Size of data field in TangoImageBuffer

Question

I am trying to do a memcpy of the TangoImageBuffer data field, which, if the image is YUV, according to me should be (buffer->width * buffer->height * 3 * sizeof(uint8_t)) (sizeof just for kicks, I know it is 1), but this makes it segfault. if I just copy height*width bytes it works, and also with height*width*2, I do seem to be getting valid data, I just don't know which size should this field be.

My (relevant) code:

void onImageCallback(void *context, TangoCameraId id, const TangoImageBuffer *buffer)
{
  memcpy(img_struct->image_buffer->getBuffer(), buffer->data, buffer->width * buffer->height * 3 * sizeof(uint8_t)));
}

Where image_buffer is a java ByteBuffer wrapping class which I am using in C++, inside it is allocating memory by calling new with the specified size (which in this case is the same I am trying to memcpy), and a jobject reference by doing a env->NewGlobalRef(env->NewDirectByteBuffer(buffer, this->bufferSize));, where this->bufferSize equals (buffer->width * buffer->height * 3 * sizeof(uint8_t))

I am pretty sure it is allocating the right amount of memory, as I have used it also for memcopying the xyzij buffer in other function (with the correspondent size difference, as those are floats) and it works just fine (yet I have also tried overallocating), so I know the problem is not the destination being too small.

In case this information might add to the question, I am using the regular color camera, so height should be 1280 and width 720 if I recall correctly.

Edit: Upon manually looking for the maximum amount of data I could copy without getting the segfault, it seems it tops on 1384448 (i.e. that works, 1384449 segfaults), which is roughly 1.5 times the size in pixels of the image, adding to my confusion.

Answer 1

The pixel format is documented as YV12 aka YUV420SP. It has full resolution for Y with 2x2 subsampling for U and V, thus U and V both have 1/4 as many samples as Y. The total number of samples is then width*height*(1 + 1/4 + 1/4) = 1.5*width*height.