Note: Photoshop CS4 used in this tutorial

There are times when we take an image of a beautifully lush and colorful scene only to see that the image captured by our camera's sensor doesn't quite reflect how we remember the scene. Rather than be disappointed with the image, there are some adjustments that we can make to get that image to be a truer representation of the original scene.

Here is an image taken in one of Oregon's lush forests shortly after a light rain and under overcast sky. I especially liked the scene due to the vibrant greens and reds of the trees and forest floor. Unfortunately, the colors in this image are no where near what I remember them to be.

The first step to making this image "come alive" is to add a Hue/Saturation layer and manipulate the saturation of the colors. Leaving "Edit" field set to "Master", moving the saturation slider to the right starts to give the image a better look. And for some images, this small adjustment may be enough. For this image, however, it still doesn't represent the lushness I remember, but its a start. We can move the slider even further right, but then the colors start to look a bit garish and unrealistic. We can also manipulate individual colors by selecting them from the "Edit" pulldown on the Hue/Saturation layer control panel and moving the saturation slider around to modify the intensity of the selected color. Be careful with the individual controls; things can get out of hand pretty quickly leading to some strange looking images. I left the saturation change here at 25% (on the Master level). The images below show the before and after results.

Now lets see what we can get using the LAB color space. The key feature of the Lab colorspace is that it contains every color that the human eye can see, making it very versatile for improving an image's saturation. Here are the components of the Lab colorspace:

1. L - Lightness channel; contains the tonality information for the image - does not contain any color information
2. a - a channel;contains the green-magenta color continuum
3. b - b channel;contains the blue-yellow color continuum

To get the most flexibility from this workflow approach, duplicate the current image (Image->Duplicate). We could work directly on the original image, but later on you will see why using a duplicate image gives much more flexibility. To covert the duplicate image to the Lab colorspace, use the Image->Model->Lab Color menu selection. Right away you should get an warning message. This gives one of the first limitations of this workflow. Moving in and out of the LAB colorspace can cause changes to the appearance of some Smart Objects, so they either need to be deleted or rasterized to avoid those problems. Rasterizing the layer will modify it so it is no longer a Smart Object. To do this, just click on the Rasterize button displayed on the message dialog.

Increasing the color saturation for an image in the LAB colorspace is very easy. Add a Curves layer to the image (Layers->AdjustmentLayer->Curves). In the Curves dialog, select the "a" channel from the Edit pulldown. Now select the black slider at the bottom of the histogram. This will display two boxes below the histogram: input and output. The diagram below shows the Curves dialog with the black slider selected.

Enter a value of '-75' in the Output field. This moves the black slider to the right causing the image to go a deep shade of green. Now select the white slider and enter '75' in its Output field. Thsi moves the white slider to the left adding more magenta to the image and balancing things out. It is important to use the same numeric values (negative in the black Output, positive in the white Output); otherwise the image will be given a color cast that will detract from its appearance. What this action is really performing is changing the color range of -75 to +75 to now be displayed as a new color range of -127 to +127. This steepens the curve of the green-magenta color continuum increasing the contrast between the colors. The colors might look a bit garish at this point but that will change when we take the next step. The number 75 that I chose works well for this image. For other images, you may want to use a different number to get the results that you are striving for.

Now repeat the same steps for the blue-yellow color continuum by selecting the 'b' channel on the Curves dialog and entering the same values of -75 and +75 in the black/white output fields respectively. This should bring the colors back into a better balance - though they may still look over saturated or even garish at this point. But this over-saturation in the Lab colorspace is what will provide more flexibility in RGB colorspace.

Now we move back to the RGB colorspace by choosing the Image->Mode->RGB Color from the Image menu. This gives us another warning. We cannot move out of the Lab colorspace with Layers; but we don't want to discard what we've done, so select the Merge button. This will flatten the image while retaining the adjustements that we made. The next step is to copy the Lab saturated image over to our original image (either by Select-All, Edit->Copy, Edit->Paste or by selecting the Move tool, holding the Shift button down and moving the Lab saturated image to the orignal image frame; the Shift key will ensure the images are properly aligned). We now have a new layer in the original image that contains the Lab saturated image. With this layer at 100%, it is the only part of the image that we now see and it is obviously over-saturated. The next step is to make some fine-tuning adjustments to this layer to get the best level of saturation.

Select the Lab saturated layer. Change the Blend mode and chose the "Color" blend mode. This mode passes along the hue and saturation information from the Lab layer but excludes any luminosity information. This will allow us to separately adjust the luminosity if so desired later. The next step is to decrease the opacity of the layer by draggin the opacity slider to the left. This is where the flexibility of doing the Lab adjustments on a separate image are highlighted. We can now adjust the opacity slider to modify the saturation of the image. And, after other changes that we might make to the image, we can come back and readjust the saturation merely by adjusting the opacity of this layer. The difference between the original image, using just a saturation layer and using the Lab saturation technique is clearly evident when the images are compared side by side.

The Lab workflow has one other limitation. It works best with images that are in a large colorspace such as ProPhoto RGB. If the original image is in a small colorspace (i.e. sRGB), you could end up with colors in the Lab image that do not exist in the original colorspace. These colors would be out of gamut in the original colorspace and would be rendered back itno that colorspace when the image is converted back from Lab resulting in some degradation. It is always advisable to work in the largest colorspace you have available.

Hope this technique can help you give your images the look that you remember from when they were taken.