Fine Print Imaging – Tech Tips

Working with the Curves adjustment layer

In the digital age, you have more control over your images than ever before. Of course with that control comes greater complexity.  So each month we are going to have an article about the various tools available to you in Adobe Photoshop.

One of the most important rules when working on a digital file is that you always want to leave the original file intact.  That means that you should create a new “editing” file separate from your original and then when you are making your edits you do so using adjustment layers when available or background copies when you’re performing a task that does not have an adjustment layer for it.  This insures if you make an adjustment and decide later that you don’t like it or it had an adverse effect you can readjust or simply throw away that adjustment layer.  You can access a new adjustment layer by clicking on the half circle icon on the bottom of the Layers palette or by going to Layer >New Adjustment Layer.

The first adjustment layer that we are going to look at is the Curves Layer. When you first open the curves layer you notice a window with a grid and a diagonal line running from the bottom left to upper right.  The bottom is your black point and the top is the white point.  Additionally if you need a smaller grid pattern, alt click for a PC or option click for a Mac inside the grid window to change the size of the squares.  On the right side you have several buttons to use.  The ok or cancel, load and save which allows you to save and load curves that you’ve made, auto that will automatically correct the file, and the options button. There are also three eyedroppers at the bottom to automatically correct the black, mid, and white points.

The curves layer is much like the Levels adjustment layer in that it gives you the ability to control the density and contrast of the file.  The biggest difference is that unlike the levels adjustment layer which only gives you control over the white point, mid point, and black point, you can make spot adjustments anywhere on the diagonal line by setting anchor points.  An anchor point is the ability to set a point on the line that correlates to the tonal value in the file that you want to adjust and moving that point up or down depending on whether you want to lighten or darken that particular value.  If you’re not sure what the tonal value is on the curve line, you can open the curves layer and then click and hold in the image and as you move the cursor you’ll see a point that moves up and down the curve line to tell you what the tonal value is.  You can also set multiple points so as to affect only a specific tonal value and leaving the rest alone.  If you want to increase the contrast of the file then you place an anchor point towards the highlight end of the line and drag it up and one towards the shadow end and drag that one down.  As you do this you’ll see that the contrast will increase. Conversely if you want to decrease the contrast place the anchor points in the same spots but move the points in the opposite direction as before and you’ll see the contrast decrease.  As you make your contrast adjustment you should see that your diagonal line will look like a gentle S curve. You do have to be careful when you use the curves layer because if you make to drastic of a S curve or move two points that are close to each other to far apart you will start to notice posterization in the file.  The easiest way to get a feel for how far is to far is to take a file and create a curve layer and place some anchor points and start adjusting them and watch what happens.  You may need to zoom into the image a little but you’ll be able to tell when you take it far.

Along with the ability to make tonal and contrast adjustments, you can also make changes to the hue or color of the file. At the top of the window where it says RGB there is a drop down menu that allows you to choose between the red, green, or blue channels. You can make global or spot hue adjustments the same way as before by placing anchor points and pulling on the curve line.

The curves layer is a very versatile tool with lots of control that can be very intimidating. The only way to learn it is with lots of practice and remember since it is adjustments layer you can always readjust or just throw away the layer and start over again without degrading the original file.  But once you do learn it you’ll enjoy the control and the result that comes from this versatile tool.