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Finessing the Lightness channel with Curves

From: Photoshop CS3 Mastering Lab Color

Video: Finessing the Lightness channel with Curves

So far we have done a good job of correcting the colors in this image in the Lab Color mode, but our goal is not to do a good job, it's to do a great job. So this is Lab version of the image thus far and the name of this document by the way I have gone ahead and saved my progress. It's called The Lab clouds so far.psd found inside the 02 what it can do folder. These are the RGB clouds, which look somewhat better in the color department a little bit I would say but look much worse in terms of the noise department, witness most prominently up here in the upper right corner of the image and this is what we are going for.

Finessing the Lightness channel with Curves

So far we have done a good job of correcting the colors in this image in the Lab Color mode, but our goal is not to do a good job, it's to do a great job. So this is Lab version of the image thus far and the name of this document by the way I have gone ahead and saved my progress. It's called The Lab clouds so far.psd found inside the 02 what it can do folder. These are the RGB clouds, which look somewhat better in the color department a little bit I would say but look much worse in terms of the noise department, witness most prominently up here in the upper right corner of the image and this is what we are going for.

We want to get this effect here which is just it's almost noiseless, has very little noise associated with it and it just oh, just beautiful. All right, so let's see what we can do here. Our mistake thus far as that we are relying on the Levels Command. The Levels Command is great if you only need to go so far because it's easy to use. It's little more predictable in my opinion. But you kind of top out. Whereas with the Curves Command you have a lot more flexibility but you also have a lot more to manage. So let's give it a try. I'm going to tab back my palettes here and I'm going to turn off the Levels Adjustment Layer.

You could if you wanted to. You could just go ahead and click on the Levels Adjustment Layer. You can go up to Layer menu and you could say Change Layer Content and you could choose Curves and that will transform it into a Curves Adjustment Layer. But you will lose all of your adjustments. It will start over from scratch. So what I suggest you do instead, go ahead and Cancel out. What I suggest you do is just turn it off. That way you can come back to it if you need to and then click on the original version of the image. What is now a Smart Object. Press and hold the Alt key or the Option key on the Mac, click on the black/white icon and choose Curves and by the way it's perfectly acceptable to add a bunch of adjustment layers to an image that you are not using, because they take barely any room up inside of your image file.

It only added a few K, they are very small. So I'm going to change the name of this guy to curves you know modification or something along those line and then I'm going to click OK and we are working in the Lightness Channels for starters and then there is the A and B Channels as well. Now the Curves dialog box works differently. We can't see here in Photoshop CS3. We can see a histogram in the background. So we know where to put our white and black points. So here is the Black Point. By default you should see this setup here where you are seeing black in a lower left corner and white in the upper right corner.

That's the way I prefer to work. Some people prefer to work differently but if you are going to work along with me you need to make sure, notice that I click this double down pointing arrowhead thing. You need to make sure that Show Amount of is set to Light, not Pigment. That way we are working the same way we are used to working and I'm going to go ahead drag this Black point over to the left and notice that as I do it or I could just click on Auto. That's what I will do click on Auto and then it will just automatically fix just like we did with Levels. That will automatically fix that Lightness Channel. But notice instead of setting the Input Value to 61 as it did in the case of Levels, a couple of exercises ago you may recall, it sets it to 23 and instead of setting I will go ahead and click on the White point, instead of setting it to what was it before, it was something like 221 or something I can't remember exactly what.

But it sets it to something around 80, the high 80s, the low 90s because it just kind of moved it when I clicked on it. Let's click Auto again. See what it sets. 89. Is what it sets it to. So what in the world is going on? Well, we are not working with luminance levels anymore or at least we are but it's not talking to us that way. Curves is, instead of talking to us from zero to 255, the way the Levels dialog box was talking to us, it's talking to us from zero for Black to 100 for White. So we have 101 different levels.

We actually still have the same 256 different levels it's just the values don't react in the same way. So it's a little confusing, which is another reason I kind of prefer to work with Levels. But anyway let's go back down here I'm going to Ctrl+Tab, if you press Ctrl+Tab inside the Curves dialog box and this is either a Mac or a Windows Ctrl+Tab, you will switch back and forth between points. So that you don't run the risk of like clicking on it and slightly nudging it to a different location. I'm going to change this Input Value to 21 by pressing a left arrow key a couple or three times, actually more than three times, as many times as it takes to get it down to 21.

