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Photoshop CS4: Image Adjustments in Depth
Illustration by John Hersey

Reading the Histogram panel


From:

Photoshop CS4: Image Adjustments in Depth

with Jan Kabili

Video: Reading the Histogram panel

Before you correct the tonality of an image it's important to diagnose the problem that you want to correct. It takes practice to train your eye to read the tonal values in a photograph and even if you are skilled in the art of reading photographs, there will be times when you'll find it hard to determine what's wrong with an image by relying on visual cues alone. That's when the Histogram panel can really come in handy. The Histogram panel offers an invaluable way to evaluate photographs to diagnose problems that you want to correct and to monitor the effects of adjustments as you make them.
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  1. 5m 39s
    1. Welcome
      1m 18s
    2. Using the exercise files
      59s
    3. Setting up a workspace
      3m 22s
  2. 21m 2s
    1. Creating and editing adjustment layers
      6m 38s
    2. Adjustment layers vs. direct adjustments
      6m 9s
    3. Using the new Adjustments panel
      5m 38s
    4. Reusing adjustment layers
      2m 37s
  3. 39m 57s
    1. Clipping adjustment layers
      4m 36s
    2. Including adjustment layers in a layer group
      3m 13s
    3. Including adjustment layers in a Smart Object
      7m 29s
    4. Using the adjustment layer mask
      5m 43s
    5. Using selections with adjustment layers
      4m 19s
    6. Using the Masks panel with adjustment layers
      8m 30s
    7. Using the Blend If sliders with adjustment layers
      6m 7s
  4. 49m 43s
    1. Reading the Histogram panel
      5m 23s
    2. Using the Levels adjustment for tonal corrections
      7m 42s
    3. Using the Curves adjustment for exposure
      8m 12s
    4. Using the Curves adjustment for contrast
      4m 14s
    5. Making On-Click Curves adjustments
      4m 0s
    6. Applying Shadow/Highlight nondestructively
      7m 59s
    7. Reviewing Brightness/Contrast
      3m 18s
    8. Dealing with exposure
      2m 22s
    9. Using adjustment layers with blend modes
      6m 33s
  5. 54m 36s
    1. Making Vibrance adjustments
      2m 22s
    2. Using Hue/Saturation adjustments
      7m 4s
    3. Understanding color correction
      3m 21s
    4. Using color samplers and the Info panel
      4m 25s
    5. Using Levels eyedroppers for color correction
      5m 54s
    6. Using Levels channels for color correction
      5m 7s
    7. Understanding Curves adjustments for color correction
      7m 21s
    8. Making Color Balance adjustments
      3m 49s
    9. Making Photo Filter adjustments
      3m 6s
    10. Making Variations adjustments
      6m 48s
    11. Using the auto-correction features
      5m 19s
  6. 13m 5s
    1. Using the Dodge and Burn tools
      4m 56s
    2. Dodging and burning nondestructively
      6m 38s
    3. Working with the Red-Eye tool
      1m 31s
  7. 16m 9s
    1. Applying Black & White adjustments
      7m 30s
    2. Making Channel Mixer adjustments
      6m 31s
    3. Understanding the Threshold adjustment
      2m 8s
  8. 25m 23s
    1. Colorizing with Hue/Saturation adjustments
      3m 9s
    2. Tinting with Black & White adjustments
      2m 8s
    3. Making a Gradient Map adjustment
      4m 18s
    4. Applying a Selective Color adjustment
      1m 49s
    5. Using the Replace Color adjustment
      4m 39s
    6. Making Match Color adjustments
      4m 24s
    7. Applying the Equalize adjustment
      4m 56s
  9. 42s
    1. Goodbye
      42s

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Photoshop CS4: Image Adjustments in Depth
3h 46m Intermediate Jun 10, 2009

Viewers: in countries Watching now:

Photoshop CS4's adjustment features offer unparalleled opportunities to correct and manipulate images. In Photoshop CS4: Image Adjustments in Depth, Jan Kabili explains how to use all the major Photoshop adjustment features. She shares the best techniques for adjusting image quality, and shows how to use the new Adjustments panel to streamline a photo correction workflow. Jan also demonstrates multiple ways to eliminate color casts, and explains how to use the new On-Image Curves control to adjust brightness and color. This course offers a detailed look at the techniques photographers and designers use to master image adjustments in Photoshop. Exercise files accompany the course.

