photoshop - What is a "Slanted S" in a curves layer?

I am trying to do a Photoshop tutorial, seems easy, but I can't understand one phrase: `First, I add a curves layer and create a slanted S. What does slanted S mean? Maybe I should "write" S in curves editor?

P.S. The tutorial is big, and you can use Ctrl+F to find an occurrence of this words in the text.

I just don't understand the meaning of "Slanted S". It's just my assumption that it means draw an S-shaped curve.

Answer

Use 2 points to create an 'S' shape in the curves editor.

See: http://www.chromasia.com/tutorials/online/curves/images/basic_s_curve.jpg

So basically the curves editor is a chart. For each pixel in an image, its brightness is represented by a number from 0 to 255. 0 is pure black, 255 is pure white, and everything in between is a shade of grade gray.

This works in color too because images have 3 channels of color red, green, and blue, and each of those will be 0-255. This is why you can apply curves to all channels at once, or red, green, or blue individually.

So, what does the curves actually do? By default, nothing. You start with a straight line on the chart, where every input is the same as the output. 0 is 0, 128 is 128, and 255 is 255. When you change the line, you are changing the output for any given input.

So, in the link I sent you can see that the input is 144 and the output is 189, this means when photoshop sees a pixel with a value of 144, it raises the output (brightness) to 189. Because the line is curved, everything around it is affected too, though becoming less affected as it gets farther away from your point.

So in a nutshell, for an s curve, you create 2 points, one in the highlights where you make bright pixels brighter, and one in the shadows, where you make dark pixels darker, while values in the middle remain mostly unaffected. This increases overall contrast in a pleasing way.

Hope that helps a little more.