TWI780634B - Image calibration method of image system - Google Patents

Abstract

An image calibration method for use in an image system. The image system includes a projection device, a color detector and a processor. The image calibration method includes in an ambient light environment, the color detector measuring a background luminance and an ambient measurement of a test image on a projection surface, and the processor generating a color appearance representation using the background luminance and the ambient measurement; in a darkroom environment, the color detector measuring a darkroom measurement of a test image, and if a surround ratio is less than a predetermined threshold, the processor generating a target using the darkroom measurement and the color appearance representation; and the processor configuring a gamut of the projection device according to the target, and adjusting an image according to the gamut and the darkroom measurement, and the projection device projecting the adjusted image.

Description

Image Correction Method for Image System

The present invention relates to image processing, in particular to an image correction method for an image system that maintains color appearance consistency.

A projector is an optical device used to project images onto a screen. The projected image of the conventional projector is affected by the ambient light, causing the image color to be inconsistent with the color appearance in the darkroom under the ambient light.

At present, most projectors are aimed at the hardware structure of the projector, but seldom corrected for the visual experience of the user's environment. Therefore, there is a need for a projector that can maintain the consistency of color appearance under different ambient lights so that the user's Visual perception is not affected by ambient light sources.

An embodiment of the present invention provides an image correction method of an image system. The image system includes a projection device, a color sensor and a processor. The image correction method includes setting the projection device to project a test image onto the projection surface using a first color gamut under ambient light, the test image includes black, white and at least one specific color, and under the ambient light, the color sensing A set of ambient light measurements for black, a set of ambient light measurements for white, and at least one set of ambient light measurements for at least one specific color of the test image on the surface of the device, the processor based on the set of ambient light measurements for black , the set of ambient light measurements for white, at least one set of ambient light measurements for at least one specific color, the ambient light adaptability area luminance, the ambient light background luminance, and a set of ambient light surround parameters to generate a set of color appearances for black Indicates a value, a set of colors of white Appearance representation value and at least one set of color appearance representation values of at least one specific color. In a dark room, a projection device projects a test image onto a surface. Under a dark room, a color sensor measures a set of whiteness of the test image on the surface. A set of darkroom measurements of measured values and black, if the surround ratio is less than a predetermined threshold value, the processor based on at least one set of color appearance representation values of at least one specific color, the set of darkroom measurements of white, and the adaptive area brightness of the darkroom , dark room background brightness and a set of dark room surrounding parameters to generate at least one set of target values of at least one specific color, the processor sets the projection device to the second color gamut and the first color gamut according to at least one set of target values of at least one specific color Different from the second color gamut, the processor converts a set of color values of pixels in the original image according to the second color gamut to generate a set of converted color values. The set of converted color values includes the first color component value, the second The second color component value and the third color component value, the processor adds the brightness of the black color appearance representation value to the first color component value, the second color component value and the third color component value to generate the adjusted first color component value respectively. The color component value, the adjusted second color component value and the adjusted third color component value; and in a dark room, the projection device projects the adjusted first color component value, the adjusted second color component value and the adjusted The value of the third color component.

An embodiment of the present invention provides another image correction method for an image system. The image system includes a projection device, a color sensor and a processor. The image correction method includes setting the projection device to use the first color gamut to project a test image onto the surface under ambient light. The test image includes black and white. Under ambient light, the color sensor measures the black of the test image on the surface The group of measured values of ambient light for white and the group of measured values of ambient light for white, the processor bases the group of measured values of ambient light for black, the group of measured values of ambient light for white, the brightness of the adaptable area of ambient light, and the brightness of the background of ambient light and a set of ambient light surround parameters to generate a set of color appearance representation values for black. The processor converts a set of color values of pixels in the original image according to the second color gamut to generate a set of transformed color values. The converted color value includes the first color component value, the second color component value and the third color component value. Color component values to generate adjustments separately The adjusted first color component value, the adjusted second color component value, and the adjusted third color component value, and in a dark room, the projection device projects the adjusted first color component value and the adjusted second color component value value and the adjusted value of the third color component. If the first color component value is greater than the second color component value, the third color component value and the correction threshold value, the adjusted first color component value and the first color component value are positively correlated, and the adjusted second color component value and the first color component value are positively correlated. The two color component values are negatively correlated, and the adjusted third color component value is negatively correlated with the third color component value. If the first color component value is greater than the second color component value and the third color component value, but less than the correction threshold value, the adjusted first color component value and the gamma correction value of the first color component value are positively correlated, after adjustment The second color component value is negatively correlated with the gamma correction value of the second color component value, and the adjusted third color component value is negatively correlated with the gamma correction value of the third color component value.

