Scanning
- 1-bit
- Another term for a line-art scan file or scanner setting.
Refers to the number of bits (1) in the data. With one bit a pixel
will either be black or white.
- 12-bits per color
- A feature found in some desktop scanners. This feature allows
the capture of much greater shadow detail (when compared with
8-bits) and allows the scanner to create a more satisfactory scan
from an original that may be low in contrast.
- 24-bit Scanner
- A 24-bit scanner can capture 8-bits of data in each of the
red, green and blue colors.
- 36-bit Scanner
- A 36-bit scanner can capture 12-bits of data in each of the
red, green and blue colors. The data will be analyzed and dropped
to 24-bits of data but through this process, image quality is
enhanced.
- 8-bit
- Another term for a Greyscale scan file or scanner setting.
Refers to the number of bits (8) in the data. With 8-bits per
pixel the image will have 256 shades of grey. This is a sufficient
number of grey values to create a quality black and white
photographic reproduction.
- Bitmapped Image
- A bitmapped image is a computer file representing a line-art
image that was scanned with a scanner. Refers to the pattern (map)
of bits that are either black or white.
- Black Point Adjustment
- An adjustment made that will determine the amount of shadow
detail in an image. It is considered proper to set the black point
so that the darkest part of an image will only just have zero
detail.
- Brightness Adjustment
- An adjustment on a scanner that allows the user to compensate
for a light or dark original.
- CCD
- Stands for Charge Coupled Device. Essentially a light
sensitive computer chip, a CCD is the optical element in a CCD
scanner that converts light to voltages. The more light a CCD
receives, the higher voltage it creates. These voltages are
converted by the scanner into the images we see.
- Color Correction Adjustment
- The act of correcting for and eliminating an unwanted color
cast. Part of the scanner set-up, a preview image is measured on
the computer display and adjusted so that the color measures in
the desired way. After this adjustment is made, the actual scan is
performed using these color correction settings.
- Color Space
- A color space is a particular language used to describe color.
Examples of color spaces are: RGB, CMYK, HSB, CIE LAB.
- Contrast
- The range between lights and darks in an image. Proper
contrast is important so that an image appears realistic.
- Contrast Adjustment
- That act of adjusting contrast for proper visual results.
- Curve
- As in tone curve, or color correction curve. Beginning as a
45° angle line running up to the right, this line is adjusted
into a curve shape by the user to effect color or tone correction.
The lower left end of the curve typically represents the dark
portions of a picture and an upward bend will typically lighten
the shadows. Similar capabilities exist by working with the middle
or highlight parts of the curve. In this way it is possible to
alter only certain tone ranges of an image without making
un-wanted changes in other parts of the image.
- DPI
- An improper expression of the resolution of a scanned image.
The expression pixels per inch (PPI) is the correct indication of
scanned image resolution. DPI (standing for dots per inch) is used
in expressing the resolution of a laser printer or other output
device.
- Drum Scanner
- A type of scanner on which original artwork is attached to the
outside of a spinning glass drum. The image is scanned by photo
multiplier tubes (PMTs) and is captured to a disk file. This type
of scanner gives the best quality result.
- Dynamic Range
- An expression of the density difference between highlights and
shadows. As a measurement of scanner quality, dynamic range is one
of the primary differences between low and high quality scanners.
A desktop scanner with a small dynamic range will yield scanned
images that lack detail in shadow areas.
- Flatbed Scanner
- A type of scanner with a light sensing CCD element on a moving
carriage mounted under a sheet of glass. Artwork is placed face
down on this glass and covered with a hinged cover. A flatbed
scanner has much in common with the top portion of an office
copier.
- FPO Scan
- A low-resolution photographic scan (usually 72 PPI) used for
composition purposes only. After laser hardcopy is produced, the
FPO image is replaced with a different (high-resolution) scanned
image.
- Gradation Adjustment
- An adjustment leading up to performing a scan where the user
makes adjustment to the brightness and color balance of the image.
