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Introducing the histogram

From: Photoshop CS6 One-on-One: Fundamentals

Video: Introducing the histogram

In this movie, I'll introduce you to another way to gauge the luminance levels inside your image and it's called a histogram. Now at first it might seem quite technical, but once you come to terms with the histogram, luminance levels make that much more sense. Now to see the histogram, you go onto the Window menu and you choose the Histogram command which brings up the Histogram panel. Now what this is, it's a bar graph of the various luminance levels inside the image. You may see it in color. You may see it in white. To make things a little less confusing, what I'd like you to do is click on the flyout menu icon and choose Expanded View in order to increase the size of the graph, and then go ahead and switch the Channel from Colors to Luminosity, so we can see the core luminance levels inside the image.

Introducing the histogram

In this movie, I'll introduce you to another way to gauge the luminance levels inside your image and it's called a histogram. Now at first it might seem quite technical, but once you come to terms with the histogram, luminance levels make that much more sense. Now to see the histogram, you go onto the Window menu and you choose the Histogram command which brings up the Histogram panel. Now what this is, it's a bar graph of the various luminance levels inside the image. You may see it in color. You may see it in white. To make things a little less confusing, what I'd like you to do is click on the flyout menu icon and choose Expanded View in order to increase the size of the graph, and then go ahead and switch the Channel from Colors to Luminosity, so we can see the core luminance levels inside the image.

Now at first glance you may look at this thing and think how in the world is this going to benefit me? Well I've created a diagram of a histogram for you and I'll walk you through it so that it makes more sense. I'm going to hide the Histogram panel for now. We'll come back to it in the next movie when I show you a practical application of the function. And I'm going to switch to this image called histogram.psd again, found inside the 07_luminance folder, and I'm going to press Shift+F. By the way, you can back up through the Full Screen modes by pressing the Shift Key along with F and that'll take me directly to full screen as you see here.

And this is a big diagram of a histogram. Here's how it works. This is a bar graph of the luminance levels inside of your image, starting with black over here in the far left-hand side, and going all the way over to white on the far right-hand side. And so it's ultimately a kind of popularity contest; the taller the line the more of that specific luminance level you have. To get even more technical, your standard digital image is an 8-bit per channel image.

What that means is you have up to 256 different luminance levels, including black and white, and all the other luminance levels in between, per channel. Some images have more than that but that's the standard. And so if you were to take a careful look at the histogram and count up all of these bars here, you'd find that there are a total of 256 bars in all. Each one of these luminance levels has a specific numerical value associated with it.

Black is 0 and White is 255. Now that may not make sense. After all, I just told you there are 256 luminance levels in all. How is it that white at 255, plus black at 0, adds up to 256? Well it's because black is yet another luminance level that's just sitting there at 0. So you've got 1 through 255, plus black at zero. That gives you 256 in all.

Now when you're reading the histogram, this area over here is going to be the shadows, as I've labeled, so the left- hand side, that's where the shadows are at; the highlights are going to appear over here on the right-hand side; and then the midtones are going to appear in the middle of the graph. And again, these are just rough general definitions of those regions of luminance level. What you want to see is that the graph pretty much starts right at the beginning here and slopes up, and then we have a healthy amount of shadow detail.

You also want to see over here in the right-hand side that the graph amps up at white and that we have a healthy number of highlights going on, and then finally, you want to see a lot of bouncing inside the midtones. What you don't want is to see a big spike right there at black or a big spike right there at white with relatively little action going on in the middle of the graph, because what that tells you is that you have a lot of clipped shadows and you have a lot of clipped highlights, and when you run into an image like that you can make it look a little better, but you're never going to make it look great.

It's pretty much a failed image from the get-go, and you certainly don't want to take an image that has a histogram like this one, a nice healthy histogram that is, and turn it into one where the middle of the graph is very low and then you have spikes at either side. And of course as with any bar graphs, small bars mean you have few luminance levels at that location and big bars mean you have lots of luminance levels. Now by lots I don't mean any specific value, because Photoshop goes ahead and scales the histogram according to how many luminance levels it finds throughout the entire image.

And so that's how the histogram works. You'll find it inside the Histogram panel. You find it elsewhere inside the software, as well. And once you get a sense for how it works, it's an extremely helpful tool. And I'll show you how to use the histogram to gauge the quality of your correction in the next movie.