1: Video system

10: Projection device

12: Color sensor

14: computer

140: Processor

16: Projection surface

30: Stimulus point

32: Proximal field

34: Background area

36: Surrounding area

Sd: measurement signal

Simg: video signal

200,600: image correction method

S202 to S224, S602 to S614: steps

50: The brightness distribution of the RGB color components of the original image

52: Brightness distribution of the maximum brightness component of the corrected image

54: Brightness distribution of the non-maximum brightness components of the corrected image

FIG. 1 is a block diagram of an imaging system in an embodiment of the present invention.

Fig. 2 is a flowchart of an image correction method of the image system in Fig. 1.

Fig. 3 is a schematic diagram of a measurement area of the image system in Fig. 1.

FIG. 4 shows a schematic diagram of an adjustment interface of the projection device in FIG. 1 .

Fig. 5 is a schematic diagram of the background brightness and gamma correction of an image in an embodiment of the present invention.

Fig. 6 is a flowchart of another image correction method of the image system in Fig. 1.

FIG. 1 is a block diagram of an imaging system 1 in an embodiment of the present invention. The image system 1 can maintain the consistency of the color appearance of the image without being affected by the ambient light, so that the color appearance under the ambient light is consistent with that in the darkroom.

The imaging system 1 includes a projection device 10 , a color sensor 12 , a computer 14 and a projection surface 16 . The computer 14 may include a processor 140 . The projection device 10 and the color sensor 12 can be coupled to the processor 140 through a universal serial bus (USB), RS-232 communication port interface or other communication interfaces. In some embodiments, the processor 140 can be located in the projection device 10 , and the computer 14 can be omitted from the imaging system 1 . The color sensor 12 can be a spectrophotometer or a spectrophotometer, such as screen color correction devices such as X-rite i1Pro2, i1Studio, and i1 Display Pro. The projection surface 16 can be a projection screen or a wall. There may be a predetermined distance between the color sensor 12 and the projection surface 16, for example, 40 cm.

The test environment of the imaging system 1 can be set as ambient light or a dark room. In ambient light, the light source can be natural light and/or artificial light. In a dark room, the light source is shaded or turned off. The processor 140 can transmit the image signal Simg to the projection device 10, and the projection device 10 can project the image onto the projection surface 16 according to the image signal Simg, and the color sensor 12 can measure the brightness of color components of different wavelengths in the projection surface 16 and the test environment To generate the measurement signal Sd, and send the measurement signal Sd to the processor 140, the processor 140 can correct the color gamut and/or perform contrast and saturation correction of the projection device 10 according to the measurement signal Sd, so as to maintain the consistent color appearance of the image sex.

FIG. 2 is a flow chart of an image correction method 200 of the image system 1, including steps S202 to S224, for maintaining the color appearance consistency of the image. Steps S202 to S208 are used to generate color appearance representation values under ambient light. Steps S210 to S218 are used to calibrate the color gamut of the projection device 10 . Steps S220 to S224 are used to correct the contrast and saturation of the image. Any reasonable technical changes or step adjustments fall within the scope of the disclosure of the present invention. Steps S202 to S224 are described below: Step S202: Under the ambient light, the color sensor 12 measures the background brightness Yb of the ambient light; Step S204: Under the ambient light, control the projection device 10 to project the test image onto the projection surface 16 using the first color gamut; Step S206: Under the ambient light, the color sensor 12 measures the blackness of the test image on the projection surface 16 A set of ambient light measurement values, a set of ambient light measurement values for white, and at least one set of ambient light measurement values for at least one specific color; step S208: the processor 140 is based on the set of ambient light measurement values for black, the set of ambient light measurement values for white A set of light measurements, at least one set of ambient light measurements for at least one specific color, an adaptive area luminance for ambient light, an ambient light background luminance, and a set of ambient light surround parameters to produce a set of color appearance representation values for black and one for white A set of color appearance representation values and at least one set of color appearance representation values of at least one specific color; step S210: in a dark room, control the projection device 10 to project a test image onto the projection surface 16; step S212: in a dark room, the color sensor 12 Measure a set of darkroom measurement values for white and a set of darkroom measurement values for black of the test image on the projection surface 16; step S214: the processor 140 determines whether the surround ratio Sr is smaller than a predetermined threshold Srth? If yes, continue to step S216; if not, end the image correction method 200.

