JP7609159B2 - Head-up display - Google Patents

Description

This disclosure relates to correcting distortion of a virtual image displayed by a head-up display installed in a vehicle.

A conventional head-up display is disclosed in Patent Document 1. This head-up display reflects display light emitted from a display that displays an image off a reflector or the windshield of the vehicle, and displays a virtual image of the display light through the windshield. In such a head-up display, distortion occurs in the virtual image during the process of reflection off the reflector or windshield.

Therefore, the head-up display disclosed in Patent Document 1 has a distortion correction processing function that uses image deformation, known as warping, to correct the distortion of the virtual image described above.

JP 2011-105306 A

However, the inventors of the present disclosure recognized that because the warping setting value is determined based on the center point within the eyebox, there is an issue in that the display quality of the head-up display deteriorates the further the line of sight deviates from the center point within the eyebox.

In view of the above-mentioned problems, the present disclosure aims to provide a head-up display with high display quality.

The head-up display of the present disclosure includes:
A head-up display including a display unit that outputs a display light representing an image and a control unit that controls the display unit, the display light being reflected by a windshield of a vehicle to allow a virtual image of the display light to be viewed from an eye box,
One warping setting value is set for one of the eye boxes,
The control unit deforms the image based on the warping setting value to correct distortion of the virtual image,
The warping settings are set as follows:
(a) the warping setting value is optimized for the center point of the eyebox , and the statistical variation of the evaluation value of the virtual image viewed from a plurality of points within the eyebox is less than a predetermined value; or
(b) if (a) is not achieved, then the warping settings are not optimized for the eyebox center point and the statistical variation is less than a predetermined value.

The present disclosure makes it possible to provide a head-up display with high display quality.

Schematic diagram of the configuration of a head-up display according to the present disclosure. A diagram showing an image before correction and a warping mesh. A diagram showing virtual images corresponding to different viewpoints within the eyebox. A diagram showing the procedure for calculating the warping mesh

The head-up display of the present disclosure will be described with reference to the attached drawings 1-4. In each drawing, the left-right direction of the vehicle is illustrated as the X direction, the up-down direction of the vehicle as the Y direction, and the front-rear direction of the vehicle as the Z direction. Also, in FIG. 1, the chief ray of the display light PL is illustrated for easy visual understanding.

The head-up display HUD is an in-vehicle instrument that projects a display light PL representing vehicle information (driving speed, various vehicle warnings, route guidance information, etc.) onto the windshield WS of the vehicle and displays the vehicle information as a virtual image of the display light PL. A vehicle occupant P can view the virtual image by viewing the windshield WS from within the eye box, which is the area where the virtual image can be viewed.

The head-up display HUD has a display unit 1 that outputs display light PL, a reflecting unit 2 that reflects the display light PL toward the windshield WS, a case 3 and a control circuit board.

The display unit 1 is an image display device such as a liquid crystal display, an organic electroluminescence display, or a rear projection projector. The display unit 1 is controlled by a control circuit board to display an image representing vehicle information, and outputs display light PL from this image.

The reflecting unit 2 is a concave mirror that can rotate around a rotation axis AX extending in the left-right direction of the vehicle (X direction in Figure 1).

The reflector 2 is configured to be rotatable from a first angle to an nth angle (n is a natural number equal to or greater than 2). When the reflector 2 is at the first angle, the virtual image visible area is located in the eye box EB1 at the first position, and the virtual image V1 is visible from the eye box EB1. When the reflector 2 is at the nth angle, the virtual image visible area is located in the eye box EBn at the nth position, and the virtual image Vn is visible from the eye box EBn. In other words, by rotating the reflector 2, the virtual image visible area can be moved in the vertical direction of the vehicle (Y direction in FIG. 2) within the range from the eye box EB1 to the eye box EBn, and the virtual image visible area can be adjusted to match the height of the passenger's viewpoint.

When an instruction to adjust the virtual image visible area is input to the control circuit board by an operating means such as a switch provided on the vehicle's steering wheel, the reflecting part 2 rotates under the control of the control circuit board, and the virtual image visible area is adjusted.

