You can scan any images provided they are flat and not too big. Usually images are in the form of colour transparencies, photographic prints, printed material or flat artwork.

Types of Scanner

Transparencies are scanned using transmissive scanners, whereas prints and flat artwork are scanned using reflective scanners.

In transmissive scanners, light passes through the transparent image, whereas in reflective scanners light is reflected off the surface of the image.

In both types, the varying intensities of light are usually converted into electrical charges by Charged-Coupled Device technology (CCD for short). These charges are then converted to digital data.

When using a scanner, ensure its optical resolution is adequate for the work you wish to do (See Scanning accurately). Resolution is described as either optical or optical supplemented by interpolated; interpolation is used to resample optically-recorded data during the scanning process.

Some scanners are described as having two optical resolutions, such as 300¥400 ppi (dpi). The lower figure represents the number of CCD elements across the scanner bed, the higher figure represents the number of recorded steps the CCD takes to pass down the length of the bed. In such cases, the lower figure, in this case 300, is often interpolated to match the higher figure, in this case 400. This gives a better result than an optical resolution of 300 in both directions.

Make sure you use a scanner which supports 24-bit or above. This will enable you to scan in full colour (recording over 16 million colours) as well as in grayscale and line.

Note: If you scan an image at 48-bit, you will need to reduce its depth to 24 within Photoshop 4.0 before you can use most of the program's commands. Do this by choosing 8 bits/Channel in the Mode sub-menu in the Image menu.

Note: Some desktop scanners are hybrid, combining both reflective and transmissive methods.

Scanning Controls and Terminology

Scanning controls and terminology can vary considerably from scanner to scanner. You will find some controls are fairly intuitive; others not very logically laid out. It may take you time to familiarise yourself with the main controls on your scanner but it is time well spent if you wish to work efficiently.

Terminology can present a problem as manufacturers use different words to describe the same things, especially the level of colour in images. This attribute can be variously described as:

• 1-bit; line; bitmap: black and white
• 8-bit; grayscale: black and white photo
• 24-bit; colour: millions of colours
• 32-bit and 48-bit; colour: billions of colours

1-bit refers to images that contain only black and white areas.

8-bit refers to images that contain 256 shades of grey, including black and white.

24-bit refers to images, which contain over 16.7 million colours.

Both 32-bit and 48-bit refer to images, which contain billions of colours.

The terms line, black and white photo and colour are also used to describe the quality of originals.

Scanning from within Photoshop

Most scanners come with versions of their software drivers in the form of Photoshop-compatible plug-ins. Some come with generic TWAINdrivers. Either system allows you to load and access scanning controls from within Photoshop itself. This is the best way to scan: it is seamless, with scanned images automatically converted into Photoshop documents.

You can, if you wish, scan an image independently of Photoshop by loading the scanning program directly. If you do this the final scanned image will need to be saved in TIFF format, uncompressed and then closed. You can then re-open the image within Photoshop for further processing. See Opening an existing image.

There is no qualitative difference between the two approaches; the former approach is just quicker and more convenient.

Note: Plug-ins and TWAIN drivers need to be placed in the Import/Export folder within Photoshop's Plug-ins folder. The Plug-ins folder needs to be selected within the Plug-ins and Scratch Disks Preferences dialogue box for the appropriate command to be listed in the Import or Acquire sub-menu.

Scanning Attributes

The scanning process involves setting certain image attributes, whatever the make of your scanner. These attributes define the dimensions, level of colour (bit-depth) and density of data in the final image.

These can be listed as:

• Crop (area of the original to be scanned)
• Dimensions (final dimensions of scanned image)
• Bit-depth (whether line, grayscale or colour information is to be recorded)
• Resolution (density of data recorded in scanned image)

The Scanning Process

The features referred to in the following process may differ from your scanning controls. Refer to the user manual, which came with your scanner for operational instructions specific to your machine.

Ensure that your scanning program is set to its default calibration unless it has been professionally re-calibrated.

Brightness, gamma and colour settings should be neutral and any sharpening control should be disabled.

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