Step S216: The processor 140 generates at least one specific color according to at least one set of color appearance representation values of at least one specific color, the set of darkroom measurement values of white, the brightness of the adaptable area of the dark room, the background brightness of the dark room, and a set of ambient parameters of the dark room at least one set of target values; step S218: the processor 140 sets the projection device 10 to the second color gamut according to at least one set of target values of at least one specific color; step S220: the processor 140 sets one of the pixels in the original image The set of color values is subjected to color gamut conversion according to the second color gamut to generate a set of converted color values, the set of converted color values includes the first color component value, the second color component value and the third color component value; Step S222: Processor 140 Add the brightness in the appearance value of the group of black colors to the first A color component value, a second color component value and a third color component value to generate an adjusted first color component value, an adjusted second color component value and an adjusted third color component value; step S224: In a dark room, the projection device 10 projects the adjusted first color component value, the adjusted second color component value, and the adjusted third color component value; the image correction method 200 ends.

In step S202 , the projection device 10 is turned off under ambient light, and the color sensor 12 measures the relative luminance on the projection surface 16 as the ambient light background luminance Yb. In some embodiments, the projection device 10 can also project the reference black onto the projection surface 16 under ambient light, and the color sensor 12 measures the brightness of the reference black on the projection surface 16 as the ambient light background brightness Yb. In some other embodiments, the color sensor 12 can also measure the brightness of the background area to generate the ambient background brightness Yb. FIG. 3 is a schematic diagram of a measurement area of the imaging system 1 , including a stimulus point 30 , a proximal field 32 , a background area 34 and a surrounding area 36 . The stimulus point 30 is the projection center of the projection device 10, the near-end field 32 is the range where the color sensor 12 expands 2% of the viewing angle from the center of the stimulus point 30, and the background area 34 is the color sensor 12 from the near-end field. The end field 32 expands outward to reach a range of 10% of the viewing angle, and the surrounding area 36 is the area where the color sensor 12 expands outward from the background area 34 . Since the ambient light will dominate the brightness of the reference black on the guide surface 16 and the background area 34 , the background brightness Yb of the ambient light obtained by the above three methods is substantially the same.

In step S204 , the first color gamut may be the maximum color gamut supported by the projection device 10 and greater than or equal to the Digital Cinema Initiatives (DCI)-P3 color gamut. The test image may include black, white and/or at least one specific color. At least one specific color includes all or a combination of the six axis colors. The six-axis colors include red, green, blue, cyan, magenta and yellow. Each color can be represented by red, green, blue, RGB (red, green, blue, RGB) components. For example, black (R,G,B) is (0,0,0), white (R,G,B) is (255,255,255), red (R,G,B) is (255,0,0) ), green (R, G, B) is (0,255,0), blue (R, G, B) is (0,0,255), cyan (R, G, B) is (0,255,255), foreign Red (R, G, B) is (255,0,255), and yellow (R,G,B) is (255,255,0). Since ambient light will cause the attenuation of the color gamut of the projection device 10, the color gamut of the projection device 10 is set to be greater than or equal to the DCI-P3 color gamut, so that the projection device 10 can be maintained as standard as possible under the influence of ambient light. The color gamut of standard red green blue (sRGB) does not reduce the color gamut of the projection device 10 to an unacceptable visual effect.

In step S206, each set of ambient light measurement values of a set of ambient light measurement values for black, a set of ambient light measurement values for white, and at least one set of ambient light measurement values for at least one specific color may be a tristimulus value (tri- stimulus), represented by the color appearance model (international commission on illumination, CIE) XYZ of the International Commission on Illumination. The set of ambient light measurement values for white can be regarded as the XYZ values of the reference white, and the Y value of the reference white can be regarded as the absolute luminance (absolute luminance) Lw of the reference white. For example, Table 1 shows the measured values XYZ of black, white, red, green, blue, cyan, magenta and yellow measured by the color sensor 12 under ambient light:

In step S208, the processor 140 converts each set of ambient light measurement values into a set of color appearance representation values according to a color appearance model (CAM), and the set of color appearance representation values may include lightness ( lightness, represented by J), red-green correlation dimension (a) and yellow-blue correlation dimension (b). The color appearance model can be CIECAM02 model, CIECAM16 model or other CIECAM models, and the conversion model of CIECAM16 can be expressed by formula (1): Jab=XYZCAM16UCS(XYZ,XYZw,La,Yb,surround) Formula (1)

Among them, Jab is a group of color appearance representation values; XYZ is the ambient light measurement value of a given color measured; XYZw is the ambient light measurement value of reference white; La is the brightness of the adaptable area; Yb is the background brightness ; and surround is the surround parameter, including the adaptability factor F, the surround influence parameter c and the color sensing factor Nc.

