Inverting Backgrounds with LAB
Intro | Multi-RAW Processing | Creating HDR Images by Hand [Part I] | Creating HDR Images by Hand [Part II] | Sharpening in LAB Color | Converting to Black and White | Using LAB Color Adjustments | Inverting Backgrounds with LAB | Intro to Compositing | HDR in Adobe Photoshop CS5 | Using Image Apply Image | Aging Photos Roundup | Making Colors Pop in Photoshop
Intro Image: This spectacular effect of transparent flower petals on a black background was achieved using an LAB inversion.
In two previous columns I’ve shown you some of the uses of the LAB color space in the Photoshop darkroom. In Sharpening in LAB Color I showed you how to use LAB for attractive, compositional sharpening. Using LAB Color Adjustments explained how to make creative use of LAB color effects by combining layers and blending modes in LAB.
This column takes a detailed look at another helpful LAB technique that I frequently use in my work: inverting the background.
Most often, this means converting a black background to white, or a white background to black. There are at least four possible reasons you might want to do so:
- There were technical reasons why you had to shoot against a specific background
- You had no choice about the background when you shot the image
- You want to invert the background for creative effect
- You’d like to present a matched pair of photos of the same subject, one on a white and the other on a black background
In this column I’ll explain the basics of inverting a solid black or solid white background in LAB. Next, I’ll examine each of the possible scenarios for creating a final image using LAB background inversion techniques—so that when you are in a situation in which this technique applies you’ll be able to recognize it. Along the way, I’ll suggest creative alternatives for you to play with.
In my previous columns Sharpening in LAB Color and Using LAB Color Adjustments I explained how LAB works in Photoshop in the context of what you need to know to be able to work in this “most powerful” color space. You might want to refer back to these articles to review the conceptual basics of LAB, for an overview of LAB basics, and for color manipulation techniques. In Using LAB Color Adjustments I cover some of the same ground as this article with regard to LAB inversions—but the emphasis is focused on the general topic of creative color adjustments, not the specific and useful technique of creating a realistic background shift.
Background inversion using LAB is a technique I often use in my own work, and it can look great. I can’t wait to share this idea with you!
Converting to LAB Color
It’s easy to convert an RGB or CMYK image to the LAB color space. There are a few advanced wrinkles in the process, and if you are interested in the subtleties you should check out my Using LAB Color Adjustments column.
LAB has been called the “most powerful” color space. Using LAB Color Adjustments provides some useful information about what LAB is, how it compares to the RGB and CMYK color spaces, how you should think of color spaces and LAB generally, and how to integrate LAB techniques into your Photoshop workflow.
I’m not of a mind to repeat the material from the previous column, but I do want to provide sufficient information for you to get started inverting your backgrounds without having to refer back.
To head into the LAB color space, you can convert to LAB simply by choosing Image > Mode > LAB Color from the Photoshop menu.
Inversion in RGB
In Photoshop, an inversion means to reverse the values in a channel or channels. For example, the possible range in values in the R channel of an RGB image is from 0 to 255. Following an inversion, a 0 value would become 255, and a value of 255 would become 0. The concept is pretty intuitive, but in case you are interested, the formula for determining intermediate values (such as 80) following an inversion is to find the absolute value of the channel value minus the maximum channel value.
Consider an RGB point with a value of R=80, G=74, and B=117. Which, by the way, is a pale lilac or magenta. If you invert the R channel, you get the absolute value of 80 — 255, which equals 175. The RGB color value (175, 74, 117) translates to a somewhat rosier magenta than the original color. You can see the transformation by comparing the new color to the current color shown in the swatch in the Color Picker window shown in Figure 2.
The bottom line is the RGB (or CMYK) channel inversions usually don’t have that much impact and/or they lead to muddy looking overall colors.
Figure 2: The Color Picker shows you before and after values visually; you can use this to check the visual impact of an inversion.
Fortunately, you don’t have to do the math to understand the impact of an inversion in Photoshop. It’s easy to apply an inversion to a channel and visually see the results. I’ll show you the simple steps to take in a moment.
