Perfect circle inside a square

Question

I need to cut out a prefect circle from a square image, sort of like this:

a circle http://h311.info/cropzor.JPG

This is pretty close but I've been using "feel" so I am not 100% sure this is perfect, meaning the distance between all 4 edges is the same.

It needs to be used with a circular gauge in a program I'm developing, so 1px offset is going to make it look terrible.

How do I achieve this? Optimally there should be 0px of "mask" (the black part) between the circle and the edges of the file.

I've used Photoshop, holding alt + shift from the center, but I did it by feel. Is there a shortcut to position your cursor to the middle of the file?

Whats the best way to achieve this?

Answer 1

Try Photoshop's magic wand tool and select the white color portion (which is circle). the tolerance property should be at 0 level. and select the circle by magic wand tool. Now use Copy command and Paste it into New Photoshop Document. Hope this work

Answer 2

You can select canvas (ctrl+a), select both layers and using move tools align horizontal and vertical center them both perfectly, then just free transform circle with shift + alt to snap to the square.

Answer 3

For Photoshop...

Draw the square.

Duplicate the square layer

In the Properties Panel set the corner rounding to 50% the width of the square for the duplicate layer.

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I'd probably use Illustrator though....

Draw the square

Copy Square

Edit > Paste in Front

Effect > Stylize > Rounded Corners...

Set the rounding to 50% the width of the square to create a circle.

Object > Expand Appearance

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Nothing actually moves with these methods so the circle will always be in perfect alignment with the square.