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Taking Photoshop’s Curves Beyond Highlights and Shadows

How To, Resources, Web Design | Jun 22, 2010

Photoshop’s Curves is a flexible control that can brighten or darken parts of a layer based on the layer’s luminosity.

Editing tones in an image—not just grays and not always photos—can do more than fix highlights and shadows.

Curves can be used to edit photos, masks, graphics and even hues. But using it requires a little know-how and imagination.

Read on for more details about what Photoshop curves are, as well as how to use them properly for your designs.

As usual, feel free to leave us your comments at the end of this post.

 

Making Tonal Adjustments

Curves is found near the top of the Image → Adjustments menu. Its most obvious use is to adjust contrast in an image, and it is intuitive enough that most users need to study it only for a minute or so before catching on.

examples of simple tonal adjustments

Above: Drag a point on the curve line up to make the image brighter and down to make it darker. But what does that mean?

Curves uses a grid that shows before and after. The horizontal axis indicates original tones, and the vertical axis indicates how they will change. A diagonal line bisects the grid. Dragging points away from the diagonal line will brighten or darken highlights and shadows depending on where the change happens.

diagram of Curves grid, before and after

Above, the curve turns shadows into bright highlights, muddies mid-tones and turns the original white point into middle gray. The further the curve moves away from the diagonal line, the more extreme the change will be. It also means that the angle of the curve changes the image’s contrast in a given range of tones.

examples of how the slope affects contrast

Above, blue denotes which tones most of the pixels use. Red denotes the slope.

  1. Most of the tones are just to the left of mid-gray, so creating a steep angle in that area would give most of the image more contrast.
  2. The opposite—giving the mid-tones a flat slope—lowers the contrast.
  3. Creating a steep slope away from the popular tones creates extreme contrast: many shadows, some highlights and few mid-tones.

 

Choose Tones to Change With Curves

Unlike Levels, Curves allows changes to a select range of tones. Not only can shadows, mid-tones and highlights be changed, they can be changed independently.

examples of selective tonal changes

Two variations on the photo above show how Curves can affect different areas. In the center photo, pixels brighter than 50% are all brightened. But only the highest highlights—and darkest shadows—are brightened in the right-most image.

To add a point to the Curves line, simply click the line. To remove a point, drag it off the grid.

The Curves control isn’t limited to photos. For example, the logo below has a subtle texture—but what if “subtle” isn’t the right look?

example of a logo with more contrast via Curves

Above, a change in Curves brings out the texture in the disc and amplifies the sheen on the bolt. Knowing that Curves can be used beyond fixing tones and can be used in photos is the first step to grasping its hidden features.

 

Playing With Color

The Curves control hides many features in plain sight. One of these is the ability to color-correct (or cross-process) any digital image.

illustration showing where the RGB options reside

Above: with a drop-down menu above the grid, the user can edit one channel (red, green or blue in RGB images) at a time.

example of using Curves alter a photo's color

The photo above was given a color cast by warming its shadows and cooling its highlights. Specifically, red is removed from the shadows but added to the highlights, and vice versa for blue and green.

example of using Curves to tint a photo

A grayscale version of the same photo becomes a duotone when we use Curves to adjusts its channels. Above, extra red and green warm the highlights and mid-tones, while the shadows take on a bluish tinge. In Curves, channels often don’t require major changes to alter an image dramatically.

 

Improving Selections

Selections and masks in Photoshop aren’t simply on-or-off features, but rather a range of values—much like a gradient. And masks, like gradients, can be manipulated with Curves.

step-by-step 1

We want to screen the red image behind the black text but leave details at the edges. We start by adding a mask to the photo with the layer (above). A layer mask controls the layer’s opacity without erasing its pixels.

step-by-step 2

With a reflected gradient, the mask hides the center of the photo. In layer mask terms, light means more visible and dark means less visible.

step-by-step 3

We make the gradient “shallow” using Curves. If white areas of a mask are visible and black areas are invisible, then the gray is somewhat hidden.

step-by-step 4

The result (above) is a photo that is screened behind text but still visible at the edges. However, the text is still difficult to read.

step-by-step 5

Every time Curves opens, it looks at the mask anew. Above, we lower the white point to make the mask darker and thus less visible.

step-by-step 6

The result is a gently screened photo that fades into the text (above).

 

Secrets of the Curves Control

Curves is full of shortcuts and hidden features. Here are a few useful tidbits:

diagram of hidden features in Curves

Still, the fundamentals haven’t changed since Photoshop 1.0 first arrived on the scene. Many possibilities arise from this simple control.


Written exclusively for Webdesigner Depot by Ben Gremillion. Ben is a freelance writer and designer who solves communication problems with better design.

