WO2006035817A1

WO2006035817A1 - Stereoscopic two-dimensional image display and stereoscopic two-dimensional image displaying method

Info

Publication number: WO2006035817A1
Application number: PCT/JP2005/017857
Authority: WO
Inventors: Isao Tomisawa; Masaru Ishikawa
Original assignee: Pioneer Corporation
Priority date: 2004-09-29
Filing date: 2005-09-28
Publication date: 2006-04-06

Abstract

The problem that display of only a stereoscopic two-dimensional image having a relief effect results in a degraded relief effect and a degraded intrigueness and hardly produces a high rendering effect is solved. A stereoscopic two-dimensional image display (100) comprises a display section (11) having an image display surface (11a) on which a two-dimensional image (17) is displayed, an image transfer panel (13) spaced from the image display surface (11a) and adapted to display a stereoscopic two-dimensional image by focusing the light emitted from the image display surface (11a) to form an image. The display (100) further comprises a transparent or semitransparent light-transmitting member (15) disposed on the opposite side to the display section (11) with respect to the image transfer panel (13) and image-forming position varying means for displaying a stereoscopic two-dimensional image as a two-dimensional image (17) by causing the image-forming position to approximately accord with the light-transmitting member (15) and to superpose the image on the light-transmitting member (15) and displaying a stereoscopic two-dimensional image by shifting the image-forming position from the light-transmitting member (15) not to superpose the image on the light-transmitting member (15).

Description

Stereoscopic two-dimensional image display apparatus and stereoscopic two-dimensional image display method

Technical field

The present invention relates to a stereoscopic two-dimensional image display device and a stereoscopic two-dimensional image display that display a stereoscopic two-dimensional image with a sense of depth by forming a two-dimensional image in space. Regarding the method.

Background art

[0002] Image display devices include various devices such as home TVs, amusement game devices, training simulators, medical surgery support systems, architectural landscape simulations, mobile phone displays, etc. Used in the field. In recent years, in image display devices used in these fields, in order to improve amusement and visibility, development of stereoscopic display technology that can provide a high sense of presence has been attempted. Stereoscopic display devices can be broadly classified into those using parallax information and those using depth information. Those using disparity information can be further divided into those using polarized glasses and those not using them.

[0003] For example, there is a lenticular lens method that uses polarized glasses in the parallax information method, where multiple screens are latent on one screen, and a semi-cylindrical lens of a certain width is connected horizontally. By viewing multiple screens through a transparent screen, it is possible to express 3D and moving images. Specifically, stripe images alternately arranged from the left and right parallax images corresponding to both eyes of the viewer are supplied to both eyes of the viewer using a lenticular lens to recognize the stereoscopic image! / (For example, refer to Patent Document 1).

[0004] However, since the lenticular lens method has a plurality of latent images on one screen, it requires computer image processing, lenticular lens design, and an accurate combination of the lens and the image, and tends to be expensive. is there. In addition, there is a method of displaying all three-dimensional coordinate information using depth information, but the amount of information becomes large.

[0005] On the other hand, by forming a two-dimensional image using a microlens array to form an image, it is possible to display a stereoscopic two-dimensional image with a simple structure and with the same force as if the three-dimensional image is projected. A two-dimensional image display device has been proposed. This stereoscopic two-dimensional image display device includes a display unit that displays a two-dimensional image including a stereoscopic image on a planar image display surface, and a microlens array camera that is disposed on the image display surface and is separated from the image display surface. In other words, an image plane of a real image (image formation) of a two-dimensional image is generated in a space located on the opposite side of the display unit. According to this three-dimensional two-dimensional image display apparatus, a sense of reality can be obtained with a very simple configuration.

[0006] Patent Document 1: Japanese Patent Laid-Open No. 10-221644

Disclosure of the invention

Problems to be solved by the invention

[0007] However, the above-described conventional stereoscopic two-dimensional image display device generates a two-dimensional image forming surface in a hollow state, so that a sense of depth is generated by the display of a real image, which is very simple. Although the structure provides a sense of realism, if you always observe the real image only at the raised position, you are actually observing only the stereoscopic two-dimensional image. There is a problem that the performance is lowered and it is difficult to maintain a high performance effect. Also, depending on the type of display image, some images are not suitable for stereoscopic two-dimensional images, such as images with a background or images that are not a black background. It caused a sense of incongruity.

