The Scanning Process

General Frame Densitometer

General Frame Densitometer

Image Type: Standard

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FIGURE 77 Optimal Flatbed Scanning.

In Figure 77 my intention is to make an 11.4 x 17 inch ink jet print of this image, but we will use this scanning illustration to learn what's involved with creating optimal scans for a variety of different uses.

1. Bit Depth. Notice that I have set the bit depth to "48 Bit Color."

Note: The number 48 means that each of the three color channels — Red, Green, and Blue — will contain 16 bits of visual information. 16 x 3 = 48. More on this later.

This setting will create a digital file with the highest bit depth possible with this scanner. As you will learn later in the section Bit Depth and Digital Exposure, having the maximum number of pixel levels will allow me to edit the contrast of this image without compromising the quality of the resulting print.

When you shoot your work in the camera raw format you're also creating high bit depth images that maximize the number of pixel levels in our image.

2. Output Size. It is essential that you set the Output setting to the largest size print you ever intend to make. It's always possible to downsample your digital image file to a smaller size without losing quality but scaling it up through interpolation will degrade the image.

3. Resolution. Scanners often display their resolution settings in terms of dots per inch (dpi). This is in recognition of the fact that nothing is more important than sending an ideal digital file to your printer!

• Optimal Resolution for Ink Jet Prints. The minimum resolution you should consider for fine digital prints is 240 dpi. The standard scanner resolution setting for digital prints at 300 dpi, although some say that 360 dpi is ideal.

• Optimal Resolution for the Web. If the only place you plan to display your image is on a computer monitor, for example, if your image will only appear in a web browser, there is no reason to scan at a resolution higher than 72 dpi, the fixed pixel size of computer monitors.

• Optimal Resolution for the Print World. The major stock agencies are setting the standards for professional scans intended for A3 or double page spread printing. The scanning resolution they require for this is 600 dpi.

Just as important, these companies are requiring incoming images that they represent to have a minimum file size, 30 megabytes for one example, and that these images only have 8 bits per channel and not be interpolated.

The meaning of the words "8 bits per channel" will be discussed very shortly.

To meet this requirement, digital stock photographers are using digital cameras with at least 11 megapixel sensors, shooting in raw format if they intend to edit the images, and then reducing the image's bit depth to the 8 bit per channel minimum standard. This is in recognition of the fact that although it's important to scan or capture your images at the highest resolution possible if you intend to edit them in Adobe Photoshop, there is no quality advantage to sending more than 8 bits per channel of information to ink jet or offset printers.

4. File Size. Notice that the settings I've chosen for this scan will result in a file that is just over 100 megabytes in size. Ultimately this is the most important number in the box!

Pioneering child psychologist, Jean Piaget, is famous for creating a test of cognitive development that uses two cubes of clay that are exactly the same size. Most children will readily say that they are the same. But, if you then flatten one cube until it covers a wide area, children below a certain level of development will claim that the cube contains less clay. A similar principle applies to the world of digital photography.

The quality of an image you create is always determined by the combination of the image's resolution, bit depth, and pixel dimensions; in other words, the total amount of visual information you have captured or scanned, not any one of these individually.

The following is an example of how this works. For the image in Figure 77, my goal was to create a fine ink jet print that was 11.4 x 17 inches high. Figure 78(a) is the Image Size box for this scan.

Image Size — Pixel Dimensions: 99.8M {was 235.2K)

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