Digital Media Daniel Fuller ITEC 2110
Scanners
Types of Scanners Flatbed Sheet-fed Handheld Drum
Scanner Resolution Reported in dpi (dots per inch) To see what "dots" in dpi stands for, let's look at how scanners work
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 can only have one row of sensors So how can it produce color values for a whole picture?
Here is how Capture a row of color values Move scan head forward a little bit Get another row of color values Move scan head forward again Etc.
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
16 Sensors Across Scanned 22 Rows
Determining Scanning Resolution
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: 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 Scan Resolution: Web or Onscreen Display
Determining Scan Resolution: Web or Onscreen Display Suppose: The monitor resolution of your target audience is 1600 1050 pixels You want the image to appear halfway from the width and height of the screen The original picture is 5" 4"
Determining Scan Resolution: Web or Onscreen Display Suppose: The monitor resolution of your target audience is 1600 1050 pixels You want the image to appear halfway from the width and height of the screen Step 1. The pixel dimensions of your final image: 1600 x 1050 / 2 = 800 525 pixels
Determining Scan Resolution: Web or Onscreen Display Suppose: The original picture is 5" 4 The pixel dimensions of your final image = 800 525 pixels Step 2. Scan resolution based on width = 800 pixels / 5" 1 dot/pixel = 160 dpi Scan resolution based on height = 525 pixels / 4 " 1 dot/pixel = 131 dpi We will pick the highest dpi of the two, i.e., 160 dpi
Determining Scan Resolution: Web or Onscreen Display Suppose: You are scanning the image at 160 dpi Step 3. 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 Note that this isn t quite what we originally wanted. If you want exactly 800 525 pixels, you will need to crop the final image.
Determining Scan Resolution: Print
Determining Scan Resolution for Print Suppose: Your original picture is 5" 4" You want to scan the picture to print at 13" 10" at 300 ppi
Determining Scan Resolution for Print Suppose: You want to scan the picture to print at 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
Determining Scan Resolution for Print Suppose: Your original picture is 5" 4 The pixel dimensions of your final image should be 3900 pixels x 3000 pixels Step 2. Scan resolution based on the width = 3900 pixels / 5" 1 dot/pixel = 780 dpi Scan 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.
Determining Scan Resolution for Print Suppose: You are scanning the image at 780 dpi Step 3. 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 Scan Resolution for Print Thus, the final image 3900 3120 pixels will be printed in these physical dimensions: 3900 pixels / 300 ppi = 13" 3120 pixels / 300 ppi = 10.4" = 13 x 10.4 Note that this isn t quite what we originally wanted. If you want exactly 13" 10", you will need to crop the final image.
Tonal Adjustments
Tonal Adjustments During Scanning If your scanner has the option, be sure to maximize tonal range during scanning Be careful, because any tonal ranges cropped off during scanning will not be recovered after scanning
GOOD: Tonal Range Maximized During Scanning histogram use maximized tonal range
BAD: Use Narrow Tonal Range During Scanning histogram use narrow tonal range Missing very dark and very bright tones. Looks dull and low in contrast.
BAD: Crop off Highlights During Scanning histogram crop off highlights The brightest areas all become white.
Digital Photography
Digital Cameras Point-and-shoot D-SLR (digital single-lens reflex) Most D-SLR cameras use interchangeablelenses
Digital Camera Sensors 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.