Also, depending on the purpose of use of the image, it may be more convenient for the user if it is not displayed three-dimensionally. For example, when displaying a normal television broadcast or the like, an image displayed on a panel or the like, for example, may be easier to use than an image formed in the air.

[0008] As a problem to be solved by the present invention, the display of only a stereoscopic two-dimensional image that always raises a two-dimensional image reduces the unexpected effect, and maintains a high rendering effect. One example is the problem that it is difficult to perform.

In addition, as a problem to be solved by the present invention, it is possible to switch between displaying a stereoscopic two-dimensional image in the air and displaying a two-dimensional image on the real thing as necessary. One example is to provide an optimal display form.

Means for solving the problem

[0009] The stereoscopic two-dimensional image display device according to claim 1 is an image display for displaying a two-dimensional image. A stereoscopic two-dimensional display comprising: a display unit having a plane; and an image transmission panel that displays a stereoscopic two-dimensional image by imaging light emitted from the image display plane force that is spaced apart from the image display plane An image display device, wherein the three-dimensional two-dimensional image is formed by overlapping a light transmissive member disposed on a side opposite to the display unit of the image transmission panel, and the imaging and the light transmissive member. An imaging position variable means for displaying an image on the light transmissive member as a two-dimensional image, and displaying the stereoscopic two-dimensional image by making the image formation and the light transmissive member non-overlapping; It is characterized by comprising.

[0010] The stereoscopic two-dimensional image display method according to claim 10 displays a two-dimensional image on an image display surface of a display unit, and emits the image from the image display surface by an image transmission panel arranged separately on the image display surface. An image display method for displaying a stereoscopic two-dimensional image by forming an image of light to be transmitted, the light transmissive member disposed on the opposite side of the display unit of the image transmission panel, and the imaging , The stereoscopic two-dimensional image is displayed as a two-dimensional image on the light transmissive member, or the imaging and the light transmissive member are non-overlapping to display the stereoscopic two-dimensional image. A dimensional image is displayed.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of a stereoscopic two-dimensional image display apparatus and a stereoscopic two-dimensional image display method according to the present invention will be described with reference to the drawings.

1 is a perspective view of a schematic configuration of a stereoscopic two-dimensional image display device according to an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along line AA in FIG. 1, and FIG. 3 is a stereoscopic two-dimensional image shown in FIG. FIG. 6 is an operation explanatory diagram showing different image forming positions of the image display device in (a) and (b).

[0012] A stereoscopic two-dimensional image display device 100 according to the present embodiment includes a display unit 11 having an image display surface 1 la for displaying a two-dimensional image, and an image transmission panel spaced from the image display surface 1 la. (Microlens array) 13 and a transparent or translucent light-transmitting member 15 (for example, a plate-like or block-like transparent glass or transparent plastic) disposed on the opposite side of the display unit 11 of the microlens array 13 The two-dimensional image 17 shown in FIGS. 1 and 2 is obtained by making the imaging position substantially coincide with the light-transmitting member 15 and overlapping the image-forming and the light-transmitting member. On the other hand, by shifting the position of the image formation from the light transmissive member 15 and making the image formation and the light transmissive member non-overlapping, the three-dimensional shown in FIG. Imaging position varying means (not shown) for displaying the two-dimensional image 19 is provided. As a basic operation, the stereoscopic two-dimensional image display apparatus 100 forms an image of light emitted from the image display surface 11a by the microlens array 13, and displays a stereoscopic two-dimensional image 19 shown in FIG.

[0013] The display unit 11 includes a color liquid crystal display device (LCD) (not shown) having a flat image display surface 11a, a color / crite illumination unit, and a color liquid crystal drive circuit. As the display unit 11, for example, a cathode ray tube, a plasma display, or an organic electrium luminescence display may be used instead of the LCD. The color liquid crystal drive circuit outputs a display drive signal to the LCD based on the input video signal, and displays a stereoscopic two-dimensional image having a sense of depth on the image display surface 11a.

