4.2 Stereoscopic Display

This chapter explains restrictions for comfortable viewing of stereoscopic images by users. When testing the guideline items in this chapter and when checking how images appear stereoscopically, increase the 3D depth slider to its maximum value. The 3D depth slider is used to adjust the stereoscopic display for individual differences, but stereoscopic images must be shown correctly even when the 3D depth slider is at its maximum value.

The following symptoms are related to sections 4.2.2 Inappropriate Stereoscopic Display and 4.2.3 Parallax Restrictions and are not included in the guidelines for technical reasons; however, if these symptoms keep occurring continuously and impede game progress, they are considered as general bugs.

  • Adjusting the 3D depth slider to maximum always results in a complete inability to display stereoscopic images properly due to an overly large parallax.
  • Significant contradiction of foreground/background relationships keeps occurring, hindering proper stereoscopic display.

4.2.1 Considerations for the Development of Children's Eyes

There is some concern that viewing 3D images for extended periods of time might negatively affect eye development in children ages six and younger. The Nintendo 3DS system’s Parental Controls feature can disable the display of 3D images, regardless of the position of the 3D depth slider. Nintendo plans to issue announcements that the stereoscopic display feature should be disabled when children ages six and younger play games on Nintendo 3DS systems. Therefore, when developing applications aimed at younger users, keep in mind that some children may not be able to enjoy 3D content.

No required guideline items.

4.2.2 Inappropriate Stereoscopic Display

Using the Nintendo 3DS system’s stereoscopic display, it is possible to intentionally display the following types of images. Regardless of whether these images and video can be correctly shown stereoscopically, it is very likely that they will cause the user to feel uncomfortable.

To avoid displaying inappropriate stereoscopic images on Nintendo 3DS systems, applications are prohibited from displaying any images or video which correspond to the prohibited cases described below. Additionally, Nintendo recommends (but does not require) correcting images/video in cases where correction of a constantly-contradictory foreground/background relationship between objects would be technically difficult, such as in scenes where 3D photos and polygons overlap.

  • Images that are processed differently for the left and right eyes for some purpose other than stereoscopic depth
    Examples include adding different patterns, using images of different sizes or ones that are shifted vertically relative to each other, and applying different effects to the images for the left and right eyes. This includes using completely unrelated images as the left and right images.
  • Images with inverted stereoscopic depth (swapping the left and right images)
    An image's depth appears to be inverted when the images for the left and right eyes are reversed. In other words, this occurs when the image for the left eye is shown to the right eye and vice versa.
  • Images that are not synchronized between the left and right eyes
    Images that fall under this category include those where the timelines of the right-eye and left-eye images are out of sync, or that don't update for each eye simultaneously; for example, updating for the right eye on odd frames and for the left eye on even frames. If the left and right images are not synchronized, this has the unfortunate consequence of displaying completely different images to the user's left and right eye during scene transitions. Likewise, whenever an on-screen object moves up or down, its position gets vertically out of sync between the left and right images.

The following case is not prohibited (owing to the technical difficulty of complying at all times), but should be avoided as much as possible. If the following case occurs constantly in your application, or occurs less often but makes it significantly harder to visually recognize or understand the image, it may be considered a general bug.

  • Objects that have contradictory foreground/background relationships
    When two overlapping objects are shown stereoscopically, the object in front is usually visible and the object behind it is hidden. 3D images that contradict this foreground/background relationship—in which an object is concealed by some object behind it, for example—can cause user discomfort.

However, when you take images captured by the outer cameras or 3D content saved in the shared region and use it without modification, the prohibition above may apply to the camera images or 3D content. If this is the case, your application does not need to restrict how the captured images and other content are displayed. For example, the user may intentionally capture different images with the left and right outer cameras. In cases such as this it is acceptable for the application to stereoscopically display these images without modification or save the images as a 3D photo.

Note:

When capturing images with the outer cameras, it is necessary to set the various parameters of the two outer cameras to identical values to avoid inappropriate stereoscopic display. See the Programming Precautions for details.

 

Avoid using a shared region to save any 3D content that could be subject to the prohibition described above, and—as much as possible—avoid implementing features that allow users to create such 3D content. As referred to herein, 3D content refers to all content that can be stereoscopically displayed.

