Patent ID: 7012872

Claim:
An image reading device for an optical disk, comprising: a detecting section for detecting the setting of an optical disc to a related location, a reading section for reading information out of said optical disc of which the setting is detected, slice level setting means for binarizing an RF signal output from said reading section at a predetermined slice level set by said slice level setting means, an adjusting section for adjusting a slice level set by said slice level setting means to an optimum slice level which is best fit for the optical disc, when the setting of the optical disc is detected by said detecting section, said adjusting section increments the slice level set by said slice level setting means from a reference slice level in steps of a fixed quantity, and a jitter detecting section for detecting a jitter of the RF signal, when said adjusting section changes the slice level set by said slice level setting means, the slice level detected when said jitter detected by said jitter detecting section is at a minimum level is judged to be the optimum slice level, when the jitter detected at the incremented slice level has a decreasing direction in quantity, said adjusting section repeatedly continues the incrementing of the slice level till the jitter changes quantity varying direction to an increasing direction, when the jitter detected at the incremented slice level has an increasing direction in quantity, said adjusting section decrements the slice level from the reference slice level in steps of a predetermined fixed quantity, when the jitter detected at the decremented slice level has a decreasing direction in quantity, the decrementing of the slice level is repeatedly continued till a quantity varying direction of the jitter is changed to an increasing direction, and said adjusting section judges that the slice level detected when the jitter changes varying direction from the decreasing direction to the increasing direction or the increasing direction to the decreasing direction, takes a minimum value, and judges the slice level detected at that time to be the optimum slice level.