Digital Photography
Created by Joel May November 2007
revised January, 2009
Part IV - Other Ways to Create or Capture Digital Images
- In addition to capturing them with a digital camera, digital images can also be captured from:
- Scanners
- E-Mail Messages
- Web Sites
- Film Cameras
- Types of Digital Scanners
- Flatbed – easy to use for digitizing text documents (OCR- Optical Character Recognition), color or black-and-white images, flat artwork transparencies and even scan three-dimensional objects. May include film or transparency adapters.
- Sheetfed – take up very little room. Not as versatile as flatbed. Good as transportable.
- Photo – for prints up to 11X17 inches and more expensive ($250+)
- Transparency – for scanning photographic slides. It transmits light through slides from above.
- Obtaining Images from a Scanner
- There are typically three ways to obtain an image from a scanner
- Use the software that came with the scanner
- Use the buttons on the scanner itself
- Use the "Import" function available in all photo-editing and photo-cataloging software. The is called TWAIN
- How does a scanner work?
- A moving light source reflects off the object being scanned
- Prisms and mirrors direct the light through a series of filters
- Some scanners scan the object three times (once each for red, green and blue).
- Others scan once but separate the results into three separate images
- The information is sent to a Charge Coupled Device (CCD), an array of light sensitive diodes
- The sensitivity of the CCD is measured in dots per inch (dpi)
- The more dpi, the more detail there will be in the finished picture
- The varying levels of each of three separate colors (red, green and blue) are converted to numeric values. The resulting digitized information is known as a Raster Image
- The raster image is sent to the computer to the computer for manipulation and storage
- Scanning Transparencies (Slides)
- The light source must be in the lid of scanner
- The light shines down through the transparency on to the Charge Coupled Device (CCD)
- See 2.a. above and the items following
- Scanner Specifications
- Resolution – Measured in DPI (Dots Per Inch) Most scanners have at least 300x300
- The scanner's DPI is determined by the number of sensors in a single row (x-direction sampling rate) of the CCD array multiplied by the precision of the stepper motor (y-direction sampling rate).
- E.g. A scanner with a 300x300 resolution and the capability to scan a standard sheet of letter paper (8˝ x 11 inches) would have 300 x 8˝ = 2,550 sensors in each row (A single-pass scanner would have three times as many or 7,650)
- True vs. Interpolated DPI
- Example: Scanner specs report resolutions of 600x1200 and 9600x9600 DPI
- 600 is the true resolution and 9600 the interpolated resolution
- Always look for the smaller number when comparing scanners
- Color Bit-depth - amount of information scanner can record per pixel.
- You need at least 8 bits for each of three primary scanning colors -- red, green and blue -- which gives you a total of 24 bits per pixel (8 + 8 + 8 = 24). This is capable of sensing 16.7 million colors (2 to 24th power). OK for screen viewing.
- Better scanners have 30, 36, 42, or 46 bit color depth – higher is better for high quality printing
- Dynamic Range – the scanner's ability to record different tonal qualities
- Examples: 2.4 – typical of low cost scanners (usually not stated); 2.8-3.2 - mid-range scanners; 3.3 and over – high end (typical for film scanners)
- Software Included With Scanner
- All will come with a software driver which should be installed before the scanner is connected to the computer
- This will be the "control console" which you use to send commands to the scanner
- All have basic image adjustment (Rotate & crop image, adjust brightness, contrast, and color balance)
- Most will have Optical Character Recognition (OCR) software for scanning in text to be edited
- Some Scanning Tips
- When scanning an image for printing in its original size, match your scanning DPI to your printer (150-300 DPI)
- When scanning to print an enlargement, use this formula: Scan resolution = Printer DPI X (Final Image Width/Original Image Width). So, for example, if you want an 8x10 image from a 4x6 original and your printer has a DPI of 300, your scan resolution would be 300x(8/4)=600
- When scanning for e-mail or for Web posting, scan at 75 DPI
- Finding Scanner information on the Web
- Obtaining Images from the Web or Email
- It's a simple Four-Step Process
- Right-Click on the Image
- Choose “Save Picture As” from the menu
- Decide where to save the image and what to name it
- Click OK
- It’s Yours!!
- Digital Image Search Engines can find images for you both on the Web generally but also in Web photo galleries. Here are some examples, courtesy of Fagan Finder
- Digital Images from a Film Camera
- Most film processors will provide digital versions when they develop your photographs
- You can then treat the images just as you would images from a web site, scanner or digital camera
- The most important advantages of this approach are:
- You don’t have to buy any new equipment
- You get far more camera for your money
- You don’t have to face the delayed shutter problem
- The most important disadvantages of this approach are:
- You can’t view, edit or delete your images on the fly
- You still have to buy film
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