400 . can be provided with

The timing controller 100 receives HDR images, that is, PQ image data and timing signals from an external host system. For example, the external host system may be any one of a computer, a TV system, a set-top box, a portable terminal system such as a tablet or mobile phone.

The timing controller 100 controls driving timings of the data driver 200 and the gate driver 300 respectively using the input timing signals, converts the PQ image data to match the gamma characteristics of the display device, and converts the data driver 200 output as

To this end, the timing controller 100 includes a control signal generator 110 and an image processing circuit 120 . Meanwhile, the image processing circuit 120 may be provided as a separate IC, separated from the timing controller 100, and may be located at a previous stage of the timing controller 100.

The control signal generator 110 generates a data control signal and a gate control signal using the input timing signals and outputs them to the data driver 200 and the gate driver 300, respectively. Timing signals received by the control signal generator 110 include a dot clock, a data enable signal, a vertical synchronization signal, and a horizontal synchronization signal, but the vertical synchronization signal and the horizontal synchronization signal may be omitted. When the vertical synchronizing signal and the horizontal synchronizing signal are omitted, the control signal generator 110 may generate and use the vertical synchronizing signal and the horizontal synchronizing signal by counting the data enable signal according to the dot clock. The data control signals may include a source start pulse, a source sampling clock, a polarity control signal, and a source output enable signal for controlling driving of the data driver 200 . The gate control signals may include a gate start pulse, a gate shift clock, and a gate output enable signal for controlling driving of the gate driver 300 .

The image processing technology described above with reference to FIGS. 2 to 4 is applied to the image processing circuit 120 . The image processing circuit 120 linearizes the input PQ image (RGB), converts it into a luminance component (Y) and chrominance components (Cb, Cr), and rolls off based on the result of analyzing the luminance distribution of the input PQ image. The luminance component (Y_PQ) of the PQ image is mapped to the luminance component (Y_2.2) of the display device by determining the point, luminance correction constant, chrominance correction constant, etc. By further compensating the color difference components (Cb, Cr) using the color difference components (Cb, Cr), only the saturation (Saturation) is reduced while maintaining the rest value (H) to prevent a color shift phenomenon and to alleviate an oversaturation phenomenon, thereby improving image quality. The image processing circuit 120 inversely transforms the corrected luminance component (Y') and chrominance components (Cb', Cr') into R'G'B data, and then non-linearizes the corrected luminance component (Y') and chrominance components (Cb', Cr') and outputs the result to the data driver 200.

The image processing circuit 120 may further perform necessary image processing such as reducing power consumption, compensating for image quality, or compensating for degradation, and then output the image to the data driver 200 .

For example, in the HDR display device according to the prior art, the skin color is changed by the roll-off process of the high gradation region, resulting in a hue shift phenomenon that looks yellowish, but the HDR display according to the embodiment of the present invention The device can maintain the hue of the skin color without distortion through the above-described image processing.

As described above, the image processing method and circuit according to an embodiment of the present invention and the display device using the same analyze the luminance distribution of the input HDR image to adaptively determine the roll-off point, luminance correction constant, and color difference correction constant, and then input the input HDR image. The luminance component of the HDR image is converted into a luminance component suitable for the gamma characteristics of the display device, and the pixels corresponding to the roll-off period correct the chrominance component using a chrominance correction constant to prevent color shift and color shift of the HDR image. In addition, it is possible to minimize image quality deterioration by mitigating a phenomenon of local oversaturation in high luminance pixels.

Through the above description, those skilled in the art will understand that various changes and modifications are possible without departing from the spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims.

10: video input unit 20: PQ linearization unit
30: color space conversion unit 40: luminance analysis unit
50: luminance mapping unit 60: color difference correction unit
59: color space inverse conversion unit 70: gamma conversion unit
110: control signal generator 120: image processing circuit
100: timing controller 200: data driver
300: gate driver 400: display panel
500: gamma voltage generator

