Making Your Image Pop Using LAB Curves
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Making Your Image Pop Using LAB Curves
Tutorial by Rutt
Introduction: This tutorial explains a recipe that can make almost any picture more dramatic and appealing. It uses some very advanced techniques in simplified, stylized ways. Because of this, anyone with Photoshop version 5 or later has the tools to use this technique.
The tutorial is in two parts. I will walk you through the recipe, showing it's application to a particular image. Then I will explain why it works. You don't actually need to know why this works in order to use it, but that understanding can lead you to more advanced techniques and a much more sophisticated understanding of the color and how to manipulate it in your images.
No Pop: Here is the starting point. I took this picture on a rainy October afternoon in Vermont. There's a lot about it I do like, but it's pretty drab, not really worth a second look the way it is. I remember the colors quite differently. In my memory the greens were very deep, like the emerald greens of Ireland. The barn was red, not brown. The sky was much more interesting and varied between low clouds and bluer areas. In fact, everywhere I looked, I saw more color variation, more contrast and more detail. That's the pop I wish this picture had.
Quick Start: For those who are already somewhat familiar with Photoshop, here is the basic recipe. I'll walk though the steps in some detail below, so if you need more help, just skim this list of steps and then use it as a guide to the detailed explanation below.
Convert to the LAB color space
Curves
Steepen A and B channels symetrically by bringing in the endpoints of each curve toward the center equally. After this, the curve (line actually) will still cross the center horizontal center at the vertical center. Start out by experimenting with bringing in each end point between 10% and 20%.
Establish light and dark points by moving the endpoints of the L curve inwhard. Optionally, steepen the L curve through the areas where the detail is of most interest.
Activate only the L channel
USM, trying the values 200, 1.0, 10
Details: If any or all of that went over your head, don't panic! I'm going to go over it in excrutiating detail. Follow along and you'll easily be able to apply this recipe to your own images.
What's going on here?
You can stop right now if all you want to know is how to add pop and aren't interested in being able to do even a lot better. But, For me the interesting part of this chapter is the theory behind it. Granted the technique is a super simple way of improving tons of shots, but understanding why it works opens the door to a greater understanding of how to use (and not misuse) LAB color corrections and of digital color correction in general. Human sight is a marvelously complex and highly evolved system. It self calibrates to emphasize differences in color and in shade. When we are in the middle of the forest surrounded by infinite subtle shades of green, our vision pulls these shades apart allowing us to see enormous variation. On the beach in the late afternoon, we can discern traces of the impending sunset and see the complexity of hue in the sand and sky. But the camera doesn't do this. It doesn't "know" when to do it. When we look at a picture, our vision does not self calibrate because the picture only occupies a small portion of our field of view and is surrounded by all kinds of competing cues. So the picture won't capture the same intensity and variety of color we saw when we took it. Even if it is a faithful rendering of the "true" colors of the scene, it does not capture what we saw.
The basic LAB enhancement can restore the picture so that it captures the vision of our memory. Steepening the A and B curves moves colors apart from each other. This kind of symmetrical curve steepening applies a constant multiplier to the colors. If it was X amount of green before, it will be X*N green after and similarly for magenta, blue, and yellow. The green gets greener in proportion to how green it was to begin with. The difference between blue and yellow is magnified as slight variations from neutral are pushed away from neutral toward in the direction of their tint. So the sky of my shot becomes more of a tapestry of different shades of blue. The grass and hills in the background all show greater color variation. Similarly for the other elements of this picture. It's mush more as I remember it.
Steepening the L curve over the areas of interest in the image similarly apes the way our vision works. The steeper the curve, the greater the detail, as Dan likes to say. I found no interesting detail darker than the shadows in the barn. So I pulled the right end of the L curve in almost to that point. I found no interesting detail lighter than that cloud, so I pulled the left end of the L curve in almost to that point. Then I made it a little steeper though the elements of the picture I really wanted the viewer to see.
