You didn't present some context on how you reached this content on the website. It looks as if it was an exercise to produce a shader detecting edges based on derivative functions or just sampling neighboring texture pixels.
How would you improve description of this challenge? As you can notice, we provide a lot of hints, description etc. for other challenges, but this one is vague on purpose.
Thank you
1) Make it clear that the lack of instructions is intentional
2) Have a "pixel inspection" tool so we can check the exact RGB values in the expected and diff images more easily.
Thank you!