An image forming apparatus that enhances measurement accuracy of a pattern image and improves quality of a printed image. Light emitted from a light emission unit based on a first measurement condition is reflected from an image bearing member, and first information is generated based on a measurement result of the image bearing member. Second information is determined based on the first measurement condition, the first information, and a second measurement condition. Light is emitted based on the first measurement condition when a first measurement image is measured, and an image forming condition is generated based on a measurement result of the first measurement image and the first information. Light is emitted based on the second measurement condition when a second measurement image is measured, and the image forming condition is generated based on a measurement result of the second measurement image and the second information.