Using Curves in Photoshop

Using curves in Photoshop is our third and last part of Retouching Workflow tutorial. After Professional Retouching Tutorial: Healing and Professional Retouching Tutorial: Dodge and Burn.

 If you’ve ever struggled to get your head around curves adjustments in Photoshop, you found the right tutorial. We’re going to look at using different points on the curve, what they represent, and using the different RGB channels to make specific colour adjustments.

Curves in Photoshop

First, here’s what your flat, basic curve looks like before adjustments;

Using curves in Photoshop is our third and last part of Retouching Workflow tutorial. If you’ve ever struggled to get your head around curves adjustments in Photoshop, you found the right tutorial. We’re going to look at using different points on the curve, what they represent, and using the different RGB channels to make specific colour adjustments.

The adjustments curves by default

I’ve marked the curve to show what each point represents. It’s a scale that represents the starting exposure level of your jpeg or RAW conversion. the bottom left point is the blacks in your image, the top right is the whitest point and a gradual scale of everything in-between. The middle point represents the ‘mid-tones’.

If we raise a point on the curve it becomes lighter, or more exposed. Pull a point down and we decrease exposure. Clicking the middle of the curve and pulling the mid-tones up or down will lighten or darken the whole image, but will keep the black and white points where they are;

If we pull the black point higher, we lose the pure blacksIf we pull the black point higher, we lose the pure blacks;

And pulling the white point down we lose the pure whitesAnd pulling the white point down we lose the pure whites;

You can experiment to add more points, for example you can increase midtone contrast with an S-curveYou can experiment to add more points, for example you can increase mid-tone contrast with an S-curve;

We don’t just have to stick to luminosity values, we can use the dropdown menu in the Curves dialog box to affect the individual channels of Red, Green and Blue (RGB).We don’t just have to stick to luminosity values, we can use the dropdown menu in the Curves dialog box to affect the individual channels of Red, Green and Blue (RGB).

Be aware that each of these channels has a friend in the CMYK colourspace; decreasing blue will introduce more yellow for example. These relationships areBe aware that each of these channels has a friend in the CMYK colourspace; decreasing blue will introduce more yellow for example. These relationships are;

Red-Cyan
Green-Magenta
Blue-Yellow

So if we remove green, the same thing happens as if we increased the magenta curve in CMYK mode;

These relationships exist in CMYK mode of course, so if you’re working with CMYK curves for print, you can simply decrease Cyan to increase Red.These relationships exist in CMYK mode of course, so if you’re working with CMYK curves for print, you can simply decrease Cyan to increase Red.

You might see a lot of this kind of processing in magazines at the moment;

Notice how the black point isn’t completely black? And how there’s a lot of blue in the shadows? I’ll let you experiment with it.Notice how the black point isn’t completely black? And how there’s a lot of blue in the shadows? I’ll let you experiment with it.