[0014] The microlens array 13 is formed, for example, by integrating two lens array halves. Each lens array half has a plurality of micro-convex lenses arranged in an array on both surfaces of a transparent substrate made of glass or resin having excellent translucency, and a lens array surface is formed on the surface. . The optical axis of each micro-convex lens formed on one surface is adjusted to be the same as the optical axis of the micro-convex lens on the other surface formed at the opposite position, and adjacent micro-convex lenses between the lens array halves. They are overlapped so that their optical axes are the same. In this specification, a force microlens array is described in which an example using a microlens array in which a lens array surface is formed on any one of the two lens array halves (a total of four surfaces) is used. However, the configuration is not limited to this.

The microlens array 13 is arranged at a position separated from the image display surface 11a of the display unit 11 by a predetermined distance (the working distance of the microphone port lens array 13). The microlens array 13 forms an image of light corresponding to an image emitted from the image display surface 11a of the display unit 11 on a stereoscopic image display surface separated by a predetermined distance on the opposite side of the image display surface 11a. As shown in FIG. 3 (a), the image displayed on the image display surface 11a is displayed on a stereoscopic image display surface which is a two-dimensional plane in space. This formed image is a force that is a two-dimensional image. If the image has a sense of depth, or if the background image on the display is black and the contrast is emphasized, it floats in space. As a result, it appears to the front observer that a 3D image of the power is projected. That is, the two-dimensional image displayed on the stereoscopic image display surface is recognized by the observer as the stereoscopic two-dimensional image 19. The three-dimensional two-dimensional image 19 is a plane on a space defined according to the working distance of the microlens array 13. In the stereoscopic two-dimensional image display device 100, an opening is provided on the front surface of the casing 21 so that an image displayed on the stereoscopic image display surface can be viewed from the front.

[0017] It is desirable that the microlens array 13 allows light corresponding to an image incident from the display unit 11 to be incident on the lens array half-body force, inverted once inside, and then emitted from the lens array half-body. Thereby, the microlens array 13 can display the two-dimensional image displayed on the display unit 11 as an upright three-dimensional two-dimensional image 19 on the three-dimensional image display surface.

[0018] The microlens array 13 is not limited to one in which two lens array halves are integrated into one set, and may be composed of one or a plurality of two or more. Good. However, when image-corresponding light is transmitted through such a single micro-convex lens, or when image-corresponding light is transmitted through three micro-convex lenses, after the incident light is inverted once inside, The image is displayed as an upright three-dimensional two-dimensional image 19 so as to be emitted.

The imaging position varying unit according to the present embodiment integrally holds the display unit 11 and the microlens array 13 while keeping the display unit 11 and the microlens array 13 fixed at a predetermined interval. By moving between the first position and the second position, overlapping and non-overlap of the imaging and the light transmitting member 15 are realized.

That is, assuming that the position of the display unit 11 and the microlens array 13 shown in FIG. 2 is the first position, when the display unit 11 and the microlens array 13 are moved to the first position, the image formation and the light-transmitting member 15 overlap, It can be recognized as a dimensional image 17.

If the positions of the display unit 11 and the microlens array 13 shown in FIG. 3 (a) are the second position, the imaging and the light transmissive member 15 do not overlap when moved to the second position. Is formed into a three-dimensional two-dimensional image 19 and displayed in a space in front of the light transmitting member 15 (opposite to the display unit 11).

Alternatively, if the position of the display unit 11 and the microlens array 13 shown in FIG. 3 (b) is the second position, the imaging and the light transmissive member 15 are non-overlapping when moved to the second position. The image is a three-dimensional two-dimensional image 19, and behind the light transmissive member 15 (display 11 side) Displayed in the space.

Here, the image formation is substantially coincident with the light transmissive member 15 that is observed as a three-dimensional two-dimensional image 19 by being positioned in the hollow position (in the medium of the light transmissive member 15). By arranging, it will be observed as a normal two-dimensional image 17 with no relief effect. In other words, the image is not raised and the image is not seen three-dimensionally by arranging the light transmissive member 15. Therefore, the stereoscopic two-dimensional image display device 100 can switch between the two-dimensional image 17 and the stereoscopic two-dimensional image 19 by changing the imaging position by the imaging position variable means. It should be noted that when the light transmitting member 15 does not transmit the light emitted from the display unit, that is, when the imaging is displayed overlapping the light transmitting member 15, the two-dimensional image 17 is not displayed on the light transmitting member 15. It is possible to make the two-dimensional image 17 more visible by attaching an object (for example, a decorative member made of metal or plastic) to the area without transmitting light. This is because it is easier to focus the eyes of the viewer because a real object, a decorative member, is present in the vicinity of the two-dimensional image 17 that is an image displayed in the light transmitting member 15. It is an effect.

