How to scale aliased elements in Photoshop.

Question

I'm working with Photoshop for a few years now, but I've always had this problem that I didn't really understand or found a proper sollution for, I just found some work arounds...

When you create a shape in Photoshop(especially circles,rounded rectangles...curves..etc), sometimes, especially after you transform it, the edge of the shape is not full pixel, crisp and neat. It's sometimes a bit transparent or something like that. It has some sort of default Anti-aliasing or something like that...can it be turned of? Is it good to turn it of? Why is Photoshop doing that? [in illustrator for example there is that option to align object to the pixel grid, is there something like that in photoshop?]

I know that at certain sizes and twitches this does not happen, but I'm wondering why does it happen and if there are any rules to avoid this...

I also know and noticed Fireworks does a better job for this kind of stuff, but for some stuff I just love Photoshop...

have a look at this screenshot to understand what I am talking about:

Answer 1

There is no way for an algorithm to know exactly how you'd like an aliased edge to look when resized. The program doesn't know what you're trying to draw. So if you try to resize a shape with absolutely no anti-aliasing whatsoever, you may get unwanted results. This problem has been somewhat curbed with the latest content-aware updates to PS, but it has not been solved for all cases, especially interface graphics.

That being said, if you want a slightly sharper way of resizing things in Photoshop, then go to Edit > Preferences > General and set the Image Interpolation option to Bilinear. That's probably the sharpest of the ones available, but it may create accuracy issues I will warn you. Once again this is simply because the program doesn't know what you want. You may, for example, have a space between two lines before resizing and no space after resizing. The program has no way of knowing that this space is important to you, all it sees is pixels.

Answer 2

That is called anti-aliasing. It does that because most folks want that most of the time. When rescaling entire files, you can use PhotoShop's "Nearest Neighbor" method of interpolation when scaling. For scaling vector elements, I believe you set up the grid in PS to use each pixel, and then it should snap to the 'whole' pixel.

Not sure how to handle resizing of raster elements.

Fireworks does a better job at this as it was designed specifically for web graphics, so its tools are more designed for that particular task than PhotoShop's.