Megapixels 1 megapixel = 1,000,000 pixels
Megapixels 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 Example An image of 3000 2000 pixels has a total pixel count of: 3000 2000 pixels = 6,000,000 pixels = 6,000,000 pixels/1,000,000 pixels/megapixel = 6 megapixels
Megapixels Example An image of 1600 1200 pixels has a total number of pixels of: 1600 1200 pixels = 1,920,000 pixels = 1,920,000 pixels/1,000,000 pixels/megapixel = 1.92 megapixels rounded up to 2 megapixels
Megapixels Example An image of 1800 1100 pixels has a total number of pixels of: 1800 1100 pixels = 1,980,000 pixels = 1,980,000 pixels/1,000,000 pixels/megapixel = 1.98 megapixels rounded up to 2 megapixels
Does a digital camera with more megapixels mean better image quality? No Digital photo quality is determined by: Optics of the lens Size and quality of the sensor Camera electronics Camera s image processing software
Does a digital camera with a higher megapixel rating give bigger prints? 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
Print Sizes of a 6-megapixel Image 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 2-megapixel Image Printed at 150 ppi: 1600 pixels / 150 ppi = 10.7" 1200 pixels / 150 ppi = 8" Printed at 300 ppi: 1600 pixels / 300 ppi = 5.3" 1200 pixels / 300 ppi = 4" Printed at 600 ppi: 1600 pixels / 600 ppi = 2.7" 1200 pixels / 600 ppi = 2"
Does a digital camera with a higher megapixel rating give bigger prints? As you see in the examples: With the same printing resolution, yes, images with more megapixels give bigger prints. With different printing resolutions, the 2- megapixel image (printed at 150 ppi) gives a bigger print than the 6-megapixel image (printed at 300 ppi).
Printing Images
Print Size of an Image Print Dimensions (in inches) = Pixel Dimensions (in pixels) Pixel Resolution (in ppi) Both the pixel dimensions of an image and the image resolution (ppi) affect the image s print size
Print Size of an Image Both the pixel dimensions of an image and the image resolution (ppi) affect the image s print size What this means that you can't determine the print size if you: Only know the pixel dimensions of an image without the print resolution (ppi) Only know the print resolution (ppi) without the pixel dimensions of an image
Scenario 1: Maintaining the Print Dimensions To make an 8" x 4.5" print Print Resolution (ppi) Required Pixel Dimensions 100 ppi width = 8" 100 ppi = 800 pixels height = 4.5" 100 ppi = 450 pixels 200 ppi width = 8" 200 ppi = 1600 pixels height = 4.5" 200 ppi = 900 pixels 300 ppi width = 8" 300 ppi = 2400 pixels height = 4.5" 300 ppi = 1350 pixels With a fixed print size, you need larger pixel dimensions with a higher print ppi.
Scenario 2: Maintaining the Pixel Dimensions For an image of 1600 x 900 pixels Print Resolution (ppi) Resulted Print Size 100 ppi width = 1600 pixels / 100 ppi = 16" height = 900 pixels / 100 ppi = 9" 200 ppi width = 1600 pixels / 200 ppi = 8" height = 900 pixels / 200 ppi = 4.5" 300 ppi width = 1600 pixels / 300 ppi = 5.3" height = 900 pixels / 300 ppi = 3" With fixed pixel dimensions, you get a smaller print with a higher print ppi.
Scenario 3: Maintaining the Print PPI The print resolution is kept at 300 ppi Print Size Required Pixel Dimensions 5.3" 3" width = 5.3" 300 ppi = 1600 pixels height = 3" 300 ppi = 900 pixels 8" 4.5" width = 8" 300 ppi = 2400 pixels height = 4.5" 300 ppi = 1350 pixels 16" 9" width = 16" 300 ppi = 4800 pixels height = 9" 300 ppi = 2700 pixels With a fixed print ppi, you need larger pixel dimensions for a larger print.
In GIMP: Image > Print Size Print Dimensions PPI
In GIMP: Image > Scale Image Image Dimensions PPI
Effect of Scaling an Image on Image Quality Scaling an image usually deteriorates the image quality somewhat. Scale down: You are removing pixels, i.e., the image will lose some details. Scale up: Interpolation will be perform to fill in extra pixels. The resulted image will appear blurry.
Print Resolution PPI vs. Printer Resolution DPI Print Resolution PPI Printer Resolution DPI
Printer Resolution DPI Number of ink dots per inch Color inkjet printers produce a microscopic spray of ink which appears to be very tiny dots of ink. These ink dots of different colors--but a limited number of colors--produce the required color by optical mixing. The color of a single pixel of an image is represented by a group of printer dots.
Print PPI vs. Printer DPI Effect on print size Effect on image quality Increasing Print PPI Depending on the scenario, the print size may decrease or maintain the same. No Increasing Printer DPI No The color appears smoother on the print. However, higher dpi uses more ink and requires longer time to complete the print job
Questions?