 |
|
|
|
|
 |
|
Home  JPEG |
Newest Photos Most Popular Photos |
|
|
JPEG Quality Levels
If you save images in JPEG format some original image information will be lost, due to how JPEG compresses images. Considering that our eyes perceive small color changes less accurately than small changes in brightness, JPEG averages the color data in blocks of 8 by 8 pixels. An advantage of using JPEG is that file sizes will be considerably smaller than with lossless compression methods such as TIFF.
Although digital images can be compressed at up to 100 JPEG quality levels most digital cameras that use JPEG let you save the images at three settings, usually marked Fine, Normal or Low, though the exact terms used may vary from one manufacturer to the other.
This means that you have a choice as to how much information will be lost during compression and consequently what the final quality of your image will be.
As it is not always possible to determine beforehand what an image will be used for, we would advise you to always use the highest quality setting, since information lost can never be retrieved. Also, with more image information available, correcting or sharpening an image without perceivable quality loss will be much easier. Repeatedly opening and saving a JPEG image will lose a little more image quality each time, since an already compressed image will be compressed again, causing even more information to be lost.
JPEG GIF File Formats
The JPEG format (Joint Photographic
Experts Group) which supports 24-bit color, can be read by many applications because
it is a standardized image compression mechanism. Created especially for the transmission
and storage of photographic images, it offers a significant reduction in
file size.
It uses a lossy compression scheme by averaging the data in blocks of
8 x 8 pixels. Color variations that existed in the original image are lessened.
JPEG can achieve very high compression factors, the amount of which can be varied.
But beware, since every time you open and save a JPEG file the image is compressed again so
repeatedly saving the same image will seriously degrade it.
The GIF format (Graphic Interchange Format) which was developed by Compuserve in 1987,
can only show 256 colors but it can choose any of the 16 million colors in a 24-bit image.
These colors are stored in an index. It uses a lossless compression scheme.
An advantage over JPEG is that it handles images with a lot of contrast and fine
details better than JPEG. This is the reason it is mostly used for line art such as
cartoons, logos and text, and not so much for photographic images. JPEG and GIF are
the most widely used formats on the Web nowadays.
Photography-Camera News Index
|
|
|
|
WE ACCEPT  |
|
|