The adaptive area brightness La can be obtained by projecting the reference white color onto the projection surface 16 from the projection device 10 and directly measuring the absolute brightness of the reference white color at the stimulus point 30 on the projection surface 16 by the color sensor 12 . In some embodiments, the adaptive area brightness La can also be calculated according to the formula (2) by using the measured value of the reference white color. Formula (2) is as follows:

Among them, the La system is the brightness of the adaptability area; the Lw system is the absolute brightness of the reference white, the unit is cd/m ² ; the Ew system is the reference white illuminance, the unit is Lux, Ew=πLw; the Yb system is the background brightness; and the Yw system is the relative brightness of the reference white in the adaptability region.

In ambient light, the color sensor 12 measures the brightness on the projection surface 16 to obtain a suitable The relative brightness Yw of the reference white of the area. The processor 140 substitutes the absolute brightness Lw of the reference white, the background brightness Yb of the ambient light, and the relative brightness Yw of the reference white in the adaptability area into formula (2) to calculate the adaptability area brightness La of the ambient light.

The processor 140 calculates the surround ratio Sr. The surround ratio Sr can be expressed by formula (3): Sr=Lsw/Ldw formula (3)

where Sr is the surround ratio; Lsw is the absolute luminance of the projection surface of the surrounding area; and Ldw is the absolute luminance of white in the display area.

Formula (3) shows that the surround ratio Sr is the ratio of the absolute luminance Lsw of the projection surface of the surrounding area to the absolute luminance Ldw of white in the display area. In some embodiments, the ambient light background brightness Yb can be regarded as the absolute brightness Lsw of white in the surrounding area, the absolute brightness Lw of reference white can be regarded as the absolute brightness Ldw of white in the display area, and then the processor 140 calculates the ambient brightness according to formula (3). The surrounding ratio Sr of the light background luminance Yb and the relative luminance Lw of the reference white point. In some embodiments, the color sensor 12 can also measure the brightness of white on the projection surface 16 and the brightness of the surrounding area 36, and the processor 140 calculates the brightness of white on the projection surface 16 and the surrounding area according to formula (3) 36 brightness surround ratio Sr.

The processor 140 obtains surround parameters such as the adaptability factor F, the surround influence parameter c, and the color sensitivity factor Nc from Table 2 below according to the surround ratio Sr.

Table 2 shows the three environmental states defined by CIECAM16, which are average environment, bright room environment, and dark room. Each environmental state corresponds to its own adaptability factor F, surround influence parameter c, and color sensing factor Nc. For example, when the absolute brightness Lsw of the projection surface of the surrounding area is 10 nits, and the absolute brightness Ldw of the white color of the display area is 50 nits, the surround ratio Sr is 0.2 (=10/50), and the surround parameter surround includes the degree of adaptation The factor F is 0.9, the surround influence parameter c is 0.59 and the color sensitivity factor Nc is 0.95. The set of ambient light measurement values XYZ of the given color, the set of ambient light measurement values XYZw of the reference white color, and the ambient light background brightness Yb have been obtained in steps S202 and S206. A given color can be black, white, or any specific color. The processor 140 substitutes the set of ambient light measurement values XYZ of a given color, the set of ambient light measurement values XYZw of the reference white color, the ambient light adaptability area brightness La, the ambient light background brightness Yb, and the surround parameter surround into the formula (1) To calculate the set of color appearance representation value Jab of the given color. For example, the ambient light background brightness Yb can be 5.63, the ambient light adaptability area brightness La can be 13.41, and the Jab values of black, white, red, green, blue, cyan, magenta and yellow can be shown in Table 3:

In steps S210 and S212 , the ambient light source is turned off, and the image system 1 is in a dark room, the projection device 10 projects a test image onto the projection surface 16 , the test image includes black and/or white. Color sensor 12 measures a set of darkroom measurements for white of the test image on projection surface 16 to obtain an adaptive area luminance La of the darkroom, and a set of darkroom measurements for black of the test image on projection surface 16 to obtain Darkroom background brightness Yb. The set of darkroom measurements for white and the set of darkroom measurements for black can be expressed in CIE XYZ. The group of darkroom measurement values of white can be regarded as the XYZ values of the reference white, and the Y value of the reference white can be regarded as the absolute brightness Lw of the darkroom of the reference white.

In step S214, the processor 140 determines whether the surround ratio Sr is smaller than a predetermined threshold Srth. The predetermined critical value Srth may be 0.2. If the surround ratio Sr is less than the predetermined critical value Srth, the ambient state is ambient light or dark room, when the ambient state changes to other ambient light or dark room, the projection device 10 still has enough color gamut adjustment range to maintain the color appearance consistency, therefore The image correction method 200 continues to step S216. If the surround ratio Sr is greater than the predetermined critical value Srth, the environment state is an average environment. When the environment state changes to a dark room or ambient light, the color gamut adjustment range of the projection device 10 is not enough to maintain the color appearance consistency, so the image correction method 200 ends. .

