Do you consistently use Ancestry to access census records? Or, do you at times use FamilySearch or other sites? I have to admit that I rarely venture out of Ancestry to update my census research. However, I have heard other researchers recommend looking at a census record from different sources.
While updating my source citations for Mary Wells, daughter of Benjamin Franklin Wells, I was looking for her in the 1870 census. Since Mary wasn’t listed with her father’s family, I pulled up my old notes to try and figure out where she was living.

This information combined with a search for Alice Wells living in Calhoun, Michigan helped me do a simple search of the 1870 census record.

Unfortunately, when I opened the image for the household containing Alice and George Wells, the census record was barely legible.

Even using the tool to INVERT COLORS, the census record is still hard to read.

That’s when I remembered the advice to check other sources for census records. When I located the Doolittle / Wells household on FamilySearch site, I found a version that is slightly easier to read.

However, the FamilySearch site has a tool that Ancestry doesn’t.

This ADJUST IMAGE tool allows one to change the brightness and contrast. When I played with those settings, I was able to make the image more legible.

Now, I understand why professional researchers suggest looking at census records on multiple sources. If I had not looked at other sources for the census record, I would not have found a legible version that supports my handwritten notes.
Yep – not only does FamilySearch have this tool, so does FindMyPast – I do the same thing you do if an image on Ancestry is close to illegible 🙂
I’ve noticed that Ancestry appears to have brightened digitized census images across the board. As you pointed out, it is much easier to work with FamilySearch images.