After performing a preview scan, the user will adjust the tone
correction curves of their scanner to achieve natural color.
- Grayscale Image
- A term for a black & white photographic scan file. Refers
to the range of 256 grey tones that make up the image.
- Grey Balance Adjustment
- A color correction adjustment to insure that grey elements
within a scanned image appear as a neutral grey. It is generally
considered proper technique to adjust the image so that neutral
grey elements appear neutral gray. If this is done, it will
usually be true that other elements within the image will also
have true color reproduction.
- High-resolution Image
- A term used to describe an image with enough detail (achieved
through having plenty of pixels per inch) for quality reproduction
and use in final film. How high the resolution should be depends
on the image type: Line-art should have resolution of 600 PPI or
above and photographs should have resolution twice the anticipated
halftone screen frequency.
- Interpolation
- A function found on low cost scanners where optical resolution
(expressed as PPI) is enhanced through software enhancement. In
this way, a 300 PPI scanner can create 600 PPI files.
Interpolation does not give as good a result as a scanner with
higher optical resolution. (The software won't be able to enhance
detail the scanner doesn't see in the first place.)
- Low-resolution Image
- A low-resolution photographic scan (usually 72 PPI) used for
composition purposes only. After laser hardcopy is produced, the
low-resolution image is replaced with a different
(high-resolution) scanned image.
- OPI
- Open Prepress Interface. A term relating to the use of special
low-resolution versions of high-resolution images. This process
offers faster page layout. These low resolution images are
automatically exchanged for the high-resolution version when the
layout is output.
- PhotoCD
- A technology from Kodak that allows photographic images to be
stored on a CD-ROM disc. These PhotoCD images can be displayed on
a television set or can be used in a desktop page layout and
separated to film. A complex technology, the achievable quality
depends on a talented computer operator with knowledge of color
prepress techniques. That in hand, PhotoCD can achieve above
average quality color separations for a low unit cost.
- Pixel
- The smallest building block within a scanned line-art or
photographic image. A pixel is the small square picture element
that is filled with a color, or black or white. Pixels come in
various sizes and their size is expressed in terms of resolution.
Resolution is measured in pixels per inch (PPI.)
- PMT
- Photo Multiplier Tube. A light sensing element used in high
quality drum scanners. It is said that scanners using PMT
technology create the highest quality scans.
- PPI
- Pixels Per Inch. An expression of resolution of a scanned
image.
- Resolution of a Scanner
- Expressed as PPI (pixels per inch.) The resolution of a
scanner limits the enlargement capabilities of the device. Optical
resolution is the resolution of the device and interpolated
resolution is resolution enhanced by software and is the res.
frequently touted in scanner advertisements. Interpolated
resolution does not always yield significant detail enhancement.
- Shadow Detail
- A term that refers to the amount of detail contained in the
dark parts of an image. It is desirable to maintain shadow detail
but there is a risk of decreasing overall contrast if one lightens
the shadow too much in an attempt to expose detail. If an image is
scanned without shadow detail, it will be impossible to regain
detail in an image editing program.
- Sharpness
- An attribute of a scanned image and also an attribute of a
good quality scanner. It is considered desirable for an image to
have good sharpness.
- Tone Curve
- A term for an adjustment available on certain scanners.
Beginning as a 45° angle line running up to the right, this
line is adjusted into a curve shape by the user to effect color or
tone correction. The lower left end of the curve typically
represents the dark portions of a picture and an upward bend will
typically lighten the shadows. Similar capabilities exist by
working with the middle or highlight parts of the curve. In this
way it is possible to alter only certain tone ranges of an image
without making un-wanted changes in other parts of the image.
- Unsharp Masking
- An important function that allows the user to add apparent
clarity via electronic means. Unsharp masking is considered the
most sophisticated sharpening method because it sharpens without
the undesirable graininess that appears with other sharpening
methods.
- White Point Adjustment
- An adjustment made that will determine the amount of highlight
detail in an image. It is considered proper to set the white point
so that the lightest part of an image will only just have zero
detail.