FIG. 4 is an operation explanatory diagram of a modified example in which the light transmissive member can be taken in and out.

The stereoscopic two-dimensional image display device 100 is a force for changing the imaging position with respect to the light transmissive member 15 by the imaging position changing means.As a modification, the display unit 11 and the microlens array 13 are fixedly installed. The light transmissive member 15 may be held so that it can be taken in and out. In other words, the light transmissive member 15 can be moved between the third position and the fourth position so that the light transmissive member 15 can be moved forward and backward at the imaging position.

In such a modified example, as shown in FIG. 4 (a), the light transmissive member 15 is advanced to the image formation position (third position) so that the image is observed as a normal two-dimensional image 17. Then, as shown in FIG. 4 (b), by removing the light transmissive member 15 from the imaging position (moving it to the fourth position), the imaging is displayed in a hollow shape, and the stereoscopic two-dimensional image is displayed. Observed as 19. That is, the display of the two-dimensional image 17 or the stereoscopic two-dimensional image 19 can be switched without moving the display unit 11 or the microlens array 13.

FIG. 5 is an operation explanatory diagram showing the switching process from the two-dimensional image to the stereoscopic two-dimensional image in (a) to (c). The display method of the stereoscopic two-dimensional image display device 100 is to switch the mode between the two-dimensional image 17 and the stereoscopic two-dimensional image 19 completely, for example, 3D game play and normal TV broadcast viewing.

There are two cases: a case where the two-dimensional image 17 is displayed in a different state and a case where the two-dimensional image 17 is smoothly switched to the three-dimensional two-dimensional image 19. In the latter case, it is preferable to link the video at the time of switching for the purpose of effectively switching the 2D image 17 to the stereoscopic 2D image 19 to enhance the production effect!

[0023] As an example of an image linked to the switching from the two-dimensional image 17 to the three-dimensional two-dimensional image 19, for example, as shown in FIG. The background image 41 of the two-dimensional image 17 is faded out from the state displayed overlapping the transparent member 15 as shown in FIG. 5B. At the same time, the display portion 11 and the microlens array 13 are gradually moved by the imaging position varying means, and the imaging and the light-transmitting member 15 are made non-overlapping, so that the two-dimensional image 17 is raised and the two-dimensional image is displayed. Switch to dimensional image 19. At this time, as shown in FIG. 5 (c), a high rendering effect can be obtained by causing the stereoscopic two-dimensional image 19 to move along with the enlargement while operating (such as making a smudge out of motion).

FIG. 6 is a structural cross-sectional view of a modified example in which a light transmissive flat display device is used as the light transmissive member, and FIG. 7 is a state in which the background is displayed on the flat display device of the modified example shown in FIG. FIG. 8 is an operation explanatory diagram showing a state in which a screen frame is displayed on the flat display device of the modification shown in FIG.

As shown in FIG. 6, in the stereoscopic two-dimensional image display device 100, the light transmissive member 15 may be a light transmissive flat display device 31. As the flat display device 31, for example, a liquid crystal display device, a transparent organic EL display device, or the like can be used.

When the positions of the display unit 11 and the microlens array 13 are the positions shown in FIG. 6 (a) (first position), the image formation and the flat display device 31 overlap, and this image formation is a two-dimensional image 17. It becomes. Further, when the positions of the display unit 11 and the microlens array 13 are the positions shown in FIG. 6B (second position), the imaging and the flat display device 31 are non-overlapping, and this imaging is two-dimensional. A dimensional image 19 is displayed in front of the flat display device 31 (on the side opposite to the display unit 11). In such a modified example, as shown in FIG. The background image 33 and the like related to the stereoscopic two-dimensional image 19 can be displayed on the flat display device 31 (light transmissive member) on the display unit 11 side.

Further, since the light transmissive member is the flat display device 31, as shown in FIG. 8, the image formation and the flat display device 31 overlap each other, and in the state of the two-dimensional image 17, a screen frame 35 like a frame. Can be displayed. Thereby, the state of the two-dimensional image 17 can be displayed more naturally.

