1. © 2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.
"Digital Media Primer" Yue-Ling Wong, Copyright (c)2016 by Pearson Education, Inc. All rights reserved.
© 2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

2. Chapter 3 Capturing and Editing Digital Images
Part 1
Digitizing Images by Scanning
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3. In this lecture, you will find answers to these questions
What is dpi?
What is the best scanning resolution?
What is involved to capture a digital image by scanning?
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Types of Scanners
Flatbed
Sheet-fed
Handheld
Drum
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Scanner Resolution
Optical resolution
Enhanced resolution
Reported in dpi (dots per inch)
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6. To see what "dots" in dpi stands for, let's look at how scanners work.
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How Scanners Work
A flatbed scanner has a moving scan head.
A scan head contains an array (or a row) of light sensors.
The scan head moves across the scanner bed during scanning. Its movement is controlled by a stepper motor.
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Dot
Each sensor will produce a sample (a color value) corresponding to a position of the picture being scanned.
A sensor: a dot
Each sample (color value) results in a pixel in the scanned image.
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Dot vs. Pixel
Generally speaking, a dot (sensor) produces a sample (pixel).
But a dot is not a pixel.
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A scan head only have one row of sensor. So how can it produce color values for a whole picture?
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Here is how
Get a row of color values
Move the scan head forward a little bit
Get another row of color values .
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Sampling
Recall sampling and sampling rate in the sampling step in digitization.
Sampling rate in the x-direction of a picture: The number of sensors available in the row
Sampling rate in the y-direction of a picture: The discrete stepwise movement of the scan head
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13. Determining Scanning Resolution
How the scanned image will be used:
Print
physical dimensions of the image
requirement of the printing device (e.g. printing resolution)
Web or on-screen display
pixel dimensions of the image
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14. Determining Scanning Resolution
Basic steps:
Determine the pixel dimensions of the final image
Determine the scanning resolution
(pixel dimensions from step 1) / (physical dimensions of your picture)
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15. Determining Scanning Resolution for Web or On-screen Display Example
Suppose:
the monitor resolution of your target audience is 1600  1050 pixels
you want your image to appear about ½ the width and height of the screen
your original picture is 5"  4"
Step 1.
The pixel dimensions of your final image should be 800  525 pixels.
Step 2.
Scanning resolution based on the width = 800 pixels / 5"  1 dot/pixel = 160 dpi
Scanning resolution based on the height = 525 pixels / 4 "  1 dot/pixel = 131 dpi
We will pick the highest dpi of the two, i.e., 160 dpi
With 160 dpi, your final image will have the pixel dimensions:
5"  160 dpi  1 pixel/dot = 800 pixels
4"  160 dpi  1 pixel/dot = 640 pixels
If you want exactly 800  525 pixels, you will need to crop the final image.
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16. Determining Scanning Resolution for Print Example
Suppose:
your original picture is 5"  4"
you want to scan the picture to print as 13"  10" at 300 ppi
Step 1.
The pixel dimensions of your final image should be:
13"  300 ppi = 3900 pixels
10"  300 ppi = 3000 pixels
Step 2.
Scanning resolution based on the width = 3900 pixels / 5"  1 dot/pixel = 780 dpi
Scanning resolution based on the height = 3000 pixels / 4 "  1 dot/pixel = 750 dpi
We will pick the highest dpi of the two, i.e., 780 dpi.
You may also round it up to 800 dpi.
With 780 dpi, your final image will have the pixel dimensions:
5"  780 dpi  1 pixel/dot = 3900 pixels
4"  780 dpi  1 pixel/dot = 3120 pixels
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17. Determining Scanning Resolution for Print Example
The final image 3900  3120 pixels will be printed in these physical dimensions: 3900 pixels / 300 ppi = 13" 3120 pixels / 300 ppi = 10.4" If you want exactly 13"  10", you will need to crop the final image.
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18. Tonal Adjustments During Scanning
Maximize tonal range during scanning
Any tonal ranges cropped off during scanning will not be recovered after scanning
Tonal range adjustment and histograms will be explained later in the chapter.
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19. Tonal Range Maximized During Scanning
histogram
use maximized tonal range
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20. Use Narrow Tonal Range During Scanning
histogram
use narrow tonal range
Missing very dark and very bright tones.
Looks dull and low in contrast.
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21. Crop off Highlights During Scanning
histogram
crop off highlights
The brightest areas all become white.
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Also see the interactive tutorial:
Tonal Adjustments During Scanning
An interactive tutorial that explains and demonstrates why tonal optimization is necessary during scanning.
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Review Questions
Note to instructor:
Depending on your preference, you may want to go over the review questions at the end of this lecture as an instant review or at the beginning of next lecture to refresh students' memory of this lecture.
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Review Question
True/False: The optimization of tonal adjustment at the time of capturing images--scanning or digital photography--does not matter because you can always extend the tonal range of the image to any extent afterwards in image editing applications, such as Photoshop.
False
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25. © 2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.
Review Question
Suppose that you scan a 2"  1" picture in at a resolution of 300 dpi.
What are the pixel dimensions of the scanned image? ___ pixels  ___ pixels
(i) 600  300 because 2"  300 dpi  1 pixel/dot = 600 pixels, and 1"  300 dpi  1 pixel/dot = 300 pixels
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Review Question
Suppose that you scan a 2"  1" picture in at a resolution of 300 dpi.
What are the pixel dimensions of the scanned image? ___ pixels  ___ pixels
What will the physical dimensions of the image be if you print it at 300 ppi? ___" ___"
(i) 600  300 because 2"  300 dpi  1 pixel/dot = 600 pixels, and 1"  300 dpi  1 pixel/dot = 300 pixels
(ii) 2" x 1" because 600 pixels / 300 ppi = 2", and 300 pixels / 300 ppi = 1"
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27. © 2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.
Review Question
Suppose that you scan a 2"  1" picture in at a resolution of 300 dpi.
What are the pixel dimensions of the scanned image? ___ pixels  ___ pixels
What will the physical dimensions of the image be if you print it at 300 ppi? ___" ___"
What will the physical dimensions of the image be if you print it at 600 ppi?
(i) 600  300 because 2"  300 dpi  1 pixel/dot = 600 pixels, and 1"  300 dpi  1 pixel/dot = 300 pixels
(ii) 2" x 1" because 600 pixels / 300 ppi = 2", and 300 pixels / 300 ppi = 1"
(iii) 1" x 0.5" because 600 pixels / 600 ppi = 1", and 300 pixels / 600 ppi = 0.5"
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28. © 2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.
Review Question
Suppose that you scan a 2"  1" picture in at a resolution of 300 dpi.
What are the pixel dimensions of the scanned image? ___ pixels  ___ pixels
What will the physical dimensions of the image be if you print it at 300 ppi? ___" ___"
What will the physical dimensions of the image be if you print it at 600 ppi?
What will the physical dimensions of the image be if you print it at 150 ppi?
(i) 600  300 because 2"  300 dpi  1 pixel/dot = 600 pixels, and 1"  300 dpi  1 pixel/dot = 300 pixels
(ii) 2" x 1" because 600 pixels / 300 ppi = 2", and 300 pixels / 300 ppi = 1"
(iii) 1" x 0.5" because 600 pixels / 600 ppi = 1", and 300 pixels / 600 ppi = 0.5"
(iv) 4"  2" because 600 pixels / 150 ppi = 4", and 300 pixels / 150 ppi = 2"
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29. © 2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.
Review Question
Suppose that you scan a 2"  1" picture in at a resolution of 300 dpi.
What are the pixel dimensions of the scanned image? ___ pixels  ___ pixels
What will the physical dimensions of the image be if you print it at 300 ppi? ___" ___"
What will the physical dimensions of the image be if you print it at 600 ppi?
What will the physical dimensions of the image be if you print it at 150 ppi?
True/False: You gain image detail and quality if you print the image at 600 ppi as noted in (iii).
(i) 600  300 because 2"  300 dpi  1 pixel/dot = 600 pixels, and 1"  300 dpi  1 pixel/dot = 300 pixels
(ii) 2" x 1" because 600 pixels / 300 ppi = 2", and 300 pixels / 300 ppi = 1"
(iii) 1" x 0.5" because 600 pixels / 600 ppi = 1", and 300 pixels / 600 ppi = 0.5"
(iv) 4"  2" because 600 pixels / 150 ppi = 4", and 300 pixels / 150 ppi = 2"
(v) False because it is the same image with the same number of pixels
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30. © 2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.
Review Question
Suppose that you scan a 2"  1" picture in at a resolution of 300 dpi.
What are the pixel dimensions of the scanned image? ___ pixels  ___ pixels
What will the physical dimensions of the image be if you print it at 300 ppi? ___" ___"
What will the physical dimensions of the image be if you print it at 600 ppi?
What will the physical dimensions of the image be if you print it at 150 ppi?
True/False: You gain image detail and quality if you print the image at 600 ppi as noted in (iii).
True/False: You lose image detail and quality if you print the image at 150 ppi as noted in (iv).
(i) 600  300 because 2"  300 dpi  1 pixel/dot = 600 pixels, and 1"  300 dpi  1 pixel/dot = 300 pixels
(ii) 2" x 1" because 600 pixels / 300 ppi = 2", and 300 pixels / 300 ppi = 1"
(iii) 1" x 0.5" because 600 pixels / 600 ppi = 1", and 300 pixels / 600 ppi = 0.5"
(iv) 4"  2" because 600 pixels / 150 ppi = 4", and 300 pixels / 150 ppi = 2"
(v) False because it is the same image with the same number of pixels
(vi) False because it is the same image with the same number of pixels
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