Author's note: this tutorial was originally written for auditorial.com a site showcasing Elemedia speech compression technology that was incorporated into the Netscape Media Server and Player. Auditorials were audio tutorials consisting of audio voiceover with an onscreen slide show that was cued to various points throughout the audio presentation. Looking back on it today, Auditorials are interesting because they are really forerunners to Web-Based Training and pod-casts — 10 years before their time. The following article is adapted from the script of the Auditorial.

Enhancing your Digital Images with Photoshop's Adjustment Layers

By Bob Schmitt
June 22, 1997

Adobe Photoshop's greatest strength is its wide variety of image correction and enhancement tools. Prior to version 4.0, applying corrections such as changing hues or adjusting the black point meant changing the actual pixels of the image. Of course, if you weren't happy with your adjustments it meant you had to revert back to a previous version and start over. Now with version 4.0's Adjustment Layers feature, you can make these corrections and enhancements independent of the image, or portion of the image, that you are editing. Adjustment layers work as an overlay to the image — a filter if you will — that is applied to the pixels of the image only when the layers are flattened or merged together. Adjustment Layers can easily be turned on or off in the layers palette.

In this tutorial, you'll learn how to use adjustment layers to enhance your digital or scanned photographs for use on the Web. Though I'll show specific settings for different techniques, every image is different and requires different settings determined by your unique artistic eye.

Here is a scanned image of my daughter Hayley standing in front of the Wisconsin state capitol in Madison. I scanned this image on an inexpensive, low-end desktop scanner, the type which many of us poor, starving designers are reduced to using. The image on the left is the raw scanned image, on the right is my final corrected version. So, how do you get from the image on the left to the one on the right? Let's start by looking at the initial scan.

As you can see, the scanner did a very poor job of capturing crisp whites and deep solid blacks. It appears as if the whole image has a hazy, grayish quality. We'll fix this by correcting the images overall levels.

Let's start by making a new adjustment layer. Select New Adjustment Layer from the popup menu at the top right of the Layers palette. In the New Adjustment Layer dialog box you can choose the type of adjustment you would like to make. Your options are: levels, curves, brightness/contrast, color balance, hue/saturation, selective color, invert, threshold, and posterize. In this case we'll choose levels.

The other settings in this dialog box let you set the opacity and ink mode of an adjustment layer — which can create some interesting effects. The final option lets you group the adjustment layer with the preceding layer. This is useful if you have several image layers in a file and want the correction to affect the layer, or group of layers, directly below it and no others. These three options can also be set after-the-fact in the layers palette — so there's no need to worry about them now.

We want to do an overall correction, so we'll keep the settings at 100% for opacity and normal for mode.

After clicking OK, you'll see the levels dialog box. This is the same levels dialog box you would get if you chose Adjust/Levels from the Image menu, the difference here is that the adjustment is applied as an overlay and not directly to the pixels of the image. Notice how the levels are compressed into the middle, with wide gaps between the black point on the left and the white point on the right. This is the cause of our sickly looking scan. We'll use the levels eyedroppers to quickly correct this.

Here's a tip in using the eyedroppers: when I scanned the original photograph, I included a gray strip with the image. A gray strip is merely a strip of neutral grays from black to white in 10% increments — gray strips are available at most photography shops. This strip gives you a control image that helps you see what the process of scanning has done to our original image. In this case, you can see that the black square is at about 95% instead of 100% black, as it should be. We can correct this by selecting the black point eyedropper in the levels dialog box and clicking in the black square of the control strip. At this point you can see that the levels have shifted toward the black point making the black portions of the image darker and adjusting all the other levels accordingly. Conversely, you can see that instead of nice, pure whites we have roughly a 10% gray. Let's correct this using the white-point eyedropper, and clicking in the white box of our control strip. Now, repeat the same procedure for the mid-point eyedropper, clicking on the 50% box of the control strip.

Now, as they say on the cooking shows, all great chefs season to taste. And you'll do the same with your images, adjust the levels until they look good to you. In this case I want to lighten and brighten the image overall, so I'll move the mid-point slider just a little more to the left. There's no exact science at work here, I'm just making it pleasing to my eye.