Claims (11)

linearizing input image data having a high dynamic range (HDR) using a predetermined decoding function;
converting the linearized image data into a luminance component and a chrominance component;
determining a roll-off point of a luminance mapping function, a luminance correction constant, and a chrominance correction constant based on a result of analyzing the luminance distribution of the input image;
correcting a luminance component of the input image data to a luminance component having a gamma characteristic of a display device using a luminance mapping function determined using the roll-off point and the luminance correction constant;
correcting the chrominance component of pixels corresponding to a roll-off section higher than the luminance of the roll-off point by using the chrominance correction constant;
converting the corrected luminance component and color difference component into corrected image data;
Gamma-converting the corrected image data and outputting the corrected image data;
The image processing method of claim 1 , wherein the corrected image data is converted into a form in which a rest value relative to the input image data is maintained and saturation is reduced. The method of claim 1,
Analyzing the luminance distribution of the input image data on a frame-by-frame basis;
The image processing method of claim 1 , wherein a ratio of the number of pixels having a maximum luminance or higher of the display device to the total number of pixels is calculated, and a result obtained by subtracting the calculated ratio from 1 is determined as the roll-off point. The method of claim 2,
Detecting a luminance point that is below a threshold value based on the analysis result of the luminance distribution;
determining a ratio of a luminance point that is less than or equal to the threshold value to a maximum luminance of the display device as the luminance correction constant;
An image processing method of determining an upper limit value of a luminance component of the input image to be mapped to the luminance mapping function using the luminance correction constant. The method of claim 1,
A ratio of -0.5 to a value obtained by multiplying the maximum luminance of the display device by the luminance correction constant is calculated as a first value, a difference between pixel luminance and luminance at a roll-off point is calculated as a second value, and the An image processing method for determining the color difference correction constant through an operation of multiplying 1 and a second value and then adding a constant of 1. A linearizer for linearizing HDR input image data using a predetermined decoding function;
a color space converter for converting the linearized image data into a luminance component and a chrominance component;
a luminance analyzer for analyzing the luminance distribution of the input image and determining a roll-off point of a luminance mapping function, a luminance correction constant, and a chrominance correction constant based on the result;
a luminance mapping unit correcting a luminance component of the input image data to a luminance component having a gamma characteristic of a display device using a luminance mapping function determined using the roll-off point and the luminance correction constant;
a chrominance corrector for correcting the chrominance component of the pixels corresponding to the roll-off section having a higher luminance than the luminance of the roll-off point by using the chrominance correction constant;
a color space inverse transform unit converting the corrected luminance component and color difference component into corrected image data;
a gamma conversion unit for gamma-converting the corrected image data and outputting the corrected image data;
The image processing circuit for converting the corrected image data into a form in which a rest value compared to the input image data is maintained and saturation is reduced. The method of claim 5,
The luminance analyzer
Analyzing the luminance distribution of the input image data on a frame-by-frame basis;
An image processing circuit for calculating a ratio of the number of pixels having a maximum luminance or higher of the display device to the total number of pixels, and determining a result obtained by subtracting the calculated ratio from 1 as the roll-off point. The method of claim 6,
The luminance analyzer
Detecting a luminance point that is below a threshold value based on the analysis result of the luminance distribution;
determining a ratio of a luminance point that is less than or equal to the threshold value to a maximum luminance of the display device as the luminance correction constant;
An image processing circuit for determining an upper limit value of a luminance component of the input image to be mapped to the luminance mapping function using the luminance correction constant. The method of claim 5,
The luminance analyzer
A ratio of -0.5 to a value obtained by multiplying the maximum luminance of the display device by the luminance correction constant is calculated as a first value, a difference between pixel luminance and luminance at a roll-off point is calculated as a second value, and the An image processing circuit that determines the color difference correction constant through an operation of multiplying 1 and a second value and then adding a constant of 1. a display panel;
The image processing circuit according to any one of claims 5 to 8;
a panel driver for displaying the image supplied from the image processing circuit on the display panel;
A timing controller controlling driving timing of the panel driver;
The image processing circuit is built into the timing controller, is located between the timing controller and the panel driving unit, or is located in front of the timing controller. The method of claim 4,
wherein the chrominance correction constant increases as the luminance of the pixel is higher than the luminance at the roll-off point, and decreases as the luminance of the pixel decreases. The method of claim 8,
wherein the chrominance correction constant increases as the luminance of the pixel is higher than the luminance at the roll-off point, and decreases as the luminance of the pixel decreases.

Images