Image
processing is a broad area. Image is nothing but a combination of pixels. It has
various file formats.
1) BMP (Bitmap
file format)
2) JPG (Joint
Photographic Expert Group)
3) TIF (Tagged
Image file format)
4) PNG (Portable
Network Graphics)
5) PPM, PGM,
PBM, PNM and PFM
6) RAW (Raw Image format)
BMP:
The BMP file
format (Windows bitmap) handles graphics files within the
Microsoft Windows OS. Typically, BMP files are uncompressed, hence they are
large; the advantage is their simplicity and wide acceptance in Windows
programs.
JPG:
JPEG (Joint Photographic
Experts Group) is a compression method; JPEG-compressed images are usually
stored in the JFIF (JPEG File
Interchange Format) file format. JPEG compression is (in most cases) lossy
compression. The JPEG/JFIF filename extension is JPG or JPEG. Nearly
every digital camera can save images in the JPEG/JFIF format, which supports
8-bit grayscale images and 24-bit color images (8 bits each for red, green, and
blue). JPEG applies lossy compression to images, which can result in a
significant reduction of the file size. The amount of compression can be
specified, and the amount of compression affects the visual quality of the
result. When not too great, the compression does not noticeably detract from
the image's quality, but JPEG files suffer generational
degradation when repeatedly edited and saved. (JPEG also provides
lossless image storage, but the lossless version is not widely supported.)
TIF:
TIF is
lossless (including LZW compression option), which is considered the highest
quality format for commercial work. The TIF format is not necessarily any
"higher quality" per se (the image pixels are what they are), and
most formats other than JPG are lossless too. This simply means there are no
additional losses or JPG artifacts to degrade and detract from the original.
And TIF is the most versatile, except that web pages don't show TIF files. For
other purposes however, TIF does most of anything you might want, from 1-bit to
48-bit color, RGB, CMYK, LAB, or Indexed color. Most any of the
"special" file types (for example, camera RAW files, fax files, or
multipage documents) are based on TIF format, but with unique proprietary data
tags - making these incompatible unless expected by their special software.
PNG:
PNG
can replace GIF today (web browsers show both), and PNG also offers many
options of TIF too (indexed or RGB, 1 to 48-bits, etc). PNG was invented more
recently than the others, designed to bypass possible LZW compression patent
issues with GIF, and since it was more modern, it offers other options too (RGB
color modes, 16 bits, etc). One additional feature of PNG is transparency for
24 bit RGB images. Normally PNG files are a little smaller than LZW compression
in TIF or GIF (all of these use lossless compression, of different types), but
PNG is perhaps slightly slower to read or write. That patent situation has gone
away now, but PNG remains excellent. Less used than TIF or JPG, but PNG is
another good choice for lossless quality work.
PPM, PGM, PBM, PNM and PFM:
Netpbm format
is a family including the portable
pixmap file format (PPM), the portable
graymap file format (PGM) and the portable bitmap file format (PBM). These are either pure ASCII files or raw binary
files with an ASCII header that provide very basic functionality and serve as a
lowest common denominator for converting pixmap, graymap, or bitmap files
between different platforms. Several applications refer to them collectively as
PNM or PAM format (Portable Any Map). PFM was invented later in order to carry
floating-point-based pixel information (as used in HDR).
RAW:
RAW
refers to raw image formats that are available on some
digital cameras, rather than to a specific format. These formats usually use a
lossless or nearly lossless compression, and produce file sizes smaller than
the TIFF formats.
GIF
(Graphics Interchange Format) is limited to
an 8-bit palette, or 256 colors. This makes the GIF format suitable for storing
graphics with relatively few colors such as simple diagrams, shapes, logos and
cartoon style images. The GIF format supports animation and is still widely
used to provide image animation effects. It also uses a lossless compression
that is more effective when large areas have a single color, and ineffective
for detailed images.
Best Image file Types:
Photographic
Images
|
Graphics,
including
Logos or Line art |
|
Properties
|
Photos are
continuous tones, 24-bit color or 8-bit Gray, no text, few lines and edges
|
Graphics
are often solid colors, with few colors, up to 256 colors, with text or lines
and sharp edges
|
For Unquestionable Best Quality
|
TIF or PNG
(lossless compression
and no JPG artifacts) |
PNG or TIF
(lossless compression,
and no JPG artifacts) |
Smallest File Size
|
JPG with a
higher Quality factor can be decent.
|
TIF LZW or
GIF or PNG (graphics/logos without gradients normally permit indexed
color of 2 to 16 colors for smallest file size)
|
Maximum Compatibility
(PC, Mac, Unix) |
TIF or JPG
|
TIF or GIF
|
Worst Choice
|
256 color
GIF is very limited color, and is a larger file than 24 -bit JPG
|
JPG
compression adds artifacts, smears text and lines and edges
|
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