Now let's make the image a little more juicy. We'll use another of Photoshop's image editing features, Hue/Saturation, to pump up the saturation of the colors in the photo and give it a nice, rich feel, taking full advantage of working in the RGB color space.

Create a new adjustment layer, this time selecting Hue/Saturation from the type menu. In the Hue/Saturation dialog box, you can adjust the hue, saturation and lightness of the image. I'm pretty satisfied with the overall hues in the image, so we'll leave that at 0, but we will pump up the saturation by pushing the saturation slider to the right until we get nice, juicy color overall. Again, season your images to taste.

Once you've built several layers of adjustment there may be a situation where you want to make changes in one of the previous adjustment layers. For example, after adjusting the saturation, I'd still like to lighten the middle values of the image a touch. I can do this by double-clicking on the layer called "levels" in the layers palette. This brings up the levels dialog box. Now, I simply make any corrections that I wish.

Alright, now we've got our image looking much better, but I'm still not quite satisfied with the cyan sky color. Although that's the way it looks in the original photo, I'd like a much richer, more polarized-looking sky. We can accomplish this with adjustment layers as well.

In addition to making overall corrections, with Adjustment Layers, you can also make selective adjustments. In this case, we'll make a selection of the sky and use a hue adjustment to alter its color. To make the selection, choose Color Range from the Select menu. This brings up the Color Range dialog box seen here.

In this dialog box, we'll quickly select the sky using the eyedropper tool and clicking in the blue area of the sky. In the preview window, you can see the selection represented as a black and white mask. The white sections of the mask are the "see-through" sections — this is where our adjustment will take place. Black areas of the mask will be protected — or masked off — from the adjustment.

You can click around the sky until you get what you think is the ideal sample point for the selection. Next, adjust the fuzziness slider. The fuzziness of your selection determines the tolerance — or range of colors — on the darker or lighter side of the color that you sampled with the eyedropper. In the case of this image, I adjusted the fuzziness until I got good separation of black and white between the sky and the capitol building. Once you have your ideal selection, click OK.

In the process of using Color Range, I've selected more pixels than I had intended. For example, I don't want to change the hue of Hayley's dress, so I'll edit the selection using Photoshop's Quick Mask feature. The quick mask allows you to see and edit the selection as a graphic overlay. You can then quickly select the area that you want to exclude and fill it in, thereby eliminating it from the selection. Clicking on the Quick Mask icon in the tools palette gives you a graphic representation of the selection which we can now edit. We'll use the Lasso tool to quickly select the area of Hayley's dress and, holding down the option key, hit delete. This fills the area with the black foreground color. Click on the selection icon to the left of the Quick Mask icon to return to normal view.

Now we'll make another new adjustment layer, again choosing Hue/Saturation. This time, instead of changing the saturation level, we'll change the hue by moving the slider to the right. A tip for getting just the right hue, is to use the Sample box underneath the Lightness slider. Sample a color from the image by clicking on the image in the area you want to alter — in this case the blue sky. The color you select will appear in the Sample box. It's an easy matter then to move the Hue slider around until the Sample box matches the exact hue you desire. Of course, if you have the preview checkbox selected, the change will show up in the image, but only if you let go of the mouse. The sample box will update dynamically as you drag the slider back and forth, enabling you to quickly find the color you need.

After clicking OK in the Hue/Saturation dialog, you'll see a thumbnail representation of the selected area of the image in the layers palette. You can make alterations to this selection, at any time, causing a change in the hue adjustment — or, if you want, delete it completely by throwing the adjustment layer in the trash. Try doing that without adjustment layers! You can't. In previous versions of Photoshop, to alter an adjustment like this after-the-fact, you would have had to revert to a previous version of the image (assuming you saved a previous version) and start over. In Photoshop 4.0 altering the selection is as easy as using any of Photoshop's drawing or selection tools. To edit the selection, simply option-click on the thumbnail in the layers palette. Now, you can use any of Photoshop's paint or selection tools to alter the mask.

You should now have a good idea of how Photoshop's new Adjustment Layers feature can help you quickly enhance the look of your digital images, as well as save you a great deal of production time. Although we've only just scratched the surface of adjustment layers, I hope this helps launch you on your way to greater flexibility and experimentation with your photos. Happy cooking!