1. An image forming apparatus comprising: a correction unit configured to correct image data based on a correction condition; an image forming unit configured to form an image based on the corrected image data; an image bearing member configured to bear the image formed by the image forming unit; a transfer unit configured to transfer the image on the image bearing member to a sheet; a measurement unit configured to measure a measurement image on the image bearing member; a conversion unit configured to convert a measurement result of the measurement image by the measurement unit, based on a conversion condition; a first generation unit configured to generate the correction condition based on the measurement result converted by the conversion unit; an obtaining unit configured to control the image forming unit to form a test image based on test image data, control the measurement unit to measure the test image on the image bearing member, and obtain a measurement result of the test image by the measurement unit; a controller configured to control the image forming unit to form a test image based on test image data, and control the transfer unit to transfer the test image formed on the image bearing member to the sheet; a reception unit configured to receive a user instruction based on a result of a user having compared a sample image and the test image transferred on the sheet; and a second generation unit configured to generate the conversion condition based on the user instruction and the measurement result obtained by the obtaining unit, wherein the sample image includes a first sample image, a second sample image, and a third sample image, a color difference between the first and second sample images is smaller than a threshold value, a color difference between the second and third sample images is larger than the threshold value, density of the first sample image is higher than density of the second sample image, and the density of the first sample image is higher than density of the third sample image.