Show transcript

This video is part of

Image for Photoshop CS6 One-on-One: Fundamentals
Photoshop CS6 One-on-One: Fundamentals

100 video lessons · 56116 viewers

Deke McClelland
Author

 
Expand all | Collapse all
  1. 19m 15s
    1. Welcome to One-on-One
      2m 27s
    2. Opening from the Windows desktop
      4m 7s
    3. Opening from the Macintosh Finder
      4m 9s
    4. Opening from Photoshop or Bridge
      2m 45s
    5. Opening an image from Mini Bridge
      1m 16s
    6. Opening through Camera Raw
      2m 32s
    7. Closing one image and Closing All
      1m 59s
  2. 38m 14s
    1. Navigating your image
      40s
    2. The dark vs. the light interface
      3m 12s
    3. Navigating tabs and windows
      4m 32s
    4. Panels and workspaces
      4m 27s
    5. Zooming incrementally
      4m 29s
    6. Zooming continuously
      2m 43s
    7. Entering a custom zoom value
      2m 25s
    8. Scrolling and panning images
      2m 31s
    9. Rotating and resetting the view
      2m 11s
    10. Cycling between screen modes
      3m 10s
    11. Using the Navigator panel
      3m 38s
    12. Adjusting a few screen prefs
      4m 16s
  3. 45m 58s
    1. Digital imaging fundamentals
      1m 45s
    2. Image size and resolution
      3m 3s
    3. The Image Size command
      3m 27s
    4. Common resolution standards
      3m 20s
    5. Upsampling vs. real pixels
      4m 36s
    6. Changing the print size
      6m 16s
    7. Downsampling for print
      4m 12s
    8. Downsampling for email
      3m 11s
    9. The interpolation settings
      5m 22s
    10. Downsampling advice
      4m 36s
    11. Upsampling advice
      6m 10s
  4. 53m 17s
    1. The layered composition
      1m 40s
    2. Introducing the Layers panel
      4m 12s
    3. Adding, scaling, and aligning layers
      5m 27s
    4. Dragging and dropping layers
      4m 36s
    5. Stack, reveal, and rename
      2m 58s
    6. Opacity, history, and blend mode
      6m 5s
    7. Duplicating a selected portion of a layer
      5m 32s
    8. Applying a clipping mask
      3m 58s
    9. Blending inside a clipping mask
      4m 10s
    10. Finishing off your artwork
      3m 13s
    11. Creating a new layer and background
      4m 24s
    12. Layering tips and tricks
      7m 2s
  5. 26m 19s
    1. The art of saving
      54s
    2. Four things to know about saving
      6m 0s
    3. Saving layers to PSD
      6m 38s
    4. Saving print images to TIFF
      4m 48s
    5. Saving an interactive image to PNG
      3m 41s
    6. Saving a flat photo to JPEG
      4m 18s
  6. 19m 36s
    1. Honing in on your image
      1m 43s
    2. The new and improved Crop tool
      3m 35s
    3. Editing your last crop
      3m 1s
    4. Straightening a crooked image
      2m 29s
    5. Filling in missing details
      6m 44s
    6. Using the Perspective Crop tool
      2m 4s
  7. 42m 6s
    1. First, there is brightness
      2m 12s
    2. How luminance works
      4m 18s
    3. The three Auto commands
      3m 27s
    4. Automatic brightness and contrast
      3m 19s
    5. The Brightness/Contrast command
      2m 47s
    6. The dynamic adjustment layer
      4m 5s
    7. Editing adjustment layers
      3m 52s
    8. Isolating an adjustment with a layer mask
      3m 31s
    9. Introducing the histogram
      4m 58s
    10. Measuring an adjustment
      3m 34s
    11. Using the Shadows/Highlights command
      6m 3s
  8. 44m 33s
    1. And second, there is color
      1m 31s
    2. Identifying a color cast
      3m 34s
    3. Correcting a color cast automatically
      3m 57s
    4. Changing the color balance
      6m 10s
    5. Compensating with Photo Filter
      3m 11s
    6. Adjusting color intensity with Vibrance
      3m 29s
    7. Correcting color cast in Camera Raw
      5m 46s
    8. The Hue/Saturation command
      5m 26s
    9. Summoning colors where none exist
      4m 8s
    10. Making more color with Vibrance
      4m 27s
    11. Making a quick-and-dirty sepia tone
      2m 54s
  9. 55m 46s
    1. Making selective modifications
      1m 10s
    2. The geometric Marquee tools
      6m 1s
    3. Aligning one image element to another
      4m 59s
    4. The freeform Lasso tools
      3m 59s
    5. Polygonal Lasso tool and Quick Mask
      5m 19s
    6. Cropping one selection inside another
      6m 15s
    7. Creating rays of light
      4m 44s
    8. Quick Selection and Similar
      4m 11s
    9. Making it better with Refine Edge
      4m 56s
    10. Integrating image elements
      2m 39s
    11. Magic Wand and Grow
      5m 17s
    12. Refine, integrate, and complete
      6m 16s
  10. 53m 49s
    1. Your best face forward
      1m 0s
    2. Content-Aware Fill
      6m 11s
    3. Using the Spot Healing Brush
      5m 36s
    4. The more capable "standard" Healing Brush
      5m 55s
    5. Meet the Clone Source panel
      3m 53s
    6. Caps Lock and Fade
      4m 57s
    7. The Dodge and Burn tools
      5m 1s
    8. Adjusting color with the Brush tool
      6m 35s
    9. Smoothing skin textures
      5m 58s
    10. Brightening teeth
      4m 0s
    11. Intensifying eyes
      4m 43s
  11. 51s
    1. Goodbye
      51s

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