The image structure describes the format of the image and contains a pointer to the start of image data. Images are always stored in row-major order: the data pointer points to the upper left pixel, data + 1 to the pixel to the right of it and data + stride to the beginning of the row below the first one.
The image structure always contains calibration data and a coordinate frame that can be used to map the image to the physical world. This makes it possible to always make measurements in world units (e.g. millimeters) and to easily relate images to each other without using side channels to pass location information. For example, the exact location of a subimage within the original is always known because both images know their location with respect to the world.
Member Data Documentation
Camera calibration data.
Camera coordinate system position with respect to world frame. This frame is obtained by inverting world_frame. It is stored in the image to avoid inverting the world frame repeatedly. Use the va_image_set_world_frame() function to set both frames at once.
The maximum value a color channel in the image can take. Usually, this value is 255 for
va_gray8_image_type, but it may be less (e.g. 1 in binary images). If a 10-bit camera is used,
channel_max is 1023 even though
va_gray16_image_type would allow values up to 32767.
Note that the image may or may not actually contain this value. For example, a binary image (
channel_max = 1) may contain just zeros.
The minimum value a color channel in the image can take. With the
va_gray8_image_type, this is always zero. With other gray-level types,
channel_min can take a negative value.
Note that the image may or may not actually contain this value. For example, a gray-level image may have no black pixels.
Pointer to data (upper left corner).
Destructor function. Depending on how the image data was originally allocated, it also needs to be deallocated differently. If destroy is non-null, it will be used instead of shm_free() when deallocating a va_image.
The number of rows in the image.
The number of references to this image structure.
Pointer to source image, if this is a subimage.
The number of bytes between the starts of successive rows. If the image is compressed, stride tells the size of the compressed data in bytes.
Acquisition time in user-defined format. This field can be used to store a time stamp or a sequence index for inter-camera synchronization.
The type of the image.
The number of columns in the image.
World coordinate system position with respect to camera frame.