The basics of photograph scanning

Scared Cat Scanning would like to help you with any questions you have about scanning. If you can't find the answer to your question here then please ask us here Ask SCS. on the Scared Cat Scanning FAQ's page.

Scanners capture an image and convert it to a digital form that your computer can understand. Enabling the computer to be able to display, edit, store, or output images in any format. To use either for print, internet or just archival purposes.

The type of images that can be scanned is almost limitless. Anything from a photograph, a page of text, a drawing or illustration, or even a relatively flat 3D object like a coin, or a piece of fabric. Indeed many artists choose to scan their paintings rather than photographing it. In this way they keep the original colours of their artwork. (photographic processes by their very nature interpret the colours in their own way often adding a colour cast.) Scared Cat Scanning can offer very helpful advice on the subject of scanning originals.

Incorporate scans in design projects for newsletters, brochures, posters, direct mailers and any other printed material.

Scan printed text into your word processor and use an OCR (optical character Recognition) software to save retyping large quantities of text.

Scan images for your own personal use (family pictures, hobbies, clubs etc.) for e-mailing to your friends or creating a family album on your computer.

Although the technical operation of a scanner is complicated the principles behind scanning are not difficult to understand.
Your scanner is effectively a large light box with a moving light source. When you place an object on the scanner and close the lid, a light from the scanner is shined on the object. This light is then bounced back and captured by a strip of light-sensitive cells called a CCD (charge-coupled device).
The light sensitive CCD records the amount of light reflecting from each area of the object being scanned. Dark areas of the object reflect less light, and light areas reflect more. The CCD makes sense of all this and converts the reflected light waves into digital information.
Then the scanning software that controls the scanner reads this incoming digital info and reconstructs the whole image and you are left with an image as a file that your computer understands and can work with.

For quality results you need to be aware of the following. All of which can influence greatly the quality/degradation of the image.

Aside from these basic components, you can use scanner accessories
like the Transparent Media Adapter and the Auto Document Feeder to make
scanning even more effective.

Resolution defines the amount of detail stored by the scanner. It
can be measured in dots per inch or dpi or pixel per millimeter. The higher the dpi/ppm the more image information is stored. Image quality is enhanced with a higher resolution, but only up to a certain point, after which increasing resolution simply makes file sizes needlessly too large having no visible improvement in the image quality.
High-res scans also take significantly longer to print or transfer to other computers/media. Generally scans of up to 300 dpi are sufficient quality for most projects.
There's an important issue regarding resolution as it is often defined as interpolated and not optical. The difference being thus...
Optical resolution is the resolution of your scanners optics, if you like the physical or true resolution of your scanner.
Interpolated resolution is resolution increased by software. This software effectively adds information where there is none. Interpolated resolution can be useful for scanning line art or enlarging small originals, the image produced by this type of resolution is degraded and suffers from a lack of definition culminating in a visibly softer (un sharp) image.

Scanning at a higher resolution requires more time, memory, and disk
space. Its important to choose the best resolution for the particular job you have to do...There's really no point scanning at high res when you're intended use for the images is the Internet and vice-versa there's no point scanning at low res when you intend to use the images for print media.

An effective way to find the best resolution for your intended output is to know the lpi (lines per inch) of the output device or printer being used and then multiply it by 1.5 or 2.0.
Magazine printing presses generally use a screen frequency of 133 lines per inch, so multiply 133 x 1.5 or 2.0. Resulting in a scan at 199.5 dpi or 266 dpi. The optimal resolution setting for your image would then be 200 dpi to 266 dpi.

Lpi will vary, depending on the quality of the printing job. A newspaper uses approximately 85 lpi; magazines from 133 to 150; and fine art books may go as high as 200 to 300 lpi.
If you're outputting images to a monitor (such as doing multimedia work), you don't need to scan images higher than 72 dpi, as monitors are capable of only showing images up to 72 dpi. A higher-resolution image will not be any clearer on the monitor and will simply create larger files.

Remember that the higher the resolution, the larger your image file will be. For instance, an 8.5" x 11" color photograph scanned at 75 dpi takes up about 1.6 megabytes (MB). Doubling resolution to 150 dpi will increase the file size four times to approximately 6.3MB! Going to 300 dpi will increase file size to 26.2MB.

Therefore you need to select the lowest possible resolution that still gives you the required image quality and keeps the file sizes as small as possible.

High resolution is important if you're processing an image through a high-end color system that carries continuous tone data from the scanner through the final film output. This is because high resolution can improve the sharpness and clarity of the dots that make up the image. When to use interpolated resolution

Interpolated resolution is useful for scanning line art or enlarging small originals.

For line art: Set the resolution equal to that of your output device. For instance, if you're producing line art to be printed by a 1200-dpi imagesetter, you can interpolate resolution to up to 1200 dpi for superior results. This will produce smoother lines and eliminate some of the jaggedness characteristic of line art scans.

For enlarging small originals: Let's assume that you scan a 1" x 2" photograph at 300 dpi, and that your maximum optical resolution is 300 dpi too. To enlarge the image to two times the original size without loss of detail, interpolate the resolution to 600 dpi. This way, the image retains clarity and sharpness even if the print size was doubled.

Scaling is the process of creating larger or smaller images in your scanning software so that you need not resize the images later when they are delivered to your image-editing program.
Scaling has an inverse relation to resolution: The lower the resolution, the larger the image can be scaled. At the highest resolution, images can only be scaled smaller.

