Image reproduction speed conversion apparatus

An image reproduction speed conversion apparatus, for converting first image data to second image data having a scanning cycle different from that of the first image data, to which a write-in timing signal and a read-out timing signal are input from an external source, said apparatus comprising:

• memory means for storing image data, to which the first image data is written in sequentially on the basis of the write-in timing signal, and from which the second image data is read out sequentially on the basis of the read-out timing signal;
• surpassing-detection means for detecting that the read-out timing of said second image data during a relative next time period comes before the end of writing of the first image data during a relative present time period, to output a first surpassing-detection signal, and for detecting that the write-in timing of said first image data of the next time period comes before the end of reading of the second image data of the present time period, to output a second surpassing-detection signal;
• and
• surpassing-processing means for inserting said image data into the second image data on the basis of the image data stored in said memory means in response to the first surpassing-detection signal output during the term corresponding to an effective scanning line of the second image data, and for thinning out said image data from the second image data in response to the second surpassing-detection signal output during the term corresponding to the effective scanning line of the second image data, said surpassing-processing means further comprising:
• processing means for selectively inserting and thinning-out said image data;
• and
• prohibition means permitting a predetermined signal to prohibit inserting and thinning operations of said processing means during the term other than the term corresponding to the effective scanning line of the second image data.