Acknowledgments
This tutorial is pure Dan Margulis. The technique described here is taken from Chapter 1 of his book Photoshop LAB Color : The Canyon Conundrum and Other Adventures in the Most Powerful Color Space. Dan is the living grandmaster of digital color correction and enhancement. He has approached the topic as both a scientist and artist, has constantly innovated, and has written on the topic with enormous and increasing lucidity. Anyone who want to get good at photoshop to make both color and black and white images look better and more realistic can peruse no better path than to read his books and try to master some of his ideas and techniques. Unfortunately this can't be seen as a short or even a finite process. Dan challenges his readers to really understand color both in theory as well as in practice. The reward is true understanding, independent of any recipe which can be applied though a variety of tools as appropriate. Plus I find Dan's writing a gas to read. He writes well and has a wonderful dry sense of humor which makes the inevitable second reading a pleasure.
This tutorial started it's life as a summary of chapter 1 of Dan's LAB book. It was originally written as a part of a reading book organized as a forum for discussion and understanding of that book. That forum is very much still alive and much more information is available there.
Ask questions about this tutorial in this thread on Digital Grin!
Tutorial by Rutt
Introduction: This tutorial explains a recipe that can make almost any picture more dramatic and appealing. It uses some very advanced techniques in simplified, stylized ways. Because of this, anyone with Photoshop version 5 or later has the tools to use this technique.
The tutorial is in two parts. I will walk you through the recipe, showing it's application to a particular image. Then I will explain why it works. You don't actually need to know why this works in order to use it, but that understanding can lead you to more advanced techniques and a much more sophisticated understanding of the color and how to manipulate it in your images.
No Pop: Here is the starting point. I took this picture on a rainy October afternoon in Vermont. There's a lot about it I do like, but it's pretty drab, not really worth a second look the way it is. I remember the colors quite differently. In my memory the greens were very deep, like the emerald greens of Ireland. The barn was red, not brown. The sky was much more interesting and varied between low clouds and bluer areas. In fact, everywhere I looked, I saw more color variation, more contrast and more detail. That's the pop I wish this picture had.
Quick Start: For those who are already somewhat familiar with Photoshop, here is the basic recipe. I'll walk though the steps in some detail below, so if you need more help, just skim this list of steps and then use it as a guide to the detailed explanation below.
Convert to the LAB color space
Curves
Steepen A and B channels symetrically by bringing in the endpoints of each curve toward the center equally. After this, the curve (line actually) will still cross the center horizontal center at the vertical center. Start out by experimenting with bringing in each end point between 10% and 20%.
Establish light and dark points by moving the endpoints of the L curve inwhard. Optionally, steepen the L curve through the areas where the detail is of most interest.
Activate only the L channel
USM, trying the values 200, 1.0, 10
Details: If any or all of that went over your head, don't panic! I'm going to go over it in excrutiating detail. Follow along and you'll easily be able to apply this recipe to your own images.
- 1. Convert to LAB: The figure shows how to do this. Click on the Image menu, then the Mode submenu, and finally on the Lab Color item.
- 2. Open the Curves dialog: The figure shows how. Click on the Image menu, then the Adjustments submenu, and finally on the Curves item. The key sequences to the right of the menu show shortcuts which you can use instead of the mouse. In this case Command-M on a Mac or Alt-M on windows would also bring up the curves dialog.
- 3. Steepen the A and B curves: The curves dialog allows you to alter your image in each channel of it's current color space. In this case, the image has been converted to LAB and has three channels, Lightness, A, and B. You can change which of these the curve applies to by clicking on the Channel dropdown and selecting an item. For now I am going to work with the A and the B curves.
Exactly what I am going to do with these curves is to make them steeper by dragging each endpoint toward horizontally toward the center while keeping it at the bottom or the top of the graph.
It's important that I have steepend the curves symetrically and equally.
The steepening is symetrical in that the two endpoints of each curve have been moved inward by exaclty the same amount, in this case 15%. The center of the line still crosses the midpoint of the graph. For now, treat this as a matter of revealed truth, the 11th commandment.
The steepening is equal in that I have done exactly the same thing to both A and B curves.