Because every time you nudge that from the keyboard you are changing a luminance level, so have 256 different luminance levels to work with but you only have a 101 values that are going to show up here. So it's going to take you probably five presses of the left arrow key to get from 23 down to 21 there. Then what I'm going to do is I'm going to add -- well actually you know what, I'm going to Ctrl+Tab up to this white point there and let's go ahead and press the right arrow key a few times until we change the Input Value to 93.

So we are just saying anything that has an Input of 93 is going to change to an Output of a 100. So it's going to get brighter and now I'm going to add a few significant points to the graph, and the way that we do that is you just drag around inside of the image. You just click and drag around inside of the image and you follow the bouncing ball. See that bouncing ball is showing up here in the upper right-hand corner. When I drag again and that shows you that this range of colors if you want to be able to control them are around the array indicated by the bouncing ball and if you just want to add a point to that location then you Ctrl+Click or you Cmd+Click inside of the image on the Macintosh side of things.

We don't have to press the Shift key or anything the way we do in RGB. We just get a point at this location, just inside the Lightness Channel because that's the channel we are working on. You can only work in one channel at a time when you working in Lab and let's go ahead and take this guy. Right now for me it's showing up as an Input Value of 76 and Output Value of 76. What we want is an input of 75 and we want an output of 79. So you can change the values or you can just press the arrow keys. You change the Input Value, if you are pressing arrow keys. You change the Input Value by pressing the left and the right arrow keys.

You change the Output Value by pressing the up and down arrow keys and that's what I'm doing. Work any way you like to work and then let's sort of click over here in this region in order to sort of lift the color and I'm going to Ctrl or Cmd+Click right there in the section of the clouds and I get 28, 38 whatever but we wanted to be because an Input of 44 that's what's going to work best for us and how did I figure this out. Good little trial and error, I found some values that work for us. Input of 44, and Output of 32 is going to hold us in good stead here.

Now, that's not giving me as much brightness as I want down here sort of in this low level, this far distant portion of the clouds down through the bottom of the image. So I'm going to click midway between these two points right here. I'm going to click right about there in order to set a point and we want that one to be an Input of 54 and the Output Value should be 50. So I'm going to go ahead and take that down. So I took it down into the left and then finally I'm going to set another point down here just so that we can sink the darks a little bit.

I really want those clouds to be nice and dark. We want some nice shadows. Some rich shadows going on, so click right about there and we will change that guy to -- well, let's say how about 37 as I recall it's going to work out Well for us. An Input of 37 and an Output of 10. Oh, it's already set to an Output of 10. So this should work out pretty nicely. So just to review all the points we have in our lumpy looking graph here. I'm going to press Ctrl+Shift+Tab in order to go to the first.

You can go backward to the points with Ctrl+Shift+Tab forward to the points with Ctrl+Tab. So we have got 21, 0 and then we have got 37, 10. I'm reading the Input Value first and the Output Value second and then we have 44, 32 and then we have 54, 50, we have got 75, 79 and we have got 93, 100. How would you know to use such values? You would play around and try to figure it out. You can always go back, right? Click OK in order to accept those modifications.

If you change your mind later, all you have to do is double-click on this icon to bring up the Curves dialog box and play some more until you get exactly the result you want. All right, I'm going to click OK because that's enough for now. All we have done is we have transformed the luminance levels because we just changed the Lightness Channel and nothing else. In the next exercise, we are going to correct the A and B Channels. Get sight.

