Photoshop’s Layer Stacks

Using th Wrong Tools for the Right Reasons

By Dan Burkholder Back to


If you’ve ever mixed a can of paint with a screwdriver, you know there’s something innately satisfying about using the wrong tool for the job. Perhaps this illogical feeling of satisfaction harkens back to our days as primitive beings, when a thighbone could both kill our prey and stir the succeeding meal. This gratifying rebellion can be claimed in Photoshop too. I found that there were multiple tools we could misuse in our quest for image control and creative discovery.

One of my more recent discoveries is that HDR processing can be used creatively. I’ll also cover using the Stacks feature in CS4 here, again in a not-so-usual way. Call it creative freedom or call it fun, but, whatever moniker you choose, I think you’ll enjoy how we can playfully misuse some of Photoshop’s most powerful tools to create images with a charm and intrigue all their own.

In the classic darkroom, we’d mix exotic concoctions that changed the development characteristics of film or paper, toned our prints in new and seductive fashion, or simply reduced our wash time with a home-brewed hypo-clearing potion. There was an element of joy as we mixed our chemistry to get better (or different) photographic results. We’re now striving for that same digital moonshine in Photoshop. For example, in a recent issue of PHOTO Techniques, I outlined how we could use Photoshop’s Unsharp Mask filter to enhance local contrast in our images.

Figure 2. Disparate images merged to HDR.


Figure 3. Settings used for the HDR combination.

Figure 4. Warping to correct sagging hotel.

Figure 5. Final version of old hotel and leaves.

Though we won’t be using bracketed sets of images here, you still want the best group of images to combine in this creative workflow. If you’ve captured your images as Raw files, first use Adobe CameraRaw (or any other Raw converter you prefer) to adjust your images like you normally would. Color balance, noise reduction, retouching, correcting chromatic aberration and—now with CS4, your local contrast and color—can also be adjusted. Don’t make the mistake of thinking that your subsequent steps will compensate for poorly exposed and processed Raw files.

Disparate HDR

By “disparate HDR” I mean that we’re going to deliberately misuse Photoshop’s Merge to HDR function to combine— not a bracketed series of the same scene—but two or more completely different images.

If you’re a regular reader you’ve heard me praise the workshop students from whom I’ve learned much over the years. Sure, I’m the instructor, but I’ve found that dedicated photographers (both professionals and amateurs) have a long tradition of openly sharing their tips and techniques. For this article’s subject, I owe a special thanks to Lucien Flotte of New York City. After taking one of my HDR workshops at the International Center for Photography, he made a “happy mistake” by combining images that had no business being in an HDR workf low. Many of us have made similar mistakes, but it took an inquisitive soul such as Lucien to see the creative potential in the blunder.

For this first example, we’re combining a shot of an abandoned hotel with a closeup of fall leaves and pine cones on the forest floor. Figure 2 shows Bridge with the two images selected. When we combine the hotel and leaf images as illustrated, Photoshop builds a 32-bit image that is lush with tonal potential from shadow to highlight. I’m not going to illustrate all the Merge to HDR steps since they’ve been covered in previous articles. I will provide the settings I used in my favorite HDR processing plug-in (from, which has helped legions of photographers tackle HDR better than with Photoshop alone. Figure 3 shows the ToneMapping dialog box with the settings I used.

It’s not the lens’s fault

That bowing of the hotel siding (Figure 3) is not barrel distortion but rather the old hotel itself bowing as it sinks and sags on its way to collapse. Figure 4 shows how I’ve used the Warp transformation to pull up the two corners of the hotel.

Jumping to the chase, Figure 5 shows the final combined image. And yes, I used a few adjustment layers to tweak the color and contrast. I really like the way the HDR process melded the best midtones from the two completely different captures. If you do this enough, you start to get an intuition about how the two (or more) images will merge. There will always be an element of surprise. It’s a lot like how we’d sandwich two negatives in the enlarger to print on silver gelatin paper. You could sorta have a feel for the way the print would look, but until you actually printed it and saw how the two negatives’ densities worked in concert, it was impossible to accurately predict the look of the final print.

