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Input – Principles of Scanning

Posted in Lecture Materials by Paul Turounet on May 9, 2009

Scanners

Epson V700 Flatbed Scanner (top left); Nikon Super Coolscan 5000 35mm Film Scanner (top right); Nikon Super Coolscan 9000 35mm and medium-format Film Scanner (bottom left); and Hasselblad Flextight X5 multi-format (35mm up to 4″ x 5″) Drum Scanner

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In order to bring analog information into the digital environment, it is necessary to utilize a scanner. There are various scanners, including drum scanners, flatbed scanners and CCD film scanners that can be utilized to convert a negative, transparency, or reflective material into a digital image file. Whether the photographic images being scanned are black & white negatives, color negatives, color transparencies or prints, each of these media is primarily optimized for the photographic process and not for digital scanning. Therefore, the task of creating an optimum digital file from these various possibilities is dependent on the quality of the original media, the quality of the scanning hardware as well as the how the scanner software and interface are utilized.

Before deciding what type you would use, it is important to determine how the scanned image and subsequent file would be utilized. The three most widely used scanners include drum scanners; flatbed scanners and CCD film scanners. High-end drum scanners are considered to produce the highest quality and are used primarily by professional service bureaus and photographic labs due to their high cost. Flatbed scanners work similar to a photocopy machine. The professional ranges of flatbeds are capable of scanning not only reflective materials, but also negatives and transparencies with the transparency hood. CCD film scanners are designed specifically to scan film emulsions at high resolutions from 35mm format to 120 formats.

As suggested earlier, it is important to start with a high quality original, as this will determine the quality of the scan.  Other considerations that will contribute to the quality of the scan include how the scanner software and interface are utilized.  The resolution, dynamic range and bit depth capabilities of the scanner are important considerations in creating high quality scans.

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Resolution

The resolution of a scanner determines the level of detail recorded by the scanner and is often expressed and measured as dots per inch (dpi).  However, the resolution of the scanner is specified by pixels per inch (ppi) and indicates how precisely the scanner can resolve an image.

Basically, there are two types of resolution.  The “optical” resolution is the “native” resolution of the scanner as determined by the optics of the scanner hardware.  On the other hand, interpolated resolution is resolution enhanced through software, which adds or subtract pixels in a digital image file.

Image quality improves with higher resolutions, but only up to a certain point, after which increasing resolution simply makes file sizes unmanageable without yielding any visible improvements to the image.  In determining resolution, the final outcome and use will dictate the number of pixels per inch (ppi – input) to the final resolution of dots per inch (dpi – output).  If the final output of the file is to be used strictly on a computer monitor, 72 to 96 dpi (monitor) is desired as this is the maximum on monitor displays.  If the final output of the file is to be printed, such as a digital photographic print, 300 dpi (print) is desired.

An easy way to determine the best resolution is to set the resolution to the maximum optical resolution of the scanner (at 100%).  Alternatively, set the resolution to create a file of the maximum desired size at the resolution of the final output device while not exceeding the optical resolution of the scanner.  This avoids upsampling and interpolating resolution.  If smaller versions of the scan are desired, they can be downsized from this master file.

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Dynamic Range

The dynamic range is a measure of the scanner’s ability to record the range of tonal values in the original.  Typical dynamic ranges of a scanner run from 3.0 to 4.2 and the higher the number, the more sensitive the scanner is to attain a greater tonal range and record detail from the brightest highlights to the darkest shadow areas.

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Bit Depth

The bit depth of an image is a mathematical description of the maximum levels of tone that are possible, expressed as a power of 2.  The more levels the scanner is capable of capturing at the scanner stage, the more flexibility is possible when optimizing the file.  For example, an 8-bit grayscale image is made up of 256 tones of gray.  An RGB color image is made up of three-color channels.  Each channel contains 8-bit grayscale information defining the amount of each color component of the full color image, making it a 24-bit color that can define up to 16.7 million possible colors.  Utilizing higher bit depths (greater than 8-bits per channel/24 bit) will provide greater detail and smoother tonal gradations.

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Image Size, File Size and Output Size

The image size, file size and output size are determined by the number of pixels the image contains.  The pixel dimensions are the surest way of defining the size of a digital file.  This can be expressed by the following formula:  number of pixels = physical dimension x (ppi) resolution.

In other words, there is a reciprocal relationship between pixel size, the physical dimensions and resolution.  For example, if a digital image has 3000 pixels along one axis, then the pixels could be output at 10 inches at a resolution of 300 ppi.

Altering the image size dimensions and resolution can be adjusted using the Image Size dialog as well as with the Crop and Rectangular Marquee tools.  In addition, the Resize Image Assistant, located in the Help menu, can be used as a guide in resizing images.

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Image Resampling

Image resampling (adding or subtracting pixels from the file) is also known as interpolation.  While resampling down will not deteriorate a digital image file quality, “interpolating up” will describe the pixels with less definition that are soft.  Within Photoshop, there are five methods when assigning values for new pixels generated:

Nearest Neighbor is the simplest interpolation as it assigns values for new pixels based pixels near each other.

Bilinear Interpolation calculates pixels by reading horizontal and vertical neighboring pixels.

Bicubic Interpolation
provides better image quality by reading values horizontally, vertically, and diagonally to calculate a new pixel value.

Bicubic Smoother is considered the ideal choice for making an image larger.

Bicubic Sharper is beneficial when the pixel resolution is reduced, retaining more detail and sharpness.

Instructions for Using the Epson V700 Flatbed Scanner Epson

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  • Open cover of flatbed scanner and place reflective material face-down on scanner bed and close top or carefully remove accessory for scanning negatives/transparencies and place File Saver Page | Film Adapter with negatives/transparencies face-down (base-side up) on scanner bed and close top.
  • Open Adobe Photoshop. Go to File, Scroll down to Import and click on appropriate scanner.
  • Set scanner settings in dialog box as follows:

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EpsonSettings

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  • Click Preview.
  • Crop as necessary and click Scan.
  • Save as PSD format.

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Instructions for Using the Nikon Film Scanners   Nikon

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  • Turn on Nikon Film Scanner and insert negative/slide into appropriate negative/slide adapter.  The base side of the film needs to be face-up.
  • Open Nikon Scan Software. Two windows will appear – Operation Window and a Tool Palette.
  • Set scanner settings in operations window as follows:

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NikonSettings

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  • Click on the Thumbnail Tab which will display thumbnails of each image from the strip of film being scanned.
  • Select the image to be scanned, click on the Thumbnail and then click the Preview.
  • With the Preview Image located in the Operation Window, proceed to the Tool Palette to determine Image Settings.
  • Click on Digital Ice box for automated retouching functions only if color film is being scanned.
  • Click Scan.  Eject the film strip by clicking the Eject Film Button in the top left corner of the Operations Window.
  • Save as TIFF format and close file on desktop.  Reopen in Adobe Photoshop and Save As PSD file.

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Technical Assignment and Requirements

Using the Nikon Film Scanner:

  • Scan one frame from a strip of negatives that was originally printed in the darkroom.
  • Optimize in Adobe Photoshop and make a grayscale digital photographic inkjet print.

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