Topics include:
  • Using adjustment layers in a non-destructive image-editing workflow
  • Correcting color with curves
  • Adjusting brightness and contrast with levels
  • Dodging and burning photographs
  • Reading histograms accurately
  • Converting color images to grayscale with a Black & White adjustment layer
  • Customizing auto-corrections for more accurate quick adjustments
Subjects:
Design Photography
Software:
Photoshop
Author:
Jan Kabili

Reading the Histogram panel

Before you correct the tonality of an image it's important to diagnose the problem that you want to correct. It takes practice to train your eye to read the tonal values in a photograph and even if you are skilled in the art of reading photographs, there will be times when you'll find it hard to determine what's wrong with an image by relying on visual cues alone. That's when the Histogram panel can really come in handy. The Histogram panel offers an invaluable way to evaluate photographs to diagnose problems that you want to correct and to monitor the effects of adjustments as you make them.

Let's start by opening the Histogram panel. You can do that by going up to the Window menu at the top of the screen and choosing Histogram or as I did, you can change you workspace to one that includes the Histogram panel like the Color and Tone workspace. By default the Histogram panel looks like this when you open it. I prefer to see it larger and so I like to go the panel menu on the right side of the Histogram panel group and choose Expanded View. In Expanded View I have a menu up here that I can use to change the way the channels in the image are represented.

By default the Histogram panel represents each one of the Color Channels in the image. I think it's easier to read the Histogram, if you go into the channel menu and you choose RGB instead which presents a composite view of the Red Green and Blue channels in an open image. The Histogram in this panel is basically a diagram or a bar chart of the tonal values in the open image. The left side of the Histogram represents the darkest tones in the image and the right side of the Histogram represents the brightest tones in the image.

The mound in between represents the Gray values in between the brights and the darks. If you could pull this mound apart, you'd see that it's made up of individual vertical bars. And each vertical bar represents a particular shade of Gray in the image. The height of a bar varies with the relative frequency of its tone in the open image. A tall bar like these in the middle of this histogram mean that there is lots of that particular tone in the open image. If there are no bars, in an area of the image or very few like those over here on the right, it means that there is not much of the corresponding tone in the image, so in this particular image, there isn't much white.

Many photographs look best if they have a wide range of tones and good contrast between the blacks and the whites, like this photograph does. So it's often your goal to expand the tonal range of a photograph as you are adjusting it. Now let me show you an image that doesn't have such a good tonal range. I'm going to click on lifeguard.psd, which is open in this tab. This image looks pretty flat when you view it and if you go over to the Histogram panel you can see why. There are lots of Gray pixels in the image and some dark pixels as well but there are no bright pixels at all. And that means there is very little contrast in the image because contrast refers to the difference between the bright brights in an image and the dark darks.

This could probably be fixed with an adjustment like Curves or Levels but before you apply an adjustment like that, you need to analyze what the problem is and the Histogram panel can help you with that. Now let's look at another image restaurant.psd which is also open here. In the histogram, it looks like there is a pretty good tonal range in this image from darks all the way over to brights. But there's one thing about this histogram to be wary of and that's the spike over here on the far right. A spike like this means that that area of the photo is clipped.

In other words, in this case, that the detail in these highlight areas is missing from the photograph. If you happen to be adjusting a photograph and you notice a spike either on the right side representing clipped highlights or on the left side representing clipped shadow areas, you might want to pull back a bit and your adjustment to avoid losing detail in those areas. Let's look at one more image, fence.psd. I'm showing you this image because by default the histogram represents the tones in an entire image. But if you want to, you can change the histogram to represent the tones in just a single layer.

I'm going to go down to the Layers panel here which has collapsed to make room for the histogram panel and I'll Double-click the Layers tab to expand the Layers panel again. Here you can see that there are two layers in this file. The foreground layer, which contains all this foreground image along with some transparent pixels, and the sky layer, which contains just the dark sky and some transparent pixels. Now if I select the sky layer in the Layers panel and I then go up to the Histogram panel, look how the histogram changes. If I change the Source of the Histogram from the Entire Image where there's a wide range of tones to the selected Sky layer. The histogram is now confirming that in the sky layer most of the pixels are gray or dark and there are no light areas at all. You can use this information if you are adjusting just the sky.

So as you can see the histogram is a really useful tool which can help you to evaluate an image before you adjust it and to understand the effects of your adjustments on an image as you make them. If you do have room on your screen, I'll suggest you always try to keep the valuable Histogram panel open whenever you are adjusting tone in an image.

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