It’s Better in LAB
LAB inversions beat RGB (or CMYK) inversions hands down for impact, intuitiveness, and just plain coolness. This primarily has to do with two aspects of LAB color structure. See Using LAB Color Adjustments for some more of the details, but they boil down to two things:
- Black and white information, sometimes called luminance information—and designated by the Lightness or L channel in Photoshop—is separated from color information in the A and B channels. This means that it is possible to invert a black background and turn it white—or a white background and turn it black.
- The “color antagonist” structure of the LAB channels means that you get dramatically opposed colors when you invert in LAB, not just variations (as in RGB or CMYK).
The short version is that you get bigger moves in LAB by inverting than in other color spaces, and the moves are more predictable. For example, to create the image shown at the beginning of this article (Figure 1), I photographed flowers for transparency on a light box as shown below (Figure 3). To create the dramatic image shown in Figure 1—which has been a steady source of licensing income for me, by the way—I inverted the L channel in the original image.
Figure 3: Photographing flowers for transparency on an illuminated white background is a technique I often use—with L channel conversion in the back of my mind.
Inverting the L Channel
Take the delicate photo of the model Bonnie carrying an umbrella shown in Figure 4. I photographed Bonnie on a completely white background, and slightly overexposed for a high-key effect.
Figure 4: The starkness of the white background in this photo made me wonder what would happen in an inversion.
To invert the background of the photo, I first converted to LAB color as explained earlier in this column. Next, in the Channels Palette, I made sure the Lightness channel was selected and all the channels were visible as shown in Figure 5. The blue band you see in Figure 5 indicates the Lightness channel is selected; the “eyeball” icon in the left-hand column means that a channel (in this case, all three channels) are visible.
Figure 5: The Lightness channel is selected, but all three channels are visible.
With the Lightness channel selected, to apply an inversion, choose Image > Adjustments > Invert from the Photoshop menu.
The results, shown in Figure 6, are interesting and dramatically different from the starting place—with very minimal effort.
Figure 6: The white background is now black; note that the black shoes are now white.
By the way, if I’d wanted a more realistic version of the model on the black background, it is fairly easy to layer the original photo back on top of the new version, masking out the background areas. This would give you a more realistically rendered figure on a black background.
The Background Is What It Is
Portrait photographers know that backgrounds in their photos can be crucial. It’s sometimes possible to “fix” a problematic background when shooting—for example using a cloth or other prop.
But if you’ve already taken the photo, and the background isn’t that great, then you’re stuck, right? The background is what it is.
Not so fast, pardner. Obviously, with digital, it is possible to composite in a new background, although you have to take into consideration how easy—or hard—it is to get a clean mask of the subject you want to cut out and place in front of a new background. My next column in this series introduces the art and craft of photo compositing.
A channel inversion is both more exotic and less effort than compositing-in a new background.
In the previous section, I showed you how to invert the L channel to “trade” a black background for white—or one that is white for black. By the way, how much this adjustment will change the foreground subjects of your image depends upon their luminance information.
You are not limited to these possibilities. There are a great many permutations and variations possible in LAB color.
So no, the background is not necessarily determined—until you are finished with your LAB color moves in Photoshop.
Three-Channel LAB inversion
Straight L-Channel inversion creates the most basic color swaps and black-for-white (or white-for-black) backgrounds. This is the best starting place for building nearly realistic effects.
But if you are more interested in wild and whacky color effects on a black background, it’s worth giving three-channel LAB inversion a try.
Start by selected all three channels in the Channels Palette as shown in Figure 7.
Figure 7: All three channels are selected in the Channels Palette.
Once again, apply an inversion by choosing Image > Adjustments > Invert from the Photoshop menu.
The results, shown in Figure 8, are striking, and arguably every bit as useful as the L-Channel inversion.
Figure 8: The three-channel inversion turns the background black and the model blue.