Note: the images you want to combine must be exactly the same size. That is, the height and width of all images must be the same. Even one pixel difference and the process won’t work. Should you violate that rule by attempting to merge two or more images that vary in pixel dimensions, you’ll get an impolite message like that in Figure 6.

Merging same-exposure images

What about using HDR merging in yet another nonstandard way? If we can use it for images that are completely different in subject, composition, or color, we can certainly use it to combine three identically exposed images of the same subject. Why would we do this, you ask? If you’ve read any of my previous articles in PHOTO Techniques, you know that waterfalls are a dime a dozen here in the Catskills of New York State. In this example, I photographed a waterfall using the lowest shutter speed I could achieve given the lighting. The 1/6-second shutter speed didn’t give the angel-hair quality in the water that I sought (Figure 7).

Not having a neutral-density filter, I instead did something new. With the camera firmly mounted on a tripod, I exposed three identical frames of the falls. Figure 8 shows these frames in Bridge. Though you can’t tell in this small screen-capture, the flowing water is obviously slightly different in the three exposures.

Here’s where it gets fun. Let’s use CS4’s HDR capabilities (along with a helping hand from some third- party software) to create an image with beautifully smooth, yet textured, water.

HDR usually involves combining a series of bracketed exposures. When you combine a group of images that have the same exposure, you might be confronted with the dialog box in Figure 9. This Manually Set EV dialog box gives you an opportunity to set the shutter speed, aperture, and ISO for the images in your series.

There is no need to fabricate your shooting data; just check your metadata in Bridge and type it into the text boxes. Once you’ve entered the same info for all of your images, the OK button becomes active. Clicking OK signals Photoshop to process your images. Remember, if you are merging disparate images, odds are they already have different shutter speeds, apertures, or ISOs, so you won’t be interrupted with the Manually Set EV dialog. In this case, all three waterfalls shots were identically exposed so I did have to deal with the Manually Set EV dialog. The final three identical-yet-merged-together images are shown in Figure 10.

Now let’s look at CS4 Extended’s Stack Mode feature and how we can use it too in an unconventional but-oh-so- neat approach.

Figure 6. Photoshop’s image-size alert.

Figure 7. Single capture of falls.


Figure 8. Three identical exposures in Bridge.

Figure 9. The Manually Set EV dialog box.

Figure 10. Final falls image after merging three identical exposures.

CS4 Extended power

If you are blessed enough to own the Extended version of CS4, you can create adjustment layers with 32-bit images. (CS4 Standard users will find their Layers menu is completely inoperative with 32-bit images.) This lets you perform additional operations on your super-thick 32- bit image (with billions of tones per pixel). Sadly, my very favorite adjustment layer—Curves—is disabled, even with CS4 Extended. Yep, Curves cannot be applied as an adjustment layer, even though you opened your wallet even wider for the more expensive version of Photoshop. Oh well, maybe with CS5…?

But don’t get discouraged. Many of CS4 Extended’s features are designed for the scientific community and the 3-D rendering crowd. But as honest-to-goodness photographers, we can mine some amazingly useful and creative effects from CS4 Extended if we know where to look.

Stack mode is present in both the Standard and Extended versions of CS4, though it’s easier and more fun in the Extended version. Let’s look at an expected use of the Stack Mode and then—of course—we’ll experiment with an unexpected way to use this amazing new feature of Photoshop.

Image Stacks are two or more images (usually of the same pixel dimensions) that are combined into a Smart Object from their former life as separate layers. This Smart Object can then be subjected to various mathematical formulas via the Stack Mode command (Layer > Smart Object > Stack Mode). Some uses include noise reduction (Mean or Median modes) and elimination of objects that moved between successive captures (Median). Other modes are pretty much reserved for the scientific community or the very creative or very nerdy (Entropy, Kertosis, or Standard Deviation).

