To provide an image reader in which a high quality image signal can be obtained even if an ineffective pattern, such as the base of a negative film or a bright spot in the image of a positive film, exists in a read area, a medium storing a control procedure of the image reader and a data structure for transmitting a computer program signal including the control procedure of the image reader while encoding.

Using a light receiving element having an overflow drain mechanism and based on the brightness information in the read area, exposure conditions are set such that the exposure quantity at a brightest spot by a reading light passed through or reflected on the brightest spot of an effective pattern to be represented by gray scale be equal to or close to the quantized maximum exposure quantity of the light receiving element. The effective pattern can be represented over the entire or substantially entire region of the dynamic range of the light receiving element and oversaturation due to an ineffective pattern can be suppressed by the overflow drain mechanism.