Don’t Forget Equalization for Your Background
The primary thrust of Using LAB Color Adjustments was to show you how to use LAB color equalization to add fancy color effects. But don’t dismiss equalization. It can also be an effective and easy way to generate interesting backgrounds. The Equalize adjustment is more than just a pretty face, and sometimes can give you dynamic backgrounds as easily as choosing the adjustment.
For example, equalizing the A channel turns out to create a very interesting halo effect around Bonnie’s umbrella (see Figure 10).
To set this up, in the Channels palette, I chose the A channel. I made sure all three channels were visible as shown in Figure 9. Finally, I chose Image > Adjustments > Equalize.
Figure 9: The channel I want to equalize is selected.
The results of this simple equalization are quite striking, as you can see in Figure 10.
Figure 10: Equalizing the A Channel creates a turquoise background and a halo effect around the umbrella.
By the way, the white halo effect after the equalization is pretty nifty, right? I didn’t do anything special to generate it—it’s an equalizing color shift of spectrum values that weren’t apparent before the adjustment.
Shooting for Inversion
Shooting with LAB background inversions in mind primarily means working with white or black backgrounds. There’s nothing to stop you from turning a red background green (using an A channel inversion) or a blue background yellow (using a B channel inversion), but usually these don’t work cleanly on the photo’s primary subject. Black or white backgrounds are simply more useful.
Transparency or translucency combined with a white background is an almost sure sign that a LAB background inversion will create an interesting effect. To “encourage” the transparency required with a white background I moisten subjects were appropriate, shine light through the subject, use high-key exposures, and use an overall consistent light (or some combination of these techniques).
The cherry blossoms shown in Figure 11 were shot on an illuminated 5200 degrees Kelvin white light box using all these techniques.
Figure 11: These cherry blossoms were photographed for transparency with inversion in mind.
I liked my initial version of these cherry blossoms after processing them in Photoshop, but I found myself much more excited by the alternate cherry universe created after a series of LAB background inversions, and shown in Figure 12.
Figure 12: The alternate cherry universe was created using a series of LAB background conversions.
LAB background conversions can be used successfully on many kinds of photos. It’s a simple kind of “move”; and it’s easy to see the impact of your processing. Don’t hesitate to try applying multiple background inversions to a single image (to achieve effects such as that shown in Figure 12).
You also can experiment with applying LAB inversions to unlikely subjects for ethereal and otherworldly effects.
For example, the studio shot of the model Christianna shown in Figure 13 isn’t that unusual for the genre.
Figure 13: This fairly typical studio shot of a model is pleasing but nothing one hasn’t seen before.
Following a simple L-Channel LAB inversion, the portrait of Christianna becomes exciting, unusual and ghostly.
Figure 14: An L-Channel inversion turns this model into something like a ghost,
You can learn more about the in-depth specifics of working with LAB color in my book The Photoshop Darkroom: Creative Digital Post-Processing (Focal Press, 2010) and my new book that is currently in the works The Photoshop Darkroom 2: Creative Digital Transformations (to be published by Focal Press in 2011). This article explained:
- Converting to LAB
- Inversion in RGB
- Why LAB inversion is better
- Inverting the L Channel
- Three-channel LAB inversion
- Shooting for inversion
Other Photoshop Tutorials
Creativity in the Photoshop Darkroom by Harold Davis: Multi-RAW Processing | Creating HDR Images by Hand [Part I] | Creating HDR Images by Hand [Part II] | Sharpening in LAB Color | Converting to Black and White | Using LAB Color Adjustments
Harold is the author of The Photoshop Darkroom: Creative Digital Post-Processing (Focal), Creative Composition: Digital Photography Tips & Techniques (Wiley), Creative Night: Digital Photography Tips & Techniques (Wiley), Creative Close-Ups: Digital Photography Tips & Techniques (Wiley), Practical Artistry: Light & Exposure for Digital Photographers (O’Reilly Digital Media) and other books. Harold gives frequent digital photography workshops, many under the auspices of the Point Reyes National Seashore Association.
Text and photos ©2010 Harold Davis.
Text and photos ©2010 Harold Davis.