Do you use Photoshop’s curves in you designs? What for and how they impact your design?

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  • http://iamjpg.com/love iamjpg

    Good hints but only useful in photography, practical wise.
    Webdesign wise, Improving Selections wise it should easily just be a smooth edged rectangle at some opacity for clean and minimal sake.

  • http://www.blende5.ch Lukas

    Nice post. But I think this are basics…

  • http://www.gwozdek.com Michal

    I would like to see more articles like this, please! :)

  • http://www.pscyhed.be/wordpress Darkened Soul

    Always hot stuff to play around with these goodies. fun fun fun ;)

  • rishi arora

    very useful. now i can finally use curves with confidence.

  • http://www.jonbevan.me.uk Jon

    That’s actually very useful! Thanks very much – I’ve always wondered what the purpose of that little graph was and how to use it properly :)

  • Susan

    This is THE best explanation of the curves feature that I have found. I finally get it. Thanks!

  • volkan

    Thanks : ))) great job !!!

  • http://www.jordanwalker.net Jordan Walker

    Great PS tips and tricks.

  • http://www.litup.com evan

    great article; thank you very much!

  • http://stylishwebdesigner.com/ Tanya

    Amazing work . I love these kind of articles. Curves is a useful tool I knew that but now I get to know that its more more more useful

  • http://freshbusinesscards.com psd business cards

    Very nice tips, thanks !!!

  • http://www.benstokesmarketing.co.uk Ben Stokes

    Very nice tutorial . . this will defiantly come in handy, the before and after grey scale curves is a great resource.

  • yael miller

    Here’s another tip: you can use Curves to control the quantity of ink in a CMYK blend overall within an image.

    For example, if you want to reduce black within a photo to prevent muddiness in a newsprint color ad, select ‘K’ from the drop-down menu and drag the bottom left corner of the diagonal line towards the right on the X axis, until you see the overall ‘blackness’ within the image drop. You can do the opposite (increase the color) by dragging the corner upwards on Y axis.

    You can do this with any color to reduce its dominance in an image. There are other tools that allow you do this in Photoshop, but I find Curves to be more powerful and flexible with this kind of thing.

    Good article!

  • http://www.indianic.com Piyush Parmar

    nice post… can do many things now with much easier way… cheers…

  • http://www.crearedesign.co.uk/ Jarkko Sibenberg

    Thanks for the guide. It’s nothing new really, but a good overview of the curves tool. I’m sure next time I’ll feel more confident using it since I’ve made similar things in a more complicated and less flexible way. Well explained, and those little images are very informative.

  • http://www.thomascraigconsulting.com Thomas Craig Consulting

    Nice tips, great for a newbie or someone that has forgotten the basics.

  • http://www.gmstop.com/ Jocuri online

    Nice tutorial, i want more articles like this man.

  • http://www.michaelsaathoff.com Michael Saathoff

    great post, i hadnt really used this much so i foresee this article coming in handy! thanks

  • Danica

    Nice Tut…

  • http://newstopf.com/ NewsTopf

    … usefull tips, not only for beginners. Thnx!

  • http://www.mblogphotuz.blogspot.com M Blog Photuz

    Photoshop curves is a tricky thing and it’s very helpful to my blog cause I convert in more easier to understand in easy way to others, I’m waiting for more tips!

  • http://http://www.paolalozano.com.mx paola lozano

    truly useful :D

  • http://www.4over4.com/shipping-labels.html Labels Fan

    Thanks for this tutorial. I knew some about curves because of other tutorials that use this tool for a small part. Since then I’ve been just moving the curve up or down until I feel light is good. In here I can see how to start using the points and that there are more things you can do! Thanks.

  • Adam

    Very useful! Thanks a lot!

  • http://molecularia.blogspot.com NicoP

    Excellent article indeed, thank you very much! It is the best explanation of the Curves tool that I ever bumped into (and be sure that, being an enthusiastic amateur, I have searched a lot for a decent tutorial on this subject).
    Just a question. On the section “Playing with color”, related to the first Before-After on the man holding a camera, you said: “Specifically, red is removed from the shadows but added to the highlights, and vice versa for blue and green.” I can’t get it, it seems to me that shadows are getting warmer (more reddish) and highlights are colder (blue-greenish). Could you please explain me this?

  • vico

    You tutorial is goes right to the point with a pristine clarity. They way you explained the histogram and the curves is just so didactic that even a beginner like me can understand the whole concept. I thought that it would take me a lot of more time to understand this topic, but thanks to your altruist work I now comprehend curves quite well. Thank very much.

  • http://www.etatvasoft.com Rakesh

    For second example, I believe, a mask layer and feather can provide same result. However, its a good example.