At this point the image starts to come alive. There is a lot more variation in the colors. The barn is looking redder. The individual leaves of grass and the vegetation in the trees is more differentiated.
You should experiment with just how much steepening you use in this step. Initially, try values between 10% and 20%. Eventually, you'll be able to estimate good values just by looking at the original.
How to work with curves: So far, so good, but the next step requires a little more dexterity with the curves dialog, so I'm going to take you on a little detour and explore a few of its features.
Curves Preview: The figure shows the mouse over the Preview check box. Clicking this off and on shows the image before and after the curve is applied. Get used to using this a lot. It's the best way to see where you are going and to make mid course corrections.
Getting lightness on the left and darkness on the right
This step isn't strictly necessary, but it's easy and avoids confusion. The curves dialog has two possible orientations. The bottom right can either be the lightest or darkest possible point along both dimensions. It has become customary to write about these curves with the orientation as shown. If it is the opposite, click on the double arrow in the center of the horizontal axis legend (as shown) to reverse it.
Using the Curves Dialog to measure points in your image:
This feature is the great secret of being able to use curves well. With the curves dialog open, click the mouse on any spot of your image and a point will appear on the dialog showing the value of the color at the spot on the curve. Drag the mouse cursor (move it with the mouse button (right mouse if you have more than one mouse button) held down, and the point will move along the curve to show the value dynamically. I am about to make very good use of this feature in order to implement the next step of the recipe.
- 4. Establish light and dark points
Generally, images look best when they use the full range of available contrast. That means that they have a darkest spot which is truly black and a lightest spot which is truly white. It's actually quite a bit more complicated than that, but it's easiest to understand by doing than by theorizing. I used the Channel drop down to switch to the Lightness channel of the curves dialog. Then I used the mouse to look around for the lightest point I could find in the image. It's in the clouds. You can see that it's about 5% above the 0,0 point of the graph, meaning that it isn't as light as it could be.
Similarly, I used the curve and mouse trick feature to find the darkest part of the picture. There are lots of candidates, inside the barn. But none of them measures 100 on the graph, meaning they are all a little gray instead of black.
In the course of my mouse and curve explorations, I found no point of the image lighter than about 5% and no point darker than about 93%, so I decided to move the endpoints by those 5% and 7% respectively so that the lightest point of the image would lie very bottom of the curve, where it would really be completely light and the darkest point would be at the very top where it would really be completely dark. I've shown the curve.
Here is what I got just by the simplest versions of steps 3 and 4.
Compare to the original for pop! The deep shadows inside the barn are really dark. The sky is much lighter. Because the image now uses all of the available contrast, much more detail is visible nearly everywhere in the image. And it has lost that horrible drabness.
Optionally, make the curve steeper though the areas of greatest interest:
Skip this step if you like. You can always come back and experiment later on. But the idea is to make the most important areas of the image look better and stand out by stealing contrast from less important areas. In this case, there isn't any detail I really care bout in the deep shadows, so I'd rather have more contrast in the sky, grass, old truck, and outside of the barn. So I grabbed the curve just before it's darkest part and pulled it up a bit to make the curve steeper below it (where all that good stuff lives) and a little shallower inside the barn (where there really isn't anything interesting.)
The difference between this version and the one without the L curve midpoint is more subtle than the difference I got just by establishing white and dark points. But it's substantial. See how much better the clouds stand out in the sky. Most importantly see how the texture of the barn planks and grass has improved.
Done with Curves, whew!
At this point I've used LAB curves to add lots of pop to my picture. So I just clicked OK in the dialog box and applied the curves to image and was ready to move on.
If you've come this far, you've done something lots of people regard as the deepest of Photoshop black magic, used LAB curves to enhance your image. There are lots of well respected digital photographers, even on dgrin, who have never come this far. Give yourself a pat on the back. And it wasn't really that hard, was it? - 5. Activate the L channel
The last thing I want to do is sharpen this picture. Sharpening is a whole topic in itself and there is a separate tutorial on the topic. But since it can make a dramatic difference in the quality of a majority of digital images, I'll show how to do a quick and dirty job that should look pretty good on most images. But if you can, I strongly encourage you to read my sharpening tutorial.