In step S216, the processor 140 inversely converts each set of color appearance representation values generated in step S210 into a set of target values for the darkroom according to the color appearance model, and each set of target values can be represented by CIE XYZ. The inverse conversion model of CIECAM16 can be expressed by formula (4): XYZ=CAM16UCSXYZ(Jab,XYZw,La,Yb,surround) formula (4)

Among them, XYZ is a group of target values in the darkroom; Jab is a group of color appearance representation values; XYZw is the darkroom measurement value of reference white; La is the adaptive area brightness of the darkroom; Yb is the background brightness of the darkroom; and surround is the surrounding parameters of the darkroom, including the adaptability factor F, the surround influence parameter c and the color sensing factor Nc.

0)及顯示區域的白色的絕對亮度Ldw代入公式(3)以計算暗室環繞比率Sr(

0)，進而從表2獲得暗室環繞參數surround。暗室的可適性區域亮度La可在暗室下由色彩感測器12直接測量投影表面16中央區域之參考白色的絕對亮度而獲得。該組色外貌表示值Jab從步驟S208獲得，且可為黑色、白色或至少一特定色之一組色外貌表示值Jab。處理器140將該組色外貌表示值Jab、參考白色之暗室測量值XYZw、暗室的可適性區域亮度La、暗室背景亮度Yb及暗室環繞參數surround代入公式(4)以計算該組目標值XYZ。例如，例如，暗室背景亮度Yb可為0.13，暗室的可適性區域亮度La可為0.03，黑、白、紅、綠、藍、青、洋紅及黃色的目標值XYZ可如表4所示：

The absolute brightness Lsw of the projection surface surrounding the area may be the brightness measured by the color sensor 12 from the background area 34 and may be substantially equal to zero. The measured value Y of white in the dark room can be regarded as the absolute brightness Lw of the reference white in the dark room and the absolute brightness Ldw of white in the display area. The processor 140 calculates the absolute brightness Lsw(

0) and the absolute brightness Ldw of white in the display area are substituted into formula (3) to calculate the darkroom surround ratio Sr(

0), and then obtain the darkroom surround parameter surround from Table 2. The adaptive area luminance La of the dark room can be obtained by directly measuring the absolute luminance of the reference white in the central area of the projection surface 16 by the color sensor 12 in the dark room. The set of color appearance representation values Jab is obtained from step S208, and may be a set of color appearance representation values Jab of black, white or at least one specific color. The processor 140 substitutes the set of color appearance representation value Jab, the darkroom measurement value XYZw of the reference white color, the darkroom adaptability area luminance La, the darkroom background luminance Yb, and the darkroom surround parameter surround into formula (4) to calculate the set of target values XYZ. For example, for example, the background brightness Yb of the dark room can be 0.13, the adaptive area brightness La of the dark room can be 0.03, and the target values XYZ of black, white, red, green, blue, cyan, magenta and yellow can be as shown in Table 4:

In step S218 , the processor 140 adjusts at least one color temperature gain, at least one hue, and at least one saturation of at least one specific color according to at least one set of target values of at least one specific color to set the projection device 10 to the second color gamut. In some embodiments, the range of the second color gamut is smaller than that of the first color gamut. In some embodiments, the user can input a set of adjustment values according to at least one set of target values of at least one specific color, and the processor 140 can receive the set of adjustment values and adjust at least one color temperature of at least one specific color according to the set of adjustment values Gain (gain), at least one hue (hue) and at least one saturation (saturation), the color sensor 12 can measure at least one set of updated measurement values of at least one specific color in real time, and the user can At least one set of target values and at least one set of updated measurement values are input with another set of adjustment values until at least one set of target values and at least one set of updated measurement values of at least one specific color match. FIG. 4 shows an adjustment interface of the projection device 10 for inputting a set of adjustment values of at least one specific color. In some other embodiments, the color sensor 12 can measure at least one set of updated measurement values of at least one specific color in real time, and the processor 140 can also measure at least one set of target values and at least one set of updated measurement values of at least one specific color Values automatically adjust at least one color temperature gain, at least one hue, and at least one saturation of at least one specific color until at least one set of target values and at least one set of updated measured values for at least one specific color match. In some embodiments, at least one specific color may include a six-axis color, and the processor 140 adjusts the six sets of color temperature gain, hue and saturation of the six-axis color according to the six sets of target values of the six-axis color to set the projection device 10 to the first Dichroic gamut. In some embodiments, the processor 140 may further adjust at least one brightness of at least one specific color to set the projection device 10 to the second color gamut.