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This video is part of

Image for Photoshop CS3 Mastering Lab Color
Photoshop CS3 Mastering Lab Color

70 video lessons · 10737 viewers

Deke McClelland
Author

 
Expand all | Collapse all
  1. 23m 32s
    1. Your doorway to better color
      2m 18s
    2. Lab and the untreated JPEG image
      6m 15s
    3. Lab and Camera Raw with a JPEG file
      6m 5s
    4. Lab and Camera Raw with a raw photograph
      8m 54s
  2. 1h 6m
    1. Don't fear the Lab mode
      1m 5s
    2. Why color is 3D
      4m 22s
    3. Device-dependant RGB and CMYK
      5m 15s
    4. Device-dependant CIELAB D50
      5m 33s
    5. Color by the numbers (mixing Lab values)
      5m 35s
    6. The Hue/Saturation color wheel
      4m 0s
    7. The slightly skewed Lab color wheel
      9m 56s
    8. Lab's wide world of "imaginary colors"
      6m 41s
    9. Examining RGB and CMYK channels
      6m 37s
    10. The strange (but powerful) Lab channels
      6m 47s
    11. How RGB and CMYK channels blend
      6m 45s
    12. How channels blend in Lab
      3m 54s
  3. 1h 17m
    1. Bad becomes great, great becomes better
      1m 0s
    2. Cheapening a perfectly good image in RGB
      5m 3s
    3. Making a great image even better in Lab
      8m 9s
    4. Saving a Lab image file
      2m 13s
    5. Favoring yellow to balance skin tones
      6m 12s
    6. Dropping out the blues
      5m 34s
    7. Correcting a very bad image in RGB
      7m 20s
    8. Sharpening luminance independently of color
      5m 22s
    9. Correcting a very bad image in Lab
      7m 34s
    10. Sharpening the Lightness channel
      5m 47s
    11. Finessing the Lightness channel with Curves
      8m 27s
    12. Applying Curves to the a and b channels
      7m 52s
    13. Sharpening for effect, blurring away noise
      7m 14s
  4. 57m 23s
    1. The convergence of all things nondestructive
      1m 26s
    2. Correcting saturation and color cast
      8m 5s
    3. Fading the oranges and reds
      4m 32s
    4. The secret power of Brightness/Contrast in Lab
      5m 5s
    5. Smart Objects and sharpening
      3m 33s
    6. Fixing chromatic aberrations in RGB
      8m 51s
    7. Adding clarity with High Pass
      3m 13s
    8. Reducing color noise with Median
      4m 35s
    9. Protecting the sky with a density mask
      5m 48s
    10. Nondestructive cropping with Canvas Size
      6m 23s
    11. Convert to RGB, flatten, and save
      5m 52s
  5. 1h 34m
    1. Images with bigger issues
      1m 6s
    2. Fixing a color cast
      6m 14s
    3. Exaggerating a color cast
      5m 23s
    4. Quantifying and correcting a color cast
      8m 11s
    5. Sharpening an image with the Emboss command
      4m 38s
    6. Introducing a more complicated color cast
      3m 43s
    7. Drawing a custom contrast curve
      7m 21s
    8. Performing a gross color cast compensation
      3m 49s
    9. Fine-tuning a color cast compensation
      5m 52s
    10. Restoring neutral highlights
      6m 8s
    11. Masking away aberrant hues
      5m 16s
    12. Sharpen, save, convert to RGB, and crop
      6m 18s
    13. Applying a Shadows/Highlights Smart Filter
      5m 1s
    14. Tweaking Shadows/Highlights in Lab
      5m 25s
    15. Rendering Shadows/Highlights in Lab
      7m 57s
    16. Correcting color cast and contrast
      6m 16s
    17. Completing a low-frequency portrait with High Pass
      5m 22s
  6. 1h 5m
    1. Changing some colors, leaving others as is
      1m 7s
    2. Rotating hues in RGB with Hue/Saturation
      5m 0s
    3. Modifying colors in Lab with Curves
      5m 47s
    4. Blending colors with Underlying Layer
      6m 8s
    5. Changing colors in wardrobe shots
      6m 1s
    6. Blending the Red and b channels
      8m 5s
    7. Developing a base mask
      8m 8s
    8. Colorizing an isolated area
      7m 33s
    9. Revealing complementary highlights
      3m 18s
    10. Repairing strangely colored shadows
      5m 37s
    11. Tanning and deepening skin tones
      4m 13s
    12. Exposing bright eyes and teeth
      4m 39s
  7. 1m 8s
    1. See ya
      1m 8s

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