| Q.
|
Resolution |
| A.
|
The
number of pixels displayed per unit of printed length
to represent a bitmap image. Usually, resolution
is measured as dots per inch (dpi) or pixels per
inch (ppi). |
|
|
| Q. |
Pixels |
| A. |
The
smallest element that can be displayed on a screen
or printer, in other words it's the smallest picture
element unit in an image. |
|
|
| Q. |
DPI |
| A. |
An
acronym for dots per inch, a measurement of resolution.
Higher the DPI higher is the scanned image resolution.
|
|
|
| Q. |
LPI (Lines Per Inch) |
| A. |
A
term used in printing as a measurement of the frequency
of lines on a screen (usually ranging from 55-200).
LPI refers to the frequency of the horizontal and
vertical lines. |
|
|
| Q. |
PPI
(Pixels Per Inch) |
|
A.
|
A
measurement of the amount of scanned information.
The finer the optics of the scanner the higher the
scan resolution. PPI is equivalent to DPI. |
|
|
| Q.
|
Preview |
| A. |
An
operation that gets a rough image of a document
for setting parameters and image analysis. |
|
|
| Q. |
Image Type |
| A. |
According
to the contents of your documents, the image can
basically be divided into three types. |
| |
1 |
Line
Art
The Line Art image type is used for documents containing
lines, text and detailed drawings. If OCR (Optical
Character Recognition) software is used for document
management, the Line Art image type should be selected
and the resolution be at 300 dpi or higher. When
the original is a negative film, this type is unavailable.
|
| |
2 |
Grayscale
A grayscale image is composed of pixels with 8 bits
(256-shades) and contains only white, black and
intermediate shades of gray. |
| |
3 |
Color Image
The Color Image type is used for images with continuous
tones and with lots of gray shades or colors. Color
photos contain more information than any other type
of images, but they also occupy much more disk space
and system memory. |
|
|
| Q. |
Bit
depth |
| A |
Also
known as pixel depth, it defines the number of bits
used to represent each pixel in an image. It also
determines how many colors every pixel in a bitmap
can have. In other words, the depth of information
recorded during the scanning process is limited
by the chosen bit depth. |
|
|
| Q. |
Optical
Resolution |
| A |
This refers to the number readings taken from an
original image within a given distance, as opposed
to the subsequent increase in resolution (but not
detail) created by software interpolation. |
|
|
| Q. |
Maximum
Resolution (Interpolated Resolution) |
| A. |
The process of increasing the resolution of an image,
with the help of a software, by the addition of
new pixels throughout the image, the colors of which
are based on neighbouring pixels. For example, to
create another dot between adjacent dots of Red
values 100 and 108, the new dot can be assumed to
have red value 104, so the transmission is 100,
104, 108. The same is done for Blue and Green, and
the image will look smooth and larger. |
|
|
| Q. |
Interface |
| A. |
Interface is the type of connection used. The four
most common types are…
- Parallel (uses 25pin connector, same port
that a printer would use)
- USB (short for Universal Serial Bus, common
on newer computer systems)
- SCSI (Small Computer System Interface,
requires SCSI controller, very fast)
- Firewire (Extremely fast IEEE 1394 connection,
requires firewire card) |
|
|
| Q. |
Image
Size |
| A. |
A
large image size will lower the system performance
of your computer dramatically. The file size is
affected by the selected area, file format, scaling
ratio, resolution and the image type. The following
table presents the detailed information (file compression
is excluded): |
| Image
Type |
Description |
|
1-bit images |
Black
and White Line Art |
| 8-bit
images |
Black
and White or Color Image, 256 gray levels
or 256 colors |
|
24-bit images |
Color
Image, Millions of Colors |
|
32-bit images |
Color
Image, Billions of Colors |
|
|
|
| Q. |
File
Formats |
| A. |
File
format determines the structure of information to
be saved in a file. Refer to the following table
to obtain better performance. |
| File
Format |
File
Extension |
Advantages |
|
TIFF |
.tif |
•
Efficient file size
• Can save color separations |
|
EPS |
.eps,
.epsf |
•
Can save duotone information
• Can save clipping path
• Can save color separations |
|
PCX |
.pcx |
•
Used by most software applications |
|
PICT |
.pict,
.pct |
•
Has Compact file size |
|
BMP |
.bmp |
•
Used by most software |
|
Targa |
.tga |
•
Can save alpha channel |
|
JPEG |
.jpg,
.jpeg |
•
Has the best compression ratio |
|
|
|
| Q. |
Compression |
| A. |
Encoding
the bits of information in an image file so that
it takes up less space when stored. Compression
results in little or no distortion. File compression
falls into two general categories: |
•
Lossy compression and
• Lossless compression |
|
|
| Q. |
Lossy
compression |
| A. |
Lossy
compression assumes that some of the data
in the image file is unnecessary and can
be eliminated without affecting the quality
of the image scanned. Typically this type
of compression has ratios between 10:1 and
100:1.
|
| The
most popular lossy compression option is JPEG. JPEG
stands for the Joint Photographic Experts Group,
which developed the compression standard. JPEG compression
ratio is selectable in the host software and ranges
from 2:1 up to 40:1. |
|
|
| Q. |
Lossless
compression |
| A. |
Lossless
compression stores image data in a file without
deleting information, that is, no loss of image
details, color or output quality.
If the 2:1 compression ratio is enough, lossless
compression can to be considered.
|
