|Jean LeLoup & Bob Ponterio
In today's world of digital cameras, phones and Google images, teachers have less and less need of photo scanners. Sometimes, however, the ability to scan an image in order to include it in a presentation using authentic materials can be quite useful. This can allow you to prepare an online lesson using a digitized image from a magazine, a printed photograph, a flyer, packaging from products sold where the target language is spoken, etc.
Scanning a photo on a flatbed scanner involves a number of basic steps
that are essentially the same no matter what particular scanner and
are used. As light is shone on the photo, photoelectric cells
the red, green,
and blue light (RGB)
from individual points of the image. Each point is a pixel (picture element), and the resolution of the image is measured in
per inch. The total number of pixels in a rectangular digital image can
found by multiplying the horizontal width in pixels by the vertical
in pixels. So an image that is 600x800 has 600 dots along one side and 800 dots along another. If it was scanned at 120 dpi, that means that one inch running along the original photo was converted to 120 dots in the scanned image (or 14,400 dots in a square inch).
Every pixel in a color image can be represented by three
indicating the brightness of the red, green,
and blue components of the
color, and in fact, each pixel on a computer screen (or your TV - whether CRT, LCD or plasma) is made of three
dots, one red, one green, one blue. Our eye then interprets various combinations of these
three dots as the millions of colors that we perceive. The way colors are mixed to fool our
into seeing nuances of color or perceiving a higher resolution than is
present can be mathematically quite complex, but it is not essential to understand Floyd-Steinberg Diffusion Dithering and other
complexities to use them.
Different image formats store information about pixels and colors in
ways. A GIF image, for example, can use a maximum of 256
colors stored in an indexed color table. A JPG image uses 256
possible values for each of the three color elements (RGB) for a total
of 256x256x256 = 16,777,216 different possible colors for each
You may have seen colors represented in hexadecimal (base 16) FF080A = 255 red, 8 green, 10 blue. Image files take up large amounts of memory without some form of
GIF uses a compression scheme that works well for small numbers of
without smooth transitions, but GIF compression causes no loss of image
quality. JPG allows the user to determine the degree of
of the image, but although it can greatly compress a large number of
and can handle smooth transitions, JPG compression is lossy (the more
image is compressed, the more information / quality is lost).
Indeed, any time an image is converted from one format or size to another, some information is likely to be lost.
The quality of an image will depend on the resolution (the number
pixels used), the color depth (the number of possible color values for
each pixel), the effectiveness with which the colors are used to
the range of brightness and contrast in the picture, and any loss of
caused by the compression of the image. For these reasons, the two keys to successful scanning are to scan the image at the largest resolution (size) that you will need and to capture with a brightness and contrast that look best to your eye.
HP ScanJet 5p
One example is the HP ScanJet 5p scanner. You may be able to launch it from the File / Import menu in Photoshop, Paint Shop Pro,
GIMP, or any other image editor. Or you might have to launch the software separately.
First check that the software is set for color pictures, then
click Scan to get a preview image.
||The marquee tool will let us draw a rectangle to select the
the final scan. The Options menu is needed to set the resolution
(image size) of the output. For a color photo that you wish to display on a
screen, the settings for reflective material, millions of colors, 72
should work well, though the best resolution will depend on the size of the final image you need.
After the options have been set, clicking Accept will
||The ruler icon will allow us to change the resolution of the
image before completing the scanning process.
HP ScanJet 3500c
Here is another example. Much like the
File / Import to find the scanner.
The get a preview image, use the mouse and cursor to select the
scanning area, then accept this
to begin the scan.
In all cases, the key is to pay careful attention where you save
scanned image (in which folder) so you do not misplace it.
The most common adjustments are:
- Brightness/Contrast/Exposure time - Increasing
to decrease contrast so if you change one, you may need to adjust the
also. This can work if the overall brightness is not quite right, not when
a part of the image needs adjustment.
- Levels (Shadow & Highlight) - This tool works best when
too dark or light areas are too light or when adjustments can be spread
out broadly in the light or dark bands. Your objective, as when
a photograph, is to make the best use of the contrast range of the
by using all the colors from full black to full white. Look at
histogram (a graphic representation of brightness distributions), move
the black and white triangles to identify darkest and lightest colors,
move the gray triangle to spread out mid-tones.
- Curve tool - This tool works well for bringing out
mid-tones of a photo. It allows more precise control of a portion
of the brightness range than the levels tool but can be
harder to use. I prefer sticking with Levels. The curve can be shaped in any way, and the slope
of the curve will define the relation between input and output pixel
or brightness. This is a powerful tool for precise adjustments of
contrast in specific areas of a photo.
- Image size controls the number of pixels (picture
in the size of the image. Resolution can be confusing because
can have two very different results depending on the output device. In
a printed image, the resolution may control how sharp the picture
by putting more information in a given area of the image. On a computer
screen with a fixed display resolution, an increase in image size / resolution
cannot change the way the screen works; it will only make the image
using more screen area to display the additional information. Thus
is related to scaling or the size of the final image as related to the
size of the original. Doubling the resolution will make the final
image twice as wide and twice as tall, but the image file will be four
times as large (w/o compression).
- Automatic adjustments such as Photoshop's Auto Smart Fix can sometimes yield good results. But if you are unhappy with any adjustment, you can always undoo the change and try again.
Once an image is scanned and prepared, it must be saved as a
Files can be in GIF, JPG, PNG, or PICT format (among
Which to use?
- GIF - 256 colors, good compression, good for straight lines,
- JPG - millions of colors, excellent compression, compression is
but lossy (more compression = loss of image quality), good for photos
lots of colors, smooth color transitions.
- PNG - can be thought of as a compromise between GIF and JPG. It
for the WWW, but is not yet in very common use.
- PSD (PICT) - Photoshop default. No loss of quality on multiple saves. Best for a working copy that may need to be saved and reopened repeatedly. But the file size is very large and this will not work in a web page without conversion to GIF, JPG, or PNG. .
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