How to create a PNG image that is only a byte

We've seen PNG images on the web that are less than 1kb. When I create a new blank PNG in Phot开发者_如何学Pythonoshop, its size is about 20-30 Kb :(

For example, I've seen a 100*10 px PNG that was only 90 bytes!

Which Apps can generate these? Do you have any tips?

After fvu's answer: plz tell me what optimizer is better than other?

There no reason a minimal png should be that big. Check out png optimizers like this one or this online tool should Photoshop not include such a tool. Google knows about even more PNG optimizer tools.

Edit: a 10*100px png floodfilled with red measures 143 bytes optimized with Paintshop Pro's integrated PNG optimizer. Apparently it can be made even smaller than what Paintshop manages :-)

Edit based on OP's comment: Corel Paint Shop Pro is a photo editor, I guess you can call it a lightweight alternative to Photoshop. It was the quickest way for me to create a png comparabable to op's example.

As for what optimizer is best: some good old fashioned testing and comparing should tell you a lot, I wouldn't be surprised to see that the performance of individual optimizers depends on the input characteristics - eg some will do better on photos than others but on computer imagery it's the other way around, based on the algorithms used.
Aside from the compression ratio the ease with which you can integrate the optimizer in your workflow should be considered quite important.