| 摘要 |
PROBLEM TO BE SOLVED: To form a stable half tone image whose density is not influenced by temperature and humidity by previously preparing a temperature and humidity detecting means and plural threshold matrices, properly selecting the threshold matrix in accordance with the detected value of the temperature and the humidity and controlling how to assign the tone expression number of a threshold per pixel in the threshold matrix. SOLUTION: A temperature and humidity sensor 515 detects ambient temperature and ambient humidity on the inside of an image forming device and transmits a signal (x) to a control part 520. A tone expression number changing means 521 provided in the control part 520 generates a selection signal A for changing how to assign the tone expression number of the threshold per pixel in the threshold matrix in accordance with the detected value from the sensor 515. The generated selection signal A is transmitted to a threshold memory 512. How to assign the tone expression number of the threshold per pixel is changed by selecting the threshold matrices 512a and 512b based on the selection signal A. |
