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A little color theory

From: Photoshop CS5: Landscape Photography

Video: A little color theory

Some of the editing concepts that we're going to cover later will be easier to understand if you know a few rudiments of color theory. As you may remember from biology class, your eyes have two types of light-sensitive cells in them: rods and cones. Rods comprise your night vision. They are your black and white low-light vision. They are what 98% of your vision is made of. You also have cones, which are cells that are sensitive to color. What you may not remember from biology class is that there are three different types of cones.

A little color theory

Some of the editing concepts that we're going to cover later will be easier to understand if you know a few rudiments of color theory. As you may remember from biology class, your eyes have two types of light-sensitive cells in them: rods and cones. Rods comprise your night vision. They are your black and white low-light vision. They are what 98% of your vision is made of. You also have cones, which are cells that are sensitive to color. What you may not remember from biology class is that there are three different types of cones.

Some are sensitive to red, some are sensitive to green, and some are sensitive to blue. These colors are significant because they are the primary colors of light. When you mix them together, you can get any other color. Here is an example. I have three circles: one filled with blue, one filled with green, and one filled with red. Where red and blue mixed together, I get magenta. Where blue and green mixed together, I get cyan. Where green and red mixed together, I get yellow. I can mix these in an infinite variety of combinations to get every other color in between.

If I mix equal amounts of all three, I get white. Now you may be thinking, "Well, in finger -painting class, I remember that when I mixed colors together, everything got darker until it just turned into this kind of brown sludgy thing." That's because pigments work subtractively. As you mix them together, they get darker. Light works additively. These are known as the additive primary colors of light, because they mix together to add up to white. The reason we care about this is because some image-editing problems are easier to diagnose with an understanding of how different color channels come to bear on your image.

Sometimes, we will attack problems by looking its specific color channels. In Photoshop, I can go to the Channels palette, which lets me look at specific color channels in my image. Right now, I'm looking at RGB, but if I click on the Red channel, I'm now looking at only the red channel. What I see here is a white circle on a field of black. Where white pixels occur, it means 100% red; where black pixels occur, it means no red at all. Same thing for green and same thing for blue.

When I look at the final image, I see that, sure enough, there is 100% red in these pixels, 100% green here. They are mixing together to create this yellow. Let's take a look at a more real-world example. Here is an image with a fair amount of color in it. We've got some blue up here, some reds down here, a lot of browns over here. If I go and look at the Red channel, I find this. It appears to be a black-and-white image, just the way our last example was. These red posts are showing up predominately as white, because as you will recall, 100% white in the Red channel equates to red in the image.

So it makes sense that these red things would appear as white in the Red channel. Let's go look at the Green channel, and now these red posts, in my final image, appear much darker, because there is very little green in them. I'll switch back to RGB to view my whole image. So, one of the most important things for you to do before we get started here is to make sure that your histogram is set up in a way that you understand, because the histogram in Photoshop has the ability to show you separate histograms for each color channel.

I'm going to go to the Window menu and choose Histogram. This is the Histogram we were looking at earlier. It is just showing luminance, or brightness. In other words, it's showing the distribution of tones from darkest to lightest. Again, we see that I don't have strong highlight detail here, mostly midtone data, perhaps a little low contrast. If I open up this pop-up menu up here and choose Expanded View, I get some additional controls, including this Channels pop-up. Now, by default, your Channel pop-up may be set to something different than this RGB view.

It's probably set to Colors. Now I see this. I see three different histograms, and where they're overlapping, I see some secondary histograms. So you can plainly see back here the blue histogram. You can see hints of the red histogram and a couple of hints of the green histogram. There is also a little bit of magenta, cyan, and yellow in here. These are showing the separate histograms for the separate color channels, in other words, the distribution of individual color channels in the image. So you can see in the lighter tones, there's more blue than anything else.

If you're wondering what this exclamation mark means, it means that the histogram is not necessarily up-to-date for this image. If I click on it, Photoshop will take some time to calculate a more accurate histogram. So, when you're getting ready to do a critical histogram-driven work, it's a good idea to click on that exclamation mark. We'll be returning a lot to Channels and Histograms throughout this course, so you'll get more practice with them, and they should become easier to deal with as we go along.

Show transcript

This video is part of

Image for Photoshop CS5: Landscape Photography
Photoshop CS5: Landscape Photography

59 video lessons · 22150 viewers

Ben Long
Author

 
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  1. 3m 14s
    1. Welcome
      1m 44s
    2. Using the exercise files
      1m 30s
  2. 46m 35s
    1. Defining landscape photography
      2m 23s
    2. Considering cameras and gear
      10m 41s
    3. Shooting and composition tips
      6m 39s
    4. Why you should shoot raw instead of JPEG
      4m 25s
    5. Making selects
      10m 42s
    6. Understanding the histogram
      6m 53s
    7. A little color theory
      4m 52s
  3. 1h 14m
    1. Opening an image
      4m 42s
    2. Cropping and straightening
      9m 56s
    3. Nondestructive editing
      6m 23s
    4. Spotting and cleanup
      3m 53s
    5. Cleaning the camera sensor
      11m 17s
    6. Lens correction
      6m 26s
    7. Correcting overexposed highlights
      7m 29s
    8. Basic tonal correction
      5m 45s
    9. Correcting blacks
      11m 54s
    10. Correcting white balance
      6m 35s
  4. 21m 34s
    1. Performing localized edits with the Gradient Filter tool
      7m 24s
    2. Performing localized edits with the Adjustment brush
      7m 54s
    3. Controlling brush and gradient edits
      6m 16s
  5. 16m 34s
    1. Working with noise reduction
      5m 33s
    2. Clarity and sharpening
      5m 23s
    3. Exiting Camera Raw
      5m 38s
  6. 58m 5s
    1. Retouching
      8m 23s
    2. Using Levels adjustment layers
      10m 59s
    3. Saving images with adjustment layers
      4m 18s
    4. Advanced Levels adjustment layers
      9m 36s
    5. Guiding the viewer's eye with Levels
      8m 48s
    6. Using gradient masks for multiple adjustments
      5m 32s
    7. Correcting color in JPEG images
      3m 15s
    8. Adding a vignette
      3m 25s
    9. Knowing when edits have gone too far
      3m 49s
  7. 33m 24s
    1. Preparing to stitch
      5m 59s
    2. Stitching
      7m 39s
    3. Panoramic touchup
      7m 17s
    4. Shooting a panorama
      4m 58s
    5. Stitching a panorama
      7m 31s
  8. 27m 18s
    1. Shooting an HDR Image
      7m 53s
    2. Merging with HDR Pro
      11m 52s
    3. Adjusting and retouching
      7m 33s
  9. 24m 4s
    1. Why use black and white for images?
      2m 26s
    2. Black-and-white conversion
      7m 13s
    3. Correcting tone in black-and-white images
      7m 38s
    4. Adding highlights to black-and-white images
      6m 47s
  10. 49m 32s
    1. Painting light and shadow pt. 1
      11m 22s
    2. Painting light and shadow pt. 2
      12m 42s
    3. Painting light and shadow pt. 3
      9m 19s
    4. HDR + LDR
      5m 7s
    5. Reviewing sample images for inspiration
      11m 2s
  11. 48m 2s
    1. Sizing
      9m 8s
    2. Enlarging and reducing
      5m 3s
    3. Saving
      1m 24s
    4. Sharpening
      8m 23s
    5. Outputting an electronic file
      9m 4s
    6. Making a web gallery
      4m 17s
    7. Printing
      10m 43s
  12. 20s
    1. Goodbye
      20s

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