In this tutorial please feel free to click on the thumbs to see larger images.
You may also download the before and after pictures of the Grand Canyon, however they are only for the use of this tutorial. Make sure you click on the thumbnail and then download the larger image.
Step 1 — Where are the Problems?
It separates the colour from the contrast — this makes it much easier to read the colours. The "L Channel" is the contrast of the image, it goes from black at 100, to white at 0. The "A Channel" goes from green to magenta, where green is a negative value and represents cool colour, and magenta is positive and represents warm colours. The "B Channel" goes from blue to yellow, where blue is negative and cool, and yellow is positive and warm. When both the A channel and the B channel are zero then it is greyscale. Refer to the picture below to see how to view the LAB colour read-out in your info palette.
Step 2 — Remove the Cast
Step 3 — Flatten
Once you are happy with your colour correction you need to flatten your image: cmnd/ctrl+e or menu-->layer-->merge
Step 4 — Channels
We are back to one layer.
Now we duplicate this layer cmnd/ctrl+j or drag your layer into the 'new layer' icon. While the new layer is selected, we will inspect the colour channels.
Do you see your colour channels? If not go to Window-->Channels
Step 5 — Channel Contrast
Here we are going to enhance the contrast of the picture by exploring each individual channel. Which channel is going to be our problem channel?
You guessed it... The BLUE channel.
Compare all channels by clicking on the R, B, or G layers in the channels palette and you will see that the blue channel will show the least contrast and the red channel will show the highest level of contrast. Therefore we will use the 'apply image' command to replace the blue channel with the red channel.
Make sure that the blue channel is selected. Image-->Apply Image
Refer to the image for the settings.
Let's click back on the RGB-channel and we see that everything is goofed up, it all looks funky pinky.
We select the 'Layer Blending Modes' drop down in the layers palette and select 'Luminosity' --> now everything looks beautiful again. This is because the luminosity blending mode only allows the contrast to change, and discards the colour of the layer.
flatten your image again: cmnd/ctrl+e or menu-->layer-->merge
Step 6 — More Contrast!!
Now lets boost the contrast in all of the individual channels.
Duplicate your layer once again. Inspect your channels and you may wish to also apply one of the layers on top of the others with the apply image command again. After, we will apply some curves directly to the individual channels. To do this simply select the channel you wish to operate on and press cmnd/ctrl+M to open the curves dialogue. Pay attention to the histogram in the back. In order to make more contrast we need to bring the curve in to be steeper where the majority of the action is on the histogram. It should be an "S" curve, which is considered a typical contrast curve. This may take some practice to get used to, but its worth it. The picture will probably look quite wacky once you return to the rgb channel, so switch to luminosity and ... voila. Now, press cmnd/ctrl+e or menu-->layer-->merge
Step 7 — Increase the contrast in the highlight areas
Duplicate your Background/Layer TWICE, then hide the top layer by clicking the little eye on the left of your 'Layers Palette'
Important: We talk about contrast. - Colour will not be effected here!
With the middle layer selected we are going to apply image again Menu-Bar-->Image-->Apply Image
This time we apply the RED channel. Check off 'INVERT' then hit okay
Change your layer blending mode to overlay.
Then go to -->Filter-->Blur-->Gausian Blur'
The setting for the gaussian blur will be determined by the picture, but it will usually be quite high. Remember we are only targeting the highlights. In the sample image you will see the benefits from this move in the the clouds mainly, but also in the rock formation on the left.
Next you will make the top layer visible again and change the blending mode to 'darken', this will allow the middle layer to only show through the highlights. On some images you may want to lower the opacity of the darken layer.
Step 8 — Merge visible
Now we will merge visible --> shift + cmnd/ctrl+e or menu, layer, merge visible
WOW. the picture is really starting to look great!!
Step 9 — Shadow Highlight Adjustment
Only do this if there are significant shadows and/or highlights, if it doesn't look good after or makes no different hit undo. Goto image-->adjustments-->shadow/highlight
The suggested settings are general settings that seem to work with most images and are known as 'rule of thumb'. You can save these as your defaults if you wish.
Step 10 — More Contrast?
Repeat step 5 to get some more clarity if you choose.
Step 11 — How's the colour now?
After all of that we should re-examine the colour and perform step 1 once more if necessary.
Congratualations! We have made it through a fairly intense colour and contrast workflow. This may seem quite lengthy now, but it actually quite a fast workflow, and should serve to develop your colour analysis significantly. For more on the LAB colour space and similar workflows, refer to the work of Dan Magulis.