Case 3 is a case that houses display unit 1, reflector unit 2, and control circuit board. Case 3 has an emission opening that emits display light PL toward windshield WS. The emission opening of case 3 is covered by a translucent dust cover 31 such as an acrylic resin plate.

The control circuit board is a circuit board having an arithmetic integrated circuit (arithmetic unit) that controls the display unit 1 and the reflective unit 2, and a non-volatile memory (storage unit) such as a flash memory.

(Distortion correction process based on warping settings)
The control circuit board performs a warping process to geometrically deform the image to be displayed on the display unit 1 in order to correct distortion of the virtual image caused by the curved shape of the windshield WS. This warping process deforms each point OP of a mesh area obtained by dividing the pre-correction image OM into a lattice shape to match each point WP of a warping mesh (warping setting value) WM. This warping mesh WM is stored in a non-volatile memory of the control circuit board. To give a specific example, each point OP (0,0)...OP (4,4) of the mesh area obtained by dividing the pre-correction image OM into 16 lattice shapes is made to correspond to each point WP (0,0)...WP (4,4) of the warping mesh WM, and the image of each divided area of the pre-correction image OM is texture-mapped to each area of the warping mesh WM.

The warping mesh WM of the control circuit board is set with one warping mesh for each angle from the first angle to the nth angle of the reflector 2. In other words, one warping mesh WMx is uniquely set for an eye box EBx where the reflector 2 is at the xth angle and the virtual image visible area is at the xth position.

Here, the inventors of the present disclosure recognized that when the reflecting unit 2 is at an angle x and the image displayed on the display unit 1 is deformed by a warping mesh WMx corresponding to the eye box EBx, the degree of distortion of the virtual image perceived varies depending on the position of the viewer's viewpoint within the eye box.

Specifically, the inventors of the present disclosure recognized that the degree of distortion of a virtual image Vx(1,1) viewed from the central point EBx(1,1) of the eye box EBx differs from the degree of distortion of a virtual image Vx(0,0)...Vx(2,2) viewed from the four corner points EBx(0,0)...EBx(2,2) of a rectangle centered on the central point EBx(1,1).

The inventors of the present disclosure have recognized that when one warping mesh WMx is uniquely set for an eye box EBx in which the reflecting portion 2 is at an angle x and the virtual image visible area is at a position x, if there is a large variation in the degree of distortion of the virtual image viewed depending on the position of the viewer's viewpoint within the eye box EBx, there is a problem in that the display quality of the virtual image displayed by the head-up display HUD decreases, thereby reducing the commercial value.

To solve this problem, a warping mesh WMx is calculated that has a small variation in the degree of distortion of the virtual image perceived depending on the position of the viewer's viewpoint within the eye box EBx, using the procedure described below.

(Warping setting value calculation procedure)
The calculation procedure for the warping mesh WMx that is uniquely determined for the eye box EBx in which the reflecting portion 2 is at the xth angle and the virtual image visible region is at the xth position will be described below.

(First step S1: Setting the initial value of the warping mesh WMx)
The warping mesh WMx that minimizes the distortion of the virtual image Vx (1, 1) when viewed from the center point (1, 1) of the eye box EBx is set as an initial value. After setting, the process proceeds to the second step S2.

(Second step S2: capturing a virtual image)
A virtual image is captured when viewed from each point of the eye box EBx. Specifically, virtual images Vx(0,0)...Vx(2,2) are captured when viewed from five points, namely, the central point EBx(1,1) of the eye box EBx and the four corner points EBx(0,0)...EBx(2,2) of a rectangle centered on this point. After capturing the images, the process proceeds to the third step S3.

(Third step S3: Evaluation of virtual image)
An evaluation value for evaluating the display quality of each virtual image Vx(0,0)...Vx(2,2) is calculated. This evaluation value is calculated based on the amount of rotation, the amount of enlargement/reduction, and the amount of translation of each virtual image Vx(0,0)...Vx(2,2) with respect to the image OM before deformation. After the calculation, proceed to the fourth step S4.