[0026] Note that the stereoscopic two-dimensional image display device 100 can be provided with the screen frame 35 even when the flat display device 31 is not used. That is, in this case, an actual screen frame (not shown) corresponding to the screen frame 35 is added to the periphery of the light transmissive member 15 as a light non-transmissive member. In this way, by attaching a frame like a frame to the periphery of the light transmissive member, that is, the existence of a light non-transmissive member that is an entity in the vicinity of the two-dimensional image 17, The state can be displayed more naturally.

[0027] Further, the light transmissive member 15 may be electrically switchable between light transmission and diffusion, for example. In such a case, in the state of the two-dimensional image 17 in which the imaging and the flat display device 31 overlap, diffusion (white turbidity) occurs, and in the state of the stereoscopic two-dimensional image 19 in which the imaging and the light transmitting member 15 do not overlap. Make it transparent. In the diffused (white turbid) state, there is an effect of diffusing light and widening the viewing angle, so that the displayed image can be viewed with a wider oblique positional force. Furthermore, transmission and diffusion may be switched gradually by linking with the image or imaging position variable means (gradient change of white turbidity, transmittance, etc.). In this case, it is possible to obtain a display effect that gradually raises the stereoscopic two-dimensional image 19 from the two-dimensional image 17. Therefore, it is possible to display the state of the two-dimensional image 17 more naturally and more effectively to switch to the state of the stereoscopic two-dimensional image 19.

[0028] Further, the imaging position varying means may be a variable focus lens provided in the image transmission panel. A so-called liquid crystal lens can be suitably used as the variable focus lens. The focus variable lens can continuously change the direction of the major axis of the liquid crystal molecules in the vertical direction by controlling the magnitude of the applied voltage. Therefore, the refractive index changes continuously with respect to the light incident on the orientation direction of the liquid crystal molecules. By changing the focal length using such a variable focus lens, the position of image formation can be changed to a light transmissive member or the light transmissive member. It is displayed at a position shifted from the member, and the display of the two-dimensional image 17 or the three-dimensional two-dimensional image 19 can be switched without moving the display unit 11, the image transmission panel, and the light-transmissive member 15. . As a result, a switching mechanism between the two-dimensional image and the stereoscopic two-dimensional image can be simply configured.

Therefore, according to the stereoscopic two-dimensional image display device 100 according to the present embodiment, the transparent or translucent light transmissive member 15 disposed on the opposite side of the display unit 11 of the microphone aperture lens array 13; The three-dimensional image 19 is displayed as the two-dimensional image 17 by making the position of image formation substantially coincide with the light transmissive member 15 and overlapping the image formation and the light transmissive member. The image forming position variable means for displaying the stereoscopic two-dimensional image 19 by shifting the position of the light transmitting member 15 from the light transmitting member 15 and making the image forming and the light transmitting member non-overlapping is provided. The two-dimensional image 17 and the three-dimensional two-dimensional image 19 can be displayed in a switchable manner. For example, the normal two-dimensional image 17 displayed on the light-transmitting member 15 can be displayed as a three-dimensional two-dimensional image 19. By projecting from the member 15, the projecting effect of the image A more enhanced sexual can further improve the performance effect. It can also be used as an ordinary display device for two-dimensional images, so it is easy to observe images with backgrounds or images that are not suitable for a stereoscopic two-dimensional image 19, for example, with a black background. it can.

[0030] In the stereoscopic two-dimensional image display method, for example, a normal two-dimensional image 17 displayed on the light transmissive member 15 is transmitted as a stereoscopic two-dimensional image 19 by switching the display mode. It is raised from the sex member 15, and the effect of raising the image is improved. In addition, a normal two-dimensional image 17 can be displayed.

Therefore, according to the stereoscopic two-dimensional image display method according to the present embodiment, the transparent or translucent light transmissive member 15 disposed on the opposite side of the display unit 11 of the microlens array 13 is connected to the transparent lens 15. The three-dimensional image is displayed as the two-dimensional image 17 by making the positions of the images substantially coincide with each other to overlap the image formation and the light transmissive member, or the position of the image formation is the light transmissive member 15. The three-dimensional two-dimensional image 19 is displayed by making the image formation and the light transmissive member non-overlapping from each other, so that the normal two-dimensional image 17 displayed on the light transmissive member 15 is displayed. By switching the display mode, the two-dimensional two-dimensional image 19 is raised from the light-transmitting member 15, and the effect of projecting is further improved by enhancing the image's protrusion effect. Can be further improved. Further, since the normal two-dimensional image 17 can be displayed, it is suitable for the stereoscopic two-dimensional image 19 and can be easily observed, for example, an image with a background or a black background.

