Photoshop CS3 Lab Color Enhancement: Central Park Wysteria

Here’s another example of an image quickly improved by enhancements and sharpening in the Lab color space. This shot was taken in Central Park of a wysteria vine that had taken on tree-like proportions. All I had with me was a small point-and-shoot and we were in a bit of a hurry, so I just snapped the picture letting the camera do everything. In just a couple of minutes playing/working in Lab Color made a substantial difference. The result is an image that has much stronger colors and makes me happier to look at. Here’s a swatch of the original image:

I started by converting the image into Lab (Image -> Mode -> Lab Color). From here I created a new curves adjustment layer (Layer -> New Adjustment Layer -> Curves…). I usually start by adjusting the ‘b’ channel first. This allows me to white balance the image as the ‘b’ channel is responsible for the blue to yellow range of colors. A negative ‘b’ means a blueish cast.

If you have the Info window open (Window -> Info) you can see the L, a, and b values of the point under your cursor. As you mouse over an image, if there are areas that you know should be colorless (white, grey, or black) you can check the ‘b’ values. If there is a consistent negative ‘b’ value in these areas, you can use the ‘b’ channel curves adjustment to remove it. Shifting this curve to the left (as I have my curves setup) will remove the blue cast. Here is the ‘b’ channel curve that I used:

In the case of this image, I didn’t feel that there was any white balancing necessary, so I simply steepened the ‘b’ curve by brining the end points in the same amount (+/-99). A similar curve in the ‘a’ channel results in a good starting correction curve pair for working in Lab. I have a few variations of these curves saved as presets which make them easier to use. To save a preset, click the small box between the Preset pulldown menu and the OK button in the Curves window, select Save Preset… and give your preset a name. I use ‘Lab simple ab95′ as the name of curves that pull the endpoints of both ‘a’ and ‘b’ channels to +/-95, for example. Here’s the ‘a’ curve for this correction:

These two adjustments result in this:

At this point the colors are more vibrant and the image is starting to look better. There’s still more that we can do to help it, though. A little bit of contrast helps many images, so this is the ‘L’ channel curve I used:

Resulting in a slightly more contrasty image with a little more separation between the shadows under the limbs and in the leaves:

At this point, I usually flatten the image and do some sharpening and call it a day, but I felt like I could do more with this image. In particular, I though the colors of the blossoms could be bluer. In RGB, this could be done, but at the expense of causing everything to take on a blue tint. In Lab, it’s very simple to make an adjustment that affects one part of an image that is at an extreme of one of the a/b channels. In this case, the ‘b’ channel is much darker in the blossom area than anywhere else. We can use this in a mask to affect changes selectively.

I clicked on the layer mask icon (starts out as a white rectangle between the curves icon and the text ‘Curves 1′ in the list of layers) to highlight it (it gets little corners outside the rectangle when it is selected. I clicked Image -> Apply Image… to bring up this dialog box:

I set the Layer from which to apply to Background and set the Channel to ‘b’ so that the ‘b’ channel of the original image (before any color correction) is used as the mask. I also set the blending mode to Multiply from Normal which has a dramatic effect on the image. When these steps are done, the resulting layers display looks like this:

Note the changes in the layer mask from a white rectangle to the varied grey version. I lowered the opacity to 60% to see the effect, but ultimately raised it to 90%. While I made this move to improve the blue flowers, the multiply blending strengthened the green leaf colors and darkening the image overall. However, comparing the blossoms before and after, they retain much of their brightness while adding some blue tint. This wasn’t exactly where I was heading, but I liked it when I got there. Here’s where we are now:

Whenever using a layer mask in this manner, it is best to blur the mask. It seems wrong, but the results are always so right. With the layer mask still selected, click Filter -> Blur -> Gaussian Blur… to get to this dialog:

A blur of 20 pixels is a reasonable choice most of the time, although it’s really only necessary to blur to the point at which the details in the mask layer are lost and only soft shapes remain. After applying the gaussian blur to the layer mask, we get:

From this point, I flattened the image. If you are in Lab Color, it is definitely best to do any sharpening before leaving the Lab. Switching over to the Lightness (L) channel before sharpening means that only this channel will be affected. Since the L channel contains the detail of the image, it is the optimal place to sharpen without risking color aberrations (which are really evident when sharpening in RGB without applying it to the image luminance). Pressing CMD-1 on a Mac (or some equivalent on a PC.. ALT?) will show the L channel (it looks like a black and white version of the image):

Using our old friend Unsharp Mask (Filter -> Sharpen -> Unsharp Mask…) with these conservative values:

results in the following sharpened image:

Putting it all together, we went from this (click through to see a bigger version at flickr):

Central Park wysteria - original before Lab color enhancement

to this:

Central Park wysteria - after Lab color enhancement

  • Dale

    Is “Lab Color Space” a program? I’m guessing it is a feature of a specific program that I am supposed to recognise from the illustrations. What program?

    And then change the title to “Example of using LAB Color Spaces in program XXXXX to improve a picture of wisteria” or something equally helpful to those who don’t already know what you are talking about.

    Thanks

  • David

    I second Dale’s comment. ^
    I’m very interested in this article, but it looks like it’s just pulled from the middle of a book or website without any clue as to what program it’s using or referring to.
    The frustration is it’s potentially very useful, but without the missing info, useless.

  • David

    OK,
    I’ve done some Google research based on the info in this article and it really is useful – if you have Photoshop.
    I have Elements, and the Color Lab Mode is not available in that program.
    It would be nice to know which other programs, (if any), support Color Lab Mode.

  • qmchenry

    Hey guys, thanks for the feedback. Yes, I did perform these color manipulations using Photoshop CS3, although my recollection is that they will work as is in CS2 as well, although I can’t speak to earlier versions. Great point about leaving out that crucial information. This is my second post about the Lab color space and I am still trying to determine what interest level there is in this very powerful manipulation technique.

    As I have time, I intend to determine what other applications can make Lab color moves and describe those as well. I was hoping that the Gimp had a plugin that would work, but I get conflicting Google results for that and haven’t had any luck finding one. It’s good to know (although unfortunate) that Photoshop Elements doesn’t support the Lab color space. For a little more introduction into Lab color, read the first few paragraphs of my first post, Lab experiments: Basic Lab color space enhancement in Photoshop CS3. I’ve also retitled the post to reflect the application used. Honestly, I was really more concerned with presenting the workflow (which I’m still not really happy with) and missed the boat on providing additional background. If anyone has any suggestions about presenting this type of info, please share — would a clear video of the screen with verbal descriptions be useful?

  • Rob

    Woooahhh.. that’s . . . a lot of saturation.

  • qmchenry

    Rob, yeah, it’s quite a difference between the two. I’m inferring you think it’s too much, and that’s okay. Color correction/enhancement is a subjective process that not only depends on the eyes looking at it, but the specifics of the display device used (different gamma values of operating systems, massively different monitor settings and characteristics, etc), and the ultimate use of the image, press or web. On my system, I felt the moves looked good, but, unfortunately, placing an image on the web is a crap shoot for color.

    Did I go too far with this image? Maybe.. the multiply blending mode is powerful stuff. If you were processing this, you could easily tame down the enhancements with a lower opacity. The cool thing about Lab, and the message I’m trying to convey, is that it makes things possible that traditional RGB moves simply cannot do. For example, if we look at what RGB saturation changes can do, we get this:

    This image shows the same chunk as processed in the post above. On the left third is the original image. The middle third has a saturation shift of +30 in RGB mode, the right third goes to +60 saturation still in RGB. While there are things we could do to repair some of the damage done to the image with these moves, and while there is arguably some improvement to the colors of the image, the main point is that changes in RGB inevitably causes changes not only to color but also to luminosity. In the +30 saturation move, the blossoms are significantly brighter and in the +60 case the leaves become radioactive. One of the principle advantages to working in Lab is that the color (ab) is separate from the brightness/detail (L). Combined with the speed and consistency of Lab corrections, it’s hard to beat.

  • tlawski

    I’ve been searching or the longest time for a site that would help with this feature in CS3. I’m a relative noob when it comes to photoediting and this one the one thing that I really wanted to learn.

    I’ll most definitely have to Ctrl-D this one!

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