(Fourth step S4: Calculating statistical variation of evaluation)
The statistical variation of the evaluation values calculated in the third step S3 is calculated. This statistical variation is, for example, a coefficient of variation (relative standard deviation) obtained by dividing the standard deviation by the arithmetic mean. The statistical variation may be a variance or a standard deviation, but from the viewpoint of treating different types of head-up displays with the same evaluation criteria, it is preferable to use a coefficient of variation expressed as a percentage. After the calculation, the process proceeds to the fifth step S5.

(Fifth step S5: Evaluation of calculated warping mesh)
The warping mesh WMx is evaluated based on the coefficient of variation calculated in the fourth step S4, and if the evaluation is below a predetermined level, it is determined that the warping mesh WMx needs to be adjusted. Specifically, if the coefficient of variation is 0.1 or more, it is determined that the warping mesh WMx needs to be adjusted, and the process proceeds to the sixth step S6. If the coefficient of variation is less than 0.1, it is determined that the warping mesh WMx has low distortion variation in the virtual image and high display quality regardless of the position of the viewpoint in the eye box EBx, and the process proceeds to the seventh step S7.

(Sixth step S6: Adjustment of warping mesh)
The warping mesh WMx is recalculated so that the distortion of the virtual image Vx(1,1) is minimized when viewed from a point EBx(a,b) in the eye box EBx. Specifically, the warping mesh WMx is recalculated by setting a point EBx(a,b) that is moved a predetermined distance toward the point in the eye box EBx with the worst evaluation value calculated in the third step S3. Alternatively, the point EBx(a,b) may be calculated from the evaluation value calculated in the third step S3 and the statistical variation of the evaluation calculated in the fourth step S4. After the warping mesh WMx is recalculated, the process proceeds to the second step S2.

(Seventh step S7: Determination of warping mesh)
The warping mesh WMx having a coefficient of variation of less than 0.1 in the fifth step S5 is adopted as the warping mesh of the eye box EBx in which the reflector 2 is at the xth angle and the virtual image visible region is at the xth position. The adopted warping mesh WMx is stored in the non-volatile memory of the control circuit board as the warping mesh corresponding to the xth angle of the reflector 2.

The above-mentioned steps from the first step S1 to the seventh step S7 are performed for each of the eye boxes EB1 to EBn.

By configuring it in this manner, it is possible to provide a head-up display with high display quality, with little variation in the degree of distortion of the virtual image perceived depending on the position of the viewer's viewpoint within the eyebox.

The head-up display HUD of the present disclosure may be modified as follows:

The warping mesh WMx may be calculated by an evolutionary algorithm such as a genetic algorithm. Alternatively, the warping mesh WMx may be calculated by multiple regression analysis using parameters such as the curvature of the reflector 2 at the position where the display light PL is incident, which changes depending on the angle of the reflector 2, and the curvature of the windshield.

HUD: Head-up display 1: Display section 2: Reflection section OM: Image before deformation WM: Warping mesh (warping setting value)
PL: Main ray of display light WS: Windshield EB1-EBn: Eye box V1-Vn: Virtual image

Claims (4)

A head-up display including a display unit that outputs a display light representing an image and a control unit that controls the display unit, the display light being reflected by a windshield of a vehicle to allow a virtual image of the display light to be viewed from an eye box,
One warping setting value is set for one of the eye boxes,
The control unit deforms the image based on the warping setting value to correct distortion of the virtual image,
The warping settings are set as follows:
(a) the warping setting value is optimized for the center point of the eyebox , and the statistical variation of the evaluation value of the virtual image viewed from a plurality of points within the eyebox is less than a predetermined value; or
(b) if (a) is not achieved, the warping settings are not optimized for the center of the eyebox and the statistical variation is less than a predetermined value;
A head-up display that features The evaluation value is calculated based on a rotation amount, a scaling amount, and a translation amount of the virtual image with respect to the image before the deformation.
2. The head-up display according to claim 1 . a rotatable reflecting portion that reflects the display light onto the windshield;
The eye boxes are set in accordance with the rotational positions of the reflecting parts,
2. The head-up display according to claim 1 . The statistical variation being less than a predetermined value means that the coefficient of variation of the statistical variation is 0.1 means less than
2. The head-up display according to claim 1 .

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