Use Raw Depth in your Android NDK app

The Raw Depth API provides depth data for a camera image that has higher accuracy than full Depth API data, but does not always cover every pixel. Raw depth images, along with their matching confidence images, can also be further processed, allowing apps to use only the depth data that has sufficient accuracy for their individual use case.

Device compatibility

Raw Depth is available on all devices that support the Depth API. The Raw Depth API, like the full Depth API, does not require a supported hardware depth sensor, such as a time-of-flight (ToF) sensor. However, both the Raw Depth API and the full Depth API make use of any supported hardware sensors that a device may have.

Raw Depth API vs full Depth API

The Raw Depth API provides depth estimates with higher accuracy, but raw depth images may not include depth estimates for all pixels in the camera image. In contrast, the full Depth API provides estimated depth for every pixel, but per-pixel depth data may be less accurate due to smoothing and interpolation of depth estimates. The format and size of depth images are the same across both APIs. Only the content differs.

The following table illustrates the differences between the Raw Depth API and the full Depth API using an image of a chair and a table in a kitchen.

API Returns Camera image Depth image Confidence image
Raw Depth API
  • A raw depth image that contains a very accurate depth estimate for some, but not all, pixels in the camera image.
  • A confidence image that gives the confidence for every raw depth image pixel. Camera image pixels that do not have a depth estimate have a confidence of zero.
Full Depth API
  • A single "smoothed" depth image that contains a depth estimate for every pixel.
  • No confidence image is provided with this API.
 N/A

Confidence images

In confidence images returned by the Raw Depth API, lighter pixels have higher confidence values, with white pixels representing full confidence and black pixels representing no confidence. In general, regions in the camera image that have more texture, such as a tree, will have higher raw depth confidence than regions that don’t, such as a blank wall. Surfaces with no texture usually yield a confidence of zero.

If the target device has a supported hardware depth sensor, confidence in areas of the image close enough to the camera will likely be higher, even on textureless surfaces.

Compute cost

The compute cost of the Raw Depth API is about half of the compute cost for the full Depth API.

Use cases

With the Raw Depth API, you can obtain depth images that provide a more detailed representation of the geometry of the objects in the scene. Raw depth data can be useful when creating AR experiences where increased depth accuracy and detail are needed for geometry-understanding tasks. Some use cases include:

  • 3D reconstruction
  • Measurement
  • Shape detection

Prerequisites

Make sure that you understand fundamental AR concepts and how to configure an ARCore session before proceeding.

Enable Depth

In a new ARCore session, check whether a user's device supports Depth. Not all ARCore-compatible devices support the Depth API due to processing power constraints. To save resources, depth is disabled by default on ARCore. Enable depth mode to have your app use the Depth API.

int32_t is_depth_supported = 0;

// Check whether the user's device supports the Depth API.
ArSession_isDepthModeSupported(ar_session, AR_DEPTH_MODE_AUTOMATIC,
                               &is_depth_supported);
ArConfig* ar_config = NULL;
ArConfig_create(ar_session, &ar_config);
if (is_depth_supported) {
  ArConfig_setDepthMode(ar_session, ar_config, AR_DEPTH_MODE_AUTOMATIC);
}
CHECK(ArSession_configure(ar_session, ar_config) == AR_SUCCESS);
ArConfig_destroy(ar_config);

Acquire the latest raw depth image

Call ArFrame_acquireRawDepthImage16Bits() to acquire the latest raw depth image.

int64_t previous_depth_image_timestamp_ns = -1;
int64_t depth_image_timestamp_ns;
ArImage* depth_image = NULL;

// Acquire the raw depth image for the current frame.
ArStatus acquire_image_status =
    ArFrame_acquireRawDepthImage16Bits(ar_session, ar_frame, &depth_image);

if (acquire_image_status == AR_SUCCESS) {
  // Optional: compare raw depth image timestamps. Use this check if your app
  // uses only new depth data.
  ArImage_getTimestamp(ar_session, depth_image, &depth_image_timestamp_ns);
  if (depth_image_timestamp_ns != previous_depth_image_timestamp_ns) {
    // Raw depth image is based on new depth data.
    previous_depth_image_timestamp_ns = depth_image_timestamp_ns;
    // …
  }
  // Release the acquired image.
  ArImage_release(depth_image);
}

Not all image pixels returned via the Raw Depth API will contain depth data, and not every ARCore frame will contain a new raw depth image. To determine whether the raw depth image for the current frame is new, compare its timestamp with the timestamp of the previous raw depth image. If the timestamps are different, the raw depth image is based on new depth data. Otherwise, the depth image is a reprojection of previous depth data.

Acquire the latest confidence image

Call ArFrame_acquireRawDepthConfidenceImage() to acquire the confidence image. You can use the confidence image to check the accuracy of each raw depth pixel. Confidence images are returned in Y8 format. Each pixel is an 8-bit unsigned integer. 0 indicates the least confidence, while 255 indicates the most.

// Acquire the raw depth confidence image.
ArImage* confidence_image = NULL;
ArStatus acquire_image_status = ArFrame_acquireRawDepthConfidenceImage(
    ar_session, ar_frame, &confidence_image);

if (acquire_image_status == AR_SUCCESS) {
  // …
  // Release the acquired image.
  ArImage_release(confidence_image);
}