In step S220, the set of converted color values can be a set of RGB converted color values, the first color component value can be a red component value, the second color component value can be a green component value and the third color component value can be blue Color component value.

In step S222 , the processor 140 performs bottom light (minimum brightness) correction and gamma correction (Gamma correction) on the set of RGB converted color values to correct contrast and saturation. Because under ambient light, the brightness of the image will increase and the contrast will decrease, so the processor 140 additionally performs bottom brightness and gamma correction on the set of RGB converted color values, so as to simulate the image brightness and contrast under ambient light in a dark room, Also increase saturation. FIG. 5 is a schematic diagram of bottom brightness and gamma correction performed by the processor 140, wherein the horizontal axis represents the 256-level luminance (luminance) Lin before adjustment, and the vertical axis represents the 256-level luminance Lout after adjustment. Curve 50 shows the brightness distribution of the RGB color components of the original image; curve 52 shows the brightness distribution of the maximum brightness component of the corrected image; curve 54 shows the brightness distribution of the non-maximum brightness components of the corrected image. The maximum brightness component may be a color component with maximum brightness among RGB color components, and the non-maximum brightness component may be a color component without maximum brightness among RGB color components. The maximum brightness component can be obtained by formula (5): Cmax=Max(Rin,Gin,Bin) formula (5)

Among them, Cmax is the maximum brightness component value; and Rin, Gin, Bin are the red, green and blue component values of the image pixel before adjustment respectively.

If the first color component value is greater than the second color component value and the third color component value, the first color component value corresponds to the color component with the maximum brightness, and the second color component value and the third color component value correspond to the color component without the maximum brightness . The input and output luminance distribution 50 of the RGB color components of the original image is linear, and the minimum output luminance is 0-level. When performing underlight correction, the processor 140 adds the black brightness component value Jb in the group of black color appearance representation values to the RGB color components to increase the brightness of the image. When performing gamma correction, if the color component value Cmax of the maximum brightness is less than the correction critical value Iref, the adjusted first color component value and the gamma correction value of the first color component value before adjustment are positively correlated, and the adjusted first color component value is positively correlated. The gamma correction value of the second color component value and the second color component value before adjustment is negatively correlated, and the third color component value after adjustment is negatively correlated with the gamma correction value of the third color component value before adjustment, by the formula ( 6), (7), (8) means: Rout=((255-Cmax)/255*Jb)+(Rin/255) ^γ *(255-(255-Cmax)/255*Jb) formula (6)

Gout=((255-Cmax)/255*Jb)+(Gin/255) ^γ *(255-(255-Cmax)/255*Jb) formula (7)

Bout=((255-Cmax)/255*Jb)+(Bin/255) ^γ *(255-(255-Cmax)/255*Jb) formula (8)

Among them, Rout, Gout, and Bout are respectively adjusted red, green, and blue component values of image pixels; Rin, Gin, and Bin are respectively red, green, and blue component values of image pixels before adjustment; Jb is Black luminance component value; Cmax system is the maximum luminance component value; and γ system is the gamma value.

In Figure 5, the correction critical value Iref is about 105. When it is less than the correction critical value Iref, the curve 52 shows that the adjusted brightness of the maximum brightness component is positively correlated with the gamma correction value of the brightness before adjustment, and the maximum brightness component The adjusted minimum output brightness is about 50 levels; Curve 54 shows that the adjusted brightness of the non-maximum brightness component is negatively correlated with the gamma correction value of the brightness before adjustment, and the adjusted maximum output brightness of the non-maximum brightness component About 50 steps.

If the color component Cmax of the maximum brightness is greater than the correction critical value Iref, the value of the first color component after adjustment is positively correlated with the value of the first color component before adjustment, and the value of the second color component after adjustment is proportional to the value of the second color component before adjustment. Negative correlation, and the value of the third color component after adjustment is negatively correlated with the value of the third color component before adjustment, expressed by formulas (9), (10), and (11).

Rout=((255-Cmax)/255*Jb)+(Rin/255) ^1.0 *(255-(255-Cmax)/255*Jb) formula (9)

Gout=((255-Cmax)/255*Jb)+(Gin/255) ^1.0 *(255-(255-Cmax)/255*Jb) formula (10)

Bout=((255-Cmax)/255*Jb)+(Bin/255) ^1.0 *(255-(255-Cmax)/255*Jb) formula (11)

Among them, Rout, Gout, and Bout are respectively adjusted red, green, and blue component values of image pixels; Rin, Gin, and Bin are respectively red, green, and blue component values of image pixels before adjustment; Jb is black luminance component value; and Cmax is the maximum luminance component.