Contact Nintendo at support@noa.com if you would like to display any images, video, or other content that falls under the prohibited items described above.

4.2.2.1 Prohibition of Inappropriate Stereoscopic Display

Guideline Item

Applications must not display inappropriate stereoscopic images.

Software to Be Tested

Applications that support stereoscopic display.

Exceptions

If the following cases apply:

  • On either the right or left-eye image, there is an object that does not appear on the other image; however, the object is reasonably considered to be out of the field of view of one camera.
  • There is difference between the images due to the difference of the angles from which the object is viewed.
  • Images appear different due to physically possible reflection.
  • Images are vertically shifted due to physically possible reflection on curved surfaces or refraction.
  • Patterns or objects scaled down without applying anti-aliasing appear differently on the left and right-eye images when viewed on a per-pixel level.
  • Images captured by the outer cameras or 3D content obtained from the shared region that failed any of the Pass/Fail Determination criteria are displayed without modification.
Test Method

In scenes where the 3D LED is illuminated, play the application with the 3D depth slider at its maximum value.

Pass/Fail Determination

Passes if all of the following conditions are met.

  • There is no difference between the left-eye and right-eye images in characteristics such as the colors, shapes, size and pattern of an object.
  • There is no vertical shift between the left-eye and right-eye images.
  • The same effects are used on the left-eye and right-eye images.
  • Two completely different images are not displayed for the left-eye and right-eye images.
  • The depth of the stereoscopic image is not inverted.
  • The left-eye and right-eye images are updated simultaneously.
  • There is no temporal difference between the left-eye and right-eye images.

4.2.3 Parallax Restrictions

The Nintendo 3DS system adds parallax to left and right images on the upper screen to represent depth both into and out of the screen. However, excessive parallax can cause user discomfort. We therefore recommend that you keep the parallax between the left and right images within the following ranges:

Table 4-1 Recommended Parallax Range
Depth Direction Parallax

Into Screen (Away from User)

10.0 mm (52 pixels) or less

Out of Screen (Toward User)

5.0 mm (26 pixels) or less

The value indicated with "mm" in this section is based on the value used for CTR systems. A “pixel” has dimensions of 0.192 mm × 0.192 mm and combines one pixel for the left eye with one for the right. Although it is acceptable to use only CTR systems when testing and adjusting the parallax values for your application, be aware that the physical parallax when playing on SPR, SNAKE, or CLOSER systems is greater than that of CTR systems, even though the number of pixels is the same. If the user is viewing the screen from the distance recommended in the various manuals, then the level of burden on their eyes should be roughly the same no matter which type of system they use. Nonetheless there have been cases where users have felt different levels of stereoscopic effect from CTR systems versus SPR, SNAKE, and CLOSER systems. Therefore, when you test and adjust the amount of parallax in the content you create—particularly pre-rendered content such as video, where the user cannot adjust the parallax themselves with the 3D depth slider—Nintendo recommends using not just CTR systems, but also SPR or CLOSER systems with their larger screens.

The specific examples below are acceptable even if you apply parallax that exceeds the recommended range:

  • Displaying 3D photos or video that are taken or recorded by the user or acquired from elsewhere
    It is acceptable for the parallax to exceed the recommended range in applications that allow users to display 3D photos or video that either has been taken or recorded by the user with the outer cameras or is saved in the shared region, because these applications cannot restrict the parallax of 3D photos and video.
  • Exceeding the recommended parallax range for 1 second or less
    If the parallax exceeds the recommended range for 1 second or less, the human eye cannot adjust quickly enough to catch up to it. As long as the human eye does not adjust to the parallax, it is difficult to notice when the recommended range is exceeded, and therefore does not pose a problem.

No required guideline items.

4.2.4 Displaying a Message That Prompts the User to Take a Break

Users viewing stereoscopic images for long periods of time can experience accumulated fatigue even in the absence of obvious symptoms. Taking a 10- to 15-minute break every half hour can significantly alleviate this fatigue.

For this reason, to help users more comfortably play games with stereoscopic imagery for extended time periods, we recommend that applications display a message that prompts the user to take a break after approximately one half-hour of gameplay. This message can be provided whenever it is convenient for the application. See section 4.5.1 Health and Safety Warnings on Screen for more information on the content of the message to display.

No required guideline items.

 


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