ITEC2110, Digital Media Chapter 3 Digital Image Processing 1 GGC -- ITEC Digital Media

 Capturing Images  Digital Image Retouching  Color Adjustment  Selection Tools and Layer Basics  Output Images  Editing Vector Graphics Content 2

 Flatbed  Sheet-fed  Handheld  Drum Types of Scanners 3

 Optical resolution (hardware dependent)  Enhanced resolution (software dependent)  Reported in dpi (dots per inch) Scanner Resolution 4

To see what "dots" in dpi stands for, let's look at how scanners work. 5

 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. How Scanners Work 6

 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 7

A scan head only have one row of sensor. So how can it produce color values for a whole picture? 8

 Get a row of color values  Move the scan head forward a little bit  Get another row of color values  Move the scan head forward a little bit . Here is how 9

 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 Sampling 10

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 11

Basic steps: 1.Determine the pixel dimensions of the final image 2.Determine the scanning resolution – (pixel dimensions from step 1) / (physical dimensions of your picture) Determining Scanning Resolution 12

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" = 160 dpi Scanning resolution based on the height = 525 pixels / 4 " = 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 = 800 pixels 4"  160 dpi = 640 pixels If you want exactly 800  525 pixels, you will need to crop/scale the final image. Determining Scanning Resolution for Web or On-screen Display Example 13

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" = 780 dpi Scanning resolution based on the height = 3000 pixels / 4 " = 750 dpi We will pick the highest dpi of the two, i.e., 780 dpi. With 780 dpi, your final image will have the pixel dimensions: 5"  780 dpi = 3900 pixels 4"  780 dpi = 3120 pixels Determining Scanning Resolution for Print Example 14

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/scale the final image. Determining Scanning Resolution for Print Example 15

 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. Tonal Adjustments During Scanning 16

 point-and-shoot  D-SLR (digital single-lens reflex)  Most D-SLR cameras use interchangeable-lenses Digital Cameras 17

 Types  CCD (charge coupled device)  CMOS (complementary metal-oxide semiconductor)  The size of the sensor and the number of light-sensing sites determine the maximum resolution of the digital camera. Digital Camera Sensors 18

Megapixels 1 megapixel = 1,000,000 pixels 19

An image of 3000  2000 pixels has a total number of pixels of: 3000  2000 pixels = 6,000,000 pixels = 6,000,000 pixels/1,000,000 pixels/megapixel = 6 megapixels Megapixels Example 20

 Give an approximate number of total pixels in an image  Does not provide information about the aspect ratio (i.e., relative width and height) of the image Megapixels 21

 No  Digital photo quality is determined by:  the optics of the lens  the size and quality of the sensor  the camera electronics  the camera’s image processing software Does a digital camera with more megapixels mean better image quality? 22

 The print size depends on the printing resolution.  Let's return to our megapixel examples:  6-megapixel image: 3000  2000 pixels  2-megapixel image: 1600  1200 pixels Does a digital camera with a higher megapixel rating give bigger prints? 23

 Printed at 150 ppi: 3000 pixels / 150 ppi = 20" 2000 pixels / 150 ppi = 13.3"  Printed at 300 ppi: 3000 pixels / 300 ppi = 10" 2000 pixels / 300 ppi = 6.7"  Printed at 600 ppi: 3000 pixels / 600 ppi = 5" 2000 pixels / 600 ppi = 3.3" Print Sizes of a 6-megapixel Image 24

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. Review Question 25

Suppose that you scan a 2"  1" picture in at a resolution of 300 dpi. i.What are the pixel dimensions of the scanned image? ___ pixels  ___ pixels Review Question 26

Suppose that you scan a 2"  1" picture in at a resolution of 300 dpi. i.What are the pixel dimensions of the scanned image? ___ pixels  ___ pixels ii.What will the physical dimensions of the image be if you print it at 300 ppi? ___"  ___" Review Question 27

Suppose that you scan a 2"  1" picture in at a resolution of 300 dpi. i.What are the pixel dimensions of the scanned image? ___ pixels  ___ pixels ii.What will the physical dimensions of the image be if you print it at 300 ppi? ___"  ___" iii.What will the physical dimensions of the image be if you print it at 600 ppi? Review Question 28

Suppose that you scan a 2"  1" picture in at a resolution of 300 dpi. i.What are the pixel dimensions of the scanned image? ___ pixels  ___ pixels ii.What will the physical dimensions of the image be if you print it at 300 ppi? ___"  ___" iii.What will the physical dimensions of the image be if you print it at 600 ppi? iv.What will the physical dimensions of the image be if you print it at 150 ppi? Review Question 29

Suppose that you scan a 2"  1" picture in at a resolution of 300 dpi. i.What are the pixel dimensions of the scanned image? ___ pixels  ___ pixels ii.What will the physical dimensions of the image be if you print it at 300 ppi? ___"  ___" iii.What will the physical dimensions of the image be if you print it at 600 ppi? iv.What will the physical dimensions of the image be if you print it at 150 ppi? v.True/False: You gain image detail and quality if you print the image at 600 ppi as noted in (iii). Review Question 30

Suppose that you scan a 2"  1" picture in at a resolution of 300 dpi. i.What are the pixel dimensions of the scanned image? ___ pixels  ___ pixels ii.What will the physical dimensions of the image be if you print it at 300 ppi? ___"  ___" iii.What will the physical dimensions of the image be if you print it at 600 ppi? iv.What will the physical dimensions of the image be if you print it at 150 ppi? v.True/False: You gain image detail and quality if you print the image at 600 ppi as noted in (iii). vi.True/False: You lose image detail and quality if you print the image at 150 ppi as noted in (iv). Review Question 31

Name two methods you can capture digital images. Review Question 32

1 megapixel = ___ pixels Review Question 33

An image of 6000  6000 pixels is said to have ___ megapixels. Review Question 34

Does a digital camera with more megapixels always mean better image quality? Review Question 35

What are the factors of digital cameras that determine the image quality? Review Question 36

Does a digital camera with a higher megapixel rating give bigger prints? Review Question 37