I am working through this course right now, and I am learning a lot from the exercises. Like Aurelius, I appreciate the challenge of seeking a range of possible solutions in order to match the auto grader expectations, and I also like the invitation to leave notions of grade perfection aside. However, after the joy of discovering three+ different ways to construct a solution that each match the expected output, it's frustrating that none match the target solution.

I will hold off sending an email until the end, because I may learn new ways to attack the mismatched responses as I progress. But I feel called to commiserate here, and vote for some sort of hint page for frequently-repeated "incorrect" exercises.

All that said, I am enjoying the course and I am finally learning about digital images in a deep and satisfying way!

Thanks for posting Aurelius. Yes, the autograder for the exercises in the interactive courses can be very particular about the type of solution it accepts. In this particular lesson, it was expecting the simplest possible solution. Having said that, it should have accepted your original solution as well. We are working on improving the autograder to accept multiple different solutions, but sometimes it can be very inflexible :)

If you are fairly certain of a solution and would like it to be accepted, can we request you to email wolfram-u@wolfram.com, once you are done with all the exercises? We will be happy to manually grade the exercises where the autograder refuses to co-operate and ensure that these do not stand in the way of your achieving the course certification.

Glad it worked for you. The Wolfram U team is always happy to receive feedback on our courses.

Absolutely. Please feel free to email us at wolfram-u@wolfram.com, once you are done with all the exercises. So glad to hear you found the course useful. Thank you for your feedback.