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Understanding grayscale values and channels

From: Scanning Techniques for Photography, Art, and Design

Video: Understanding grayscale values and channels

In this movie I would like to expand our understanding of grayscale values in Channels. In previous movies we talked about the basic building blocks of a digital image, what does a scanner or a digital camera capture, we saw that it captures pixels. We talked about the fact that depending upon the scan mode that you choose you'll end up with single or multiple channels and you can have black-and-white simple black-and-white or grayscale values in pixels that your scanner or digital camera captures. And what I'd like to do here is develop that whole concept of grayscale value in channels and that number we actually put in those grayscale values.

Understanding grayscale values and channels

In this movie I would like to expand our understanding of grayscale values in Channels. In previous movies we talked about the basic building blocks of a digital image, what does a scanner or a digital camera capture, we saw that it captures pixels. We talked about the fact that depending upon the scan mode that you choose you'll end up with single or multiple channels and you can have black-and-white simple black-and-white or grayscale values in pixels that your scanner or digital camera captures. And what I'd like to do here is develop that whole concept of grayscale value in channels and that number we actually put in those grayscale values.

So I have zoomed in here on this Blue- Green cape and it's very, very colorful image, and just to review when you capture a "color image" what the scanner or digital camera actually captures is three grayscale channels that we call Red, Green, and Blue, but as we see here they are really nothing, but grayscale, because that's all a digital camera or digital scanner can capture. And where does this color come from? Remember that all colors created by output devices. In this case the monitor on which you are viewing this image actually applies Red, Green, and Blue colors to these grayscale pixels and the amount of Red, Green, and Blue that are size of the pixels depends upon the grayscale value that's on the Red, the Green, and the Blue channel.

So let's take a look at an individual pixel and here I am going to use my Info tool in Photoshop, that's the I for Info tool, and I am setting a Point Sample, so I am just measuring one pixel at a time. Normally when we're scanning or correcting images we'll do an average number of pixels, but in this case I just want to look at individual pixels. So I am going to zoom in just a little bit more. I see you can really see that we're just looking at one pixel. Now look at the grayscale value of that pixel, we'll do that by looking at their, remember, "color image" RGB values that we see over here, so when I look at the Info panel, the Red is 115, the Green is 140, and the Blue is 137.

Now with these grayscale values going to scale of 0 to 255 where 0 is Black and 255 is pure White, and we look at the ratio of these numbers, look at the Green and the Blue is higher than the Red which certainly makes sense, right, because this is a Green, Blue cape if you will. But what do these numbers actually mean? I am going to go through these three channels. I am just going to do it from my keyboard shortcuts. I am going to use Command or Ctrl+3, 4, and 5, as you see in the Channels panel, so that I don't move my tool from looking at that one pixel.

So I am going go to the Red channel and look at the Red value in the Info panel right after. It's at 115. Notice when I activate just the Red panel notice the number is 115. Let's go back to the RGB. Now the Green Channel is 140, so if we activate the Green Channel it's 140, back to RGB view, Blue is 137, guess what, when we go to just the Blue Channel everything is 137. So when you're looking at the Red, Green, and Blue values what we're really seeing is the grayscale value in each of those channels. The reason why this is so important to really understand is that when we're going to be controlling our scanners, we're actually going to be controlling the grayscale values that make up these RGB images on each of the three channels.

So this is on a scale of 0 to 255 where 255 is pure white, 0 is pure black, means the absence of that color. In as we have here in this Green, Blue image, the Green, Blue values will be higher than the Red because there is more Green and Blue than there is Red in this image. So it's all grayscale values that we're going to be capturing, editing, and manipulating during the scan process.

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This video is part of

Image for Scanning Techniques for Photography, Art, and Design
Scanning Techniques for Photography, Art, and Design

58 video lessons · 8310 viewers

Taz Tally
Author

 
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  1. 6m 48s
    1. Welcome
      1m 11s
    2. What you should know before watching this course
      3m 54s
    3. Using the exercise files
      1m 43s
  2. 1h 0m
    1. Scanners and digital cameras
      3m 6s
    2. Types of scanners
      5m 2s
    3. Scanner location
      3m 19s
    4. What scanners and digital cameras create
      7m 22s
    5. Understanding grayscale values and channels
      3m 19s
    6. Understanding pixels and vectors
      4m 1s
    7. Choosing pixels or vectors
      2m 27s
    8. Resolving resolution
      6m 32s
    9. Working with interpolation
      3m 31s
    10. Understanding the effects of compression
      2m 4s
    11. Evaluating and correcting images with histograms
      8m 26s
    12. Saving to different file formats
      7m 4s
    13. Color management
      4m 23s
  3. 33m 22s
    1. Cleaning your scanner
      7m 31s
    2. Cleaning your images
      7m 47s
    3. Calibrating your scanner
      9m 13s
    4. Creating and applying a color management profile
      8m 51s
  4. 20m 55s
    1. Evaluating your scan challenges
      9m 46s
    2. Reproducing vs. assigning colors
      6m 20s
    3. Recognizing continuous tone (contone) vs. dot pattern images
      4m 49s
  5. 36m 32s
    1. Understanding bit depth
      8m 49s
    2. Selecting a scan mode
      8m 20s
    3. Sharpening and its effects
      10m 40s
    4. Creating and assigning color management profiles
      8m 43s
  6. 2h 25m
    1. Taking the Tazmanian Oath!
      3m 38s
    2. Choosing your weapon
      4m 2s
    3. Setting up your scanning preferences
      12m 14s
    4. Performing a prescan
      2m 53s
    5. Assigning a scan frame
      5m 40s
    6. Determining scan resolution
      7m 57s
    7. Choosing a scan mode and bit depth
      5m 53s
    8. Naming images
      1m 49s
    9. Scanning simple logos and line art
      12m 21s
    10. Scanning complex line art
      7m 33s
    11. Scanning grayscale contones
      13m 22s
    12. Scanning color contones
      13m 54s
    13. Sharpening
      9m 39s
    14. Scanning printed/screened or patterned images
      7m 1s
    15. Scanning positive transparency film
      12m 33s
    16. Scanning negative transparency film
      9m 11s
    17. Capturing high dynamic range (HDR) scans
      1m 47s
    18. Setting up wet scans
      14m 29s
  7. 1h 48m
    1. Scanning, converting, and using simple line art
      5m 32s
    2. Scanning and using detailed line art
      10m 52s
    3. Scanning landscapes
      15m 50s
    4. Scanning product shots
      11m 58s
    5. Scanning combo/complex images
      9m 3s
    6. Adjusting distressed images
      11m 12s
    7. Scanning images with no neutrals
      11m 57s
    8. Post-scan touch-ups
      2m 7s
    9. Scanning images for multiple uses
      10m 44s
    10. Automatic scanning
      10m 40s
    11. Streamlining big jobs with batch scanning
      5m 22s
    12. Using your manufacturer's scanning software
      3m 14s
  8. 27s
    1. Goodbye
      27s

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