An image coding method and apparatus considering human visual characteristics are provided. The connection system includes a fixed portion, which is fixable to said test unit, and a movable plate which is capable of receiving the electronic device to be tested and is displaceable linearly with respect to said fixed portion between two positions which correspond respectively to a connection position and a disconnection position of the electronic device, by manually actuated displacement. The mapped image layers of a tile may be provided to a shader module, such as a pixel shader, to composite the image layers into display data. The blocks may be arranged in a running bond, such that the vertical seams of one course are offset from the vertical seams of an adjacent course. The negative acknowledgements thus indicate failed receipt of data.