In Figure 5, when it is greater than the correction critical value Iref, the curve 52 shows that the adjusted brightness of the maximum brightness component is positively correlated with the brightness before adjustment; the curve 54 shows the adjusted brightness of the non-maximum brightness components and the brightness before adjustment into a negative correlation.

In step S224, the projection device 10 projects the adjusted red, green, and blue component values of each pixel, so as to maintain the consistency of the color appearance in the dark room and ambient light.

Although the embodiment provides a method for maintaining the color appearance consistency of the dark room and ambient light, those skilled in the art can also maintain the color appearance consistency of different ambient lights according to the same principle of the image correction method 200 .

The image system 1 and the image correction method 200 adjust the color gamut of the projection device 10 through the conversion of the color appearance model, and at the same time adjust the contrast and saturation of the image through image processing, so as to achieve the consistency of the color appearance in the dark room and ambient light.

FIG. 6 is a flow chart of another image correction method 600 of the image system 1 , including steps S602 to S614 for maintaining the color appearance consistency of the image. Steps S602 to S608 are used to generate color appearance representation values under ambient light. Steps S610 to S614 are used to correct the contrast and saturation of the image. Any reasonable technical changes or step adjustments fall within the scope of the disclosure of the present invention. Steps S602 to S614 are described below: Step S602: under ambient light, the color sensor 12 measures the ambient light background brightness Yb; Step S604: under ambient light, control the projection device 10 to project a test image onto the projection surface using a predetermined color gamut 16; Step S606: Under ambient light, the color sensor 12 measures a set of ambient light measurement values of black and a set of ambient light measurement values of white of the test image on the projection surface 16; Step S608: Processor 140 according to black The set of ambient light measurement values, the set of white ambient light measurement values, the ambient light adaptability area brightness, the ambient light background brightness and a set of ambient light surround parameters to generate a set of black color appearance representation values; step S610: Processor 140 performs color gamut conversion on a set of color values of pixels in the original image according to the second color gamut to generate a set of converted color values. The set of converted color values includes the first color component value, the second color component value and The third color component value; step S612: the processor 140 adds the brightness in the group of black color appearance representation values to the first color component value, the second color component value and the third color component value to generate the adjusted first color component value respectively. The color component value, the adjusted second color component value, and the adjusted third color component value; Step S614: In a dark room, the projection device 10 projects the adjusted first color component value and the adjusted second color component value and the adjusted value of the third color component.

Steps S602 to S608 are similar to steps S202 to S208 except that the test image may contain black and/or white, and only a set of color appearance representation values of black is required to be generated. Steps S610 to S614 are similar to steps S220 to S224, and the details thereof can be found in the preceding paragraphs, and will not be repeated here.

The image system 1 and the image correction method 600 adjust the contrast and saturation of the image through image processing, so as to achieve the color appearance consistency between the dark room and ambient light. The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

200: Image Correction Method

S202 to S224: Steps

Claims (16)

