Image forming apparatus having controller for switching thresholds for deciding amount of color misregistration

An image forming apparatus that forms an image on a sheet, the apparatus comprising:

• an image bearing member configured to rotate;
• a plurality of image forming units configured to form color images, each having a different color, on the image bearing member;
• a sensor configured to detect color patterns formed on the image bearing member by the plurality of image forming units, the color patterns being used for detecting color registration;
• a comparator configured to compare a detection value corresponding to a detection result by the sensor with a threshold, and to output an output value according to a comparison result;
• and
• a controller configured to control the plurality of image forming units to form color patterns, to control the sensor to detect the color patterns, to set the thresholds that correspond to the color patterns, to control the color registration according to the output value from the comparator,
• wherein the color patterns include a first color pattern of first color and a second color pattern of second color that is different from the first color,
• wherein the second color pattern is formed at an upstream side of the first color pattern in a rotational direction of the image bearing member,
• wherein the first color pattern is adjacent to the second color pattern,
• wherein the controller sets the threshold to a second threshold that corresponds to the second color pattern based on an edge timing of the output value that is output from the comparator according to the comparison result between the detection value corresponding to a detection result about the first color pattern and a first threshold corresponding to the first color pattern.