In preparation for sharpening, I activated the L channel. I did this by finding in in the Channels palette and clicking it it. See how it turns blue and the other channels are white and the eyeballs are gone from the boxes to their left.
When the eyeballs next to the other channels disappeared, the color channels became invisible, with the result that the image now displays in black and white, probably not what I wanted. It's easy to fix this, though. Click on the empty box to the left of the top line, the composite Lab channel, and the eyeballs for all the channels will return and the colors will again be visible.
- 6. Sharpen with the Unsharp Mask Filter
Bring up the Unsharp Mask dialog by clicking first on the Filter menu, then on the Sharpen sub menu and finally on the Unsharp Mask item.
Set the values as shown here: Amount = 200, Radius = 1, Threshold = 10.
Voila
What's going on here?
You can stop right now if all you want to know is how to add pop and aren't interested in being able to do even a lot better. But, For me the interesting part of this chapter is the theory behind it. Granted the technique is a super simple way of improving tons of shots, but understanding why it works opens the door to a greater understanding of how to use (and not misuse) LAB color corrections and of digital color correction in general. Human sight is a marvelously complex and highly evolved system. It self calibrates to emphasize differences in color and in shade. When we are in the middle of the forest surrounded by infinite subtle shades of green, our vision pulls these shades apart allowing us to see enormous variation. On the beach in the late afternoon, we can discern traces of the impending sunset and see the complexity of hue in the sand and sky. But the camera doesn't do this. It doesn't "know" when to do it. When we look at a picture, our vision does not self calibrate because the picture only occupies a small portion of our field of view and is surrounded by all kinds of competing cues. So the picture won't capture the same intensity and variety of color we saw when we took it. Even if it is a faithful rendering of the "true" colors of the scene, it does not capture what we saw.
The basic LAB enhancement can restore the picture so that it captures the vision of our memory. Steepening the A and B curves moves colors apart from each other. This kind of symmetrical curve steepening applies a constant multiplier to the colors. If it was X amount of green before, it will be X*N green after and similarly for magenta, blue, and yellow. The green gets greener in proportion to how green it was to begin with. The difference between blue and yellow is magnified as slight variations from neutral are pushed away from neutral toward in the direction of their tint. So the sky of my shot becomes more of a tapestry of different shades of blue. The grass and hills in the background all show greater color variation. Similarly for the other elements of this picture. It's mush more as I remember it.
Steepening the L curve over the areas of interest in the image similarly apes the way our vision works. The steeper the curve, the greater the detail, as Dan likes to say. I found no interesting detail darker than the shadows in the barn. So I pulled the right end of the L curve in almost to that point. I found no interesting detail lighter than that cloud, so I pulled the left end of the L curve in almost to that point. Then I made it a little steeper though the elements of the picture I really wanted the viewer to see.
Acknowledgments
This tutorial is pure Dan Margulis. The technique described here is taken from Chapter 1 of his book Photoshop LAB Color : The Canyon Conundrum and Other Adventures in the Most Powerful Color Space. Dan is the living grandmaster of digital color correction and enhancement. He has approached the topic as both a scientist and artist, has constantly innovated, and has written on the topic with enormous and increasing lucidity. Anyone who want to get good at photoshop to make both color and black and white images look better and more realistic can peruse no better path than to read his books and try to master some of his ideas and techniques. Unfortunately this can't be seen as a short or even a finite process. Dan challenges his readers to really understand color both in theory as well as in practice. The reward is true understanding, independent of any recipe which can be applied though a variety of tools as appropriate. Plus I find Dan's writing a gas to read. He writes well and has a wonderful dry sense of humor which makes the inevitable second reading a pleasure.
This tutorial started it's life as a summary of chapter 1 of Dan's LAB book. It was originally written as a part of a reading book organized as a forum for discussion and understanding of that book. That forum is very much still alive and much more information is available there.
Ask questions about this tutorial in this thread on Digital Grin!
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