To illustrate the use of scaling, assume you scanned a 2" x 2" image at 300 dpi. To double image size to 4" x 4" without loss of detail, increase scaling to 200% and maintain resolution at 300 dpi.

This is the same as scanning the image at 600 dpi at 100% scaling and then using your image-editing software to enlarge the output.

Dynamic Range is the ability of the scanner to register a wide range of tonal values - something from near white to near black. A scanner with a good dynamic range is able to map input shades correctly to the output shades, so you will be able to see more detail in an image. On the other hand, a scanner with poor dynamic range won't be able to detect as wide a range of tonal values. In this case, the scanner will fill in the shadow areas or lose all detail in the highlight in an attempt to map the colors correctly. What emerges will be an image with less detail.

Color Calibration is the process of ensuring the accurate reproduction of color for images. Full color calibration is usually a two-step process: calibrating your input device, such as a scanner; and calibrating your output device, such as a printer or monitor. By calibrating your input and output devices correctly, color is captured accurately by your scanner and is reproduced faithfully on your monitor or output device.

Anything above a dynamic range of 2.0 is good, and anything above 3.0 is impressive.

The following is a guide to the most common features available on all image editing software. Using these features effectively will visibly improve on the scanned images quality.

This tool changes the brightness, contrast, and exposure of the entire image. Brightness determines the number of shades you get; contrast determines the intensity of those shades. An image with high contrast has less gray shades between black and white and appears to have less visible detail. An image with low contrast has more gray shades and tends to look flat.

This tool allows you to select a new shadow point to become the darkest value in an image, or to set a new highlight point to become the lightest value. The Shadow and Highlights tool can bring out more visible detail in an image, especially if it has only a limited range of grays or colors.

Curve

This tool lets you modify the gamma, which is the contrast affecting the middle range of grays in an image. The Curve tool lets you modify the midrange of grays without dramatically altering the shadows and highlights. Using a combination of the Shadows and Highlights tools together with the Curve tool gives you the most precise control for adjusting the tonal values of your images.

Filters

The Filters tool lets you apply or create special effects to your images. The filters include Blur, Blur More, Sharpen, Sharpen More, Edge, Enhancement, and Emboss.

The unsharp mask filter
A special mention for this filter as it invariably improves all images scanned and should be applied to varying degrees to every image scanned. This filter adds more contrast between adjoining colour areas.

Files
Scanned images are saved as files, and several file formats are available. Be aware of the advantage and disadvantages of each file format and how they are compatible with your image-editing software and printing method.

TIFF
Short for Tagged Image File Format. TIFF is probably the most popular file format. It's good for storing bitmaps in many different resolutions, color models and compression types, and is supported by many commercial applications. Use the TIFF format whenever possible, since this is the most widely used.

EPS
Short for Encapsulated PostScript. EPS is good for storing vector drawings but not for line art. EPS is ideal for print applications because it offers more control when printing to a PostScript printer.

PICT, PICT2
Short for PICT! is generally used for line art with limited color (usually 256 colors). PICT2 is for 8-bit grayscale or 24-bit color images.

GIF
Short for Graphic Image Format. A format used to store images with 256 colors or 256 shades of gray. Widely used on the internet for the convenience of the small file sizes generated because of it's limited colour capability.

JPEG
Short for Joint Photographers Expert Group. A compression algorithm used to store large color or grayscale files. Some versions of this compression format may result in minor degradation of image quality.

PCX
Developed by Z-soft for use in various paint programs. Also suitable for scanned images and is widely supported for PC use.

Scanned images vary in file size depending on several factors, including image type and resolution. As a rule, color images take up a bigger file size than grayscale or black-and-white images. And the higher the resolution in which the image is scanned, the bigger the resulting file size.

The following chart shows you the storage requirements for black-and-white images, grayscale images, and color images in different sizes and resolutions.

Single-bit Black and White

8-bit Grayscale

24-bit Color

36-bit Color

Paper Size	75 dpi	150 dpi	300 dpi	600 dpi	1200 dpi	2400 dpi
8.5" x 11"	2,311	9,245	36,980	147,920	591,680	2,366,719
8.5" x 5.5"	1,156	4,623	18,490	73,960	295,840	1,183,360
5" x 7"	865	3,461	13,843	55,371	221,485	885,938
4" x 5"	495	1,978	7,910	31,641	126,563	506,250
3" x 5"	371	1,484	5,993	23,731	94,922	379,688

Print Methods
Scanned images can be printed on a variety of devices. Below are a small selection of devices....

Black and white printers (laser, ink jet, dot matrix) are suitable for producing text and line art, but they're not as good for printing grayscale images. Use these printers to reproduce photographs for (For Position Only) purposes, for when you need to show a draft of how a document is laid out.

Ink jet and desk jet color printers can produce color or grayscale images that range in quality from coarse to medium. These printers can print 256 shades of color or gray, but colors don't register as well, and images usually end up slightly coarse or washed out. Use these printers for small quantities of color images or for proofs of images that will be printed later on a printing press.

Dye-sublimation color printers print images in photo-realistic color. Use these printers to print color images with continuous tone for small print jobs or for proofs of large printer jobs that will be done later on an imagesetter.

Printing presses can produce work of high quality. With these printers, your images need to be of sufficient resolution and saved in the file format the printer requires. Check with your printer/bureau.