Figure 11 shows CS4’s Scripts menu, which builds a Smart Object in a unique way.

A typical statistics job

After executing the above menu command, you’ll face the Image Statistics dialog box, as in Figure 12. Here’s where you make the all- important decision concerning Stack mode. Though I’ve used Median for both of the examples below, there’s no reason you can’t have a delightful time exploring all the other modes with intriguing names like “Kertosis,” “Entropy,” and “Skewness.” These and more modes could keep you busy during the longest winter evenings.

Notice in Figure 12 that I did not check Attempt to Automatically Align the Source Images. In the first example below (where I made a friend disappear), I captured the three images with the camera firmly mounted on a tripod; for a handheld shot that checkbox might be a good idea. For my Disparate Images stacking, since the images are wildly different anyway, there seems to be no benefit from trying to align them.

One of the things we commonly use Stack modes for is to remove any differences between images. This is easier to show than to describe, so take a look at Figure 13 below. I took three pictures of my friend and colleague, Dudley Harris. I had Dudley move to a different position in each of the three frames. I opened the three images (just JPEGs in this case) from Bridge and then executed the File > Scripts > Statistics > Median Mode. Like magic, CS4 Extended melded the three pictures together with no Dudley. That’s right—any image elements that were not common to all the images were eliminated. Now I don’t know how Dudley feels about this, but I think it’s pretty cool. You could use this technique to eliminate tourists from the Plaza Mayor in Madrid, for example.

Remember, you are not bracketing; you’re just shooting a series of equivalent exposures as people move through the scene. Merge them as described above and, presto, tourists are gone.

Note: Unlike combining images for HDR, when using Stacks mode, the images do not have to be the same size (though why you’d want them different is hard to imagine).

What we just did with Dudley was a typical use for CS4’s Extended Stack mode. But what if we use Stacks in a way for which it wasn’t intended? Sounds like fun, huh?

Figure 14 shows how I used the Scripts > Statistics > Median Mode to combine two completely different images. The final image has a quasi- Maxfield Parrish feel to it (Google as needed), with a fanciful range of tones and intertwined detail. The falls image was stacked with the trees image using Median mode.

Figure 11. Using CS4’s scripts and statistics.

Figure 12. Choosing the Median Stack mode.

Figure 13. Using CS4 Extended’s Stacks mode as intended.

Figure 14. Using CS4 Extended’s Stacks mode to combine images.

And in conclusion

If you’ve worked in Photoshop for more than 15 minutes, you know there are always several ways to get the same results. Your job isn’t to know all the ways; that pursuit can turn you into a pixel-pushing nerd who never gets behind the camera. Instead, be playful and childlike in your Photoshop explorations. I try to experiment with at least one new thing every time I sit down for an image-editing session. Sometimes the result is a fresh technique that I can use on my own images. And sometimes I glean current information about the program that will help my students as they tackle their own unique problems. The mere act of experimentation and exploration always helps you get more familiar with Photoshop. And since CS4 is the latest version of our digital darkroom world, the more familiar and comfortable you are, the more time and energy you’ll have for the creative aspects of shooting and image editing. Just think of Stacks and Disparate HDR as yet another job for that digital thighbone stirring the stew.

About the Author

Dan Burkholder
Dan Burkholder has been teaching digital imaging workshops for 15 years at venues including The School of the Art Institute, Chicago; The Royal Photographic Society, Madrid, Spain; The International Center of Photography, New York; Mesilla Digital Imaging Workshops, Mesilla, NM and many others. Dan’s latest book, The Color of Loss (University of Texas Press, 2008), documents the flooded interiors of post-Katrina New Orleans and is the first coffee table book done entirely using HDR methods. His award-winning book, Making Digital Negatives for Contact Printing, has become a standard resource in the fineart photography community. Dan’s iPhone images can be seen at: