"Digital Media Primer" Yue-Ling Wong, Copyright (c)2013 by Pearson Education, Inc. All rights reserved.

Chapter 3 Capturing and Editing Digital Images Part 1 Digitizing Images by Scanning

Types of Scanners Flatbed Sheet-fed Handheld Drum

Scanner Resolution Optical resolution Enhanced resolution Reported in dpi (dots per inch)

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.

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.

Dot vs. Pixel Generally speaking, a dot (sensor) produces a sample (pixel). But a dot is not a pixel.

A scan head only have one row of sensor A scan head only have one row of sensor. So how can it produce color values for a whole picture?

Here is how Get a row of color values Move the scan head forward a little bit Get another row of color values .

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

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

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)

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.

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

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.

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.

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

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

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"

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"

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"

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

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