Understanding blob size

[Bomberofdoom]

case RECEIVING_T_PACKET:

			if(packet_buffer_index < sizeof(T_Packet_Data_Type)) // still building the packet?
			{
				// move packet character to our buffer
				packet_buffer[packet_buffer_index] = byte;
				packet_buffer_index++;
			}
			
			if(packet_buffer_index == sizeof(T_Packet_Data_Type)) // complete packet?
			{
				T_Packet_Data.mx = packet_buffer[0];
				T_Packet_Data.my = packet_buffer[1];
				T_Packet_Data.x1 = packet_buffer[2];
				T_Packet_Data.y1 = packet_buffer[3];
				T_Packet_Data.x2 = packet_buffer[4];
				T_Packet_Data.y2 = packet_buffer[5];
				T_Packet_Data.pixels = packet_buffer[6];
				T_Packet_Data.confidence = packet_buffer[7];

				camera_t_packets++;

				state = UNSYNCHRONIZED; // we're done; go back to the unsynchronized state

This is one of the switch-cases of the Camera_State_Machine function.
I'd like to understand how it determains the blob size given in the terminal so I can also use it in autonomous mode(T_Packet_Data.pixels = packet_buffer[6];, what happens in that code line).