This application is based on a Japanese patent application filed on September 29, 2004 (Japanese Patent Application No. 2004-285208), the contents of which are incorporated herein by reference.

Brief Description of Drawings

FIG. 1 is a perspective view of a schematic configuration of a stereoscopic two-dimensional image display device according to an embodiment of the present invention.

2 is a cross-sectional view taken along line AA in FIG.

3 is an operation explanatory diagram showing different imaging positions of the stereoscopic two-dimensional image display device shown in FIG. 2 in (a) and (b).

FIG. 5 is an operation explanatory diagram showing the switching process from a two-dimensional image to a stereoscopic two-dimensional image in (a) to (c).

FIG. 6 is a configuration diagram of a modified example in which a light transmissive flat display device is used as the light transmissive member.

FIG. 7 is an operation explanatory view showing a state in which a background is displayed on the flat display device of the modification shown in FIG.

8 is an operation explanatory diagram showing a state in which a screen frame is displayed on the flat display device of the modified example shown in FIG.

Explanation of symbols

[0033] 11 Display

11a Image display surface

13 Micro lens array (image transmission panel)

15 Light transmissive member

17 Two-dimensional image

19 3D image

31 Light transmissive flat panel display Screen frame

Stereoscopic two-dimensional image display device

Claims

The scope of the claims

[1] a display unit having an image display surface for displaying a two-dimensional image;

A stereoscopic two-dimensional image display device comprising: an image transmission panel that displays a stereoscopic two-dimensional image by imaging light emitted from the image display surface that is spaced apart from the image display surface;

A light transmissive member disposed on the opposite side of the display unit of the image transmission panel, and the imaging and the light transmissive member are overlapped to form the stereoscopic two-dimensional image on the light transmissive member. An imaging position variable means for changing the display and displaying the stereoscopic two-dimensional image in space by making the imaging and the light transmissive member non-overlapping;

A stereoscopic two-dimensional image display device comprising:

[2] The imaging position varying means moves at least one of the display unit and the image transmission panel between a first position and a second position, respectively, to form the imaging and the light transmissive member. The three-dimensional two-dimensional image display device according to claim 1, wherein overlapping and non-overlapping are realized.

[3] The imaging position varying means moves the light transmissive member between a third position and a fourth position to realize overlap and non-overlap between the image formation and the light transmissive member. The three-dimensional two-dimensional image display device according to claim 1, characterized in that:

4. The stereoscopic two-dimensional image display device according to claim 1, wherein the light transmissive member is capable of switching between transmission and diffusion of light emitted from the image display surface. .

5. The three-dimensional image according to claim 4, wherein when the imaging and the light transmissive member overlap, the light transmissive member diffuses light emitted from the image display surface. Two-dimensional image display device.

6. The stereoscopic two-dimensional image display device according to claim 1, wherein the light transmissive member is a light transmissive flat display device.

[7] The portion of the light transmissive member that does not transmit light emitted from the display unit is provided with a collar member that does not transmit light! 6-dimensional Two-dimensional image display device.

8. The stereoscopic two-dimensional image display device according to any one of claims 1 to 7, wherein the imaging position changing means is a variable focus lens provided in the image transmission panel.

9. The stereoscopic two-dimensional image display device according to claim 1, wherein the image transmission panel is a microlens array.

[10] Display a two-dimensional image on the image display surface of the display unit,

An image display method for displaying a stereoscopic two-dimensional image by forming an image of light emitted from the image display surface by an image transmission panel spaced apart on the image display surface, the display unit of the image transmission panel The three-dimensional two-dimensional image is displayed as a two-dimensional image on the light transmissive member by overlapping the light transmissive member disposed on the opposite side of the image and the imaging, or the connection A stereoscopic two-dimensional image display method, wherein the stereoscopic two-dimensional image is displayed by making an image and the light transmissive member non-overlapping.