An image correction method of an image system, the image system includes a projection device, a color sensor and a processor, the method includes: in an ambient light environment, setting the projection device to use a first color gamut to convert a A test image is projected onto a projection surface, the test image includes black, white and at least one specific color; under the ambient light, the color sensor measures a set of ambient light measurements of the black of the test image on the projection surface value, a set of ambient light measurements for the white color, and at least one set of ambient light measurements for the at least one specific color; the processor relies on the set of ambient light measurements for the black, the set of ambient light measurements for the white color, The at least one set of ambient light measurement values for the at least one specific color, an ambient light adaptability area luminance, an ambient light background luminance, and a set of ambient light surround parameters to generate a set of color appearance representation values for the black, the white a set of color appearance representation values and at least one set of color appearance representation values of the at least one specific color; under a dark room, the projection device projects the test image onto the projection surface; under the dark room, the color sensor measuring the set of darkroom measurements for white and the set of darkroom measurements for black of the test image on the projection surface; a set of color appearance representation values, the set of darkroom measured values for the white color, a darkroom adaptive area luminance, a darkroom background luminance, and a set of darkroom surround parameters to generate at least one set of target values for the at least one specific color; the processing The processor sets the projection device to a second color gamut according to at least one set of target values of the at least one specific color, the first color gamut and the second color gamut are different; the processor sets a pixel in an original image A set of color values is subjected to color gamut conversion according to the second color gamut to generate a set of converted color values, the set of converted color values includes a first color component value, a first Two color component values and a third color component value; the processor adds one of the brightness of the black color appearance representation value to the first color component value, the second color component value and the third color component value respectively generate an adjusted first color component value, an adjusted second color component value and an adjusted third color component value; and under the dark room, the projection device projects the adjusted first color component value, the adjusted second color component value, and the adjusted third color component value. The method according to claim 1, wherein the processor setting the projection device to the second color gamut according to the at least one set of target values of the at least one specific color comprises: the processor according to the at least one specific color of the At least one set of target values adjusts at least one color temperature gain, at least one hue, and at least one saturation of the at least one specific color to set the projection device to the second color gamut. The method according to claim 1, wherein the at least one specific color includes six-axis colors. The method as described in claim 1, wherein each group of color appearance representations of the group of color appearance representation values of the black, the group of color appearance representation values of the white, and the at least one group of color appearance representation values of the at least one specific color The values include a brightness, a red-green related dimension, and a yellow-blue related dimension. The method of claim 1, wherein the second color gamut is smaller than the first color gamut. An image correction method for an image system, the image system includes a projection device, a color sensor and a processor, the method includes: Under an ambient light, setting the projection device to use a first color gamut to project a test image onto the projection surface, the test image comprising black and white; under the ambient light, the color sensor measures the projection the set of ambient light measurements for black and the set of ambient light measurements for white of the test image on the surface; the processor relies on the set of ambient light measurements for black, the set of ambient light measurements for white , an adaptive area brightness of ambient light, an ambient light background brightness and a set of ambient light surround parameters to generate a set of color appearance representation values of the black; the processor converts a set of color values of a pixel in an original image performing color gamut conversion according to a second color gamut to generate a set of converted color values, the group of converted color values including a first color component value, a second color component value and a third color component value; the processor will One of the brightness of the group of color appearance representation values of the black color is added to the first color component value, the second color component value and the third color component value to generate an adjusted first color component value, an adjusted the adjusted second color component value and an adjusted third color component value; and in a dark room, the projection device projects the adjusted first color component value, the adjusted second color component value and the adjusted The third color component value; wherein the range of the second color gamut is smaller than the first color gamut. The method as claimed in claim 1 or 6, wherein if the first color component value is greater than the second color component value, the third color component value and a correction threshold value, the adjusted first color component value and the The first color component value is positively correlated, the adjusted second color component value is negatively correlated with the second color component value, and the adjusted third color component value is negatively correlated with the third color component value. The method as described in claim 1 or 6, wherein if the value of the first color component is greater than the value of the second color component and the value of the third color component, but less than a correction threshold value, the adjusted first color component The value is positively correlated with a gamma correction value of the first color component value, the adjusted second color component value is negatively correlated with a gamma correction value of the second color component value, and the adjusted third The color component value is negatively correlated with one of the gamma correction values of the third color component value. The method of claim 1 or 6, wherein the first color gamut is greater than or equal to a DCI-P3 color gamut. The method according to claim 1 or 6, wherein the ambient light background brightness is a brightness of the set of ambient light measurement values of the black color. The method according to claim 1 or 6, further comprising: under the ambient light, the projection device stops projecting onto the projection surface, and the color sensor measures a brightness on the projection surface to generate the ambient light background brightness. The method according to claim 1 or 6, further comprising, under the ambient light, the color sensor measures a brightness of a background area to generate the ambient light background brightness. The method according to claim 1 or 6, further comprising measuring, under the ambient light, the color sensor a brightness of the white color at a stimulus point on the projection surface to generate an adaptive area brightness of the ambient light. The method as claimed in claim 1 or 6, wherein one of the set of ambient light measurements of the white color is The brightness is an absolute brightness of a reference white point, and the method further includes: under the ambient light, the projection device is turned off, the color sensor measures a brightness of the projection surface to generate a relative brightness of a reference white point; and the The processor generates the adaptive area brightness of the ambient light according to the absolute brightness of the reference white point, the background brightness of the ambient light and the relative brightness of the reference white point. The method as described in claim 14, further comprising: the processor calculating an surround ratio of the ambient light background brightness and the relative brightness of the reference white point; and the processor obtaining the set of ambient light surround parameters according to the surround ratio. The method as described in claim 1 or 6, further comprising: under the ambient light, the color sensor measures the brightness of the white on the projection surface and the brightness of a surrounding area; the processor calculates the projection A surrounding ratio of the brightness of the white on the surface and the white brightness of the surrounding area; and the processor obtains the set of ambient light surround parameters according to the surround ratio.

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