Image conversion in computers
JPEG, GIFF/JIFF, BMP, and TIFF are the most commonly used formats for storing still image files such as photographs, graphics, and drawings. JPEG stands for Joint Photographic Experts Group and is a standard for image compression.
However, some amount of data/detail is lost in the process. JPEG therefore is characterized by a glossy compression technique for still color images, just as MPEG is used for compressing motion picture files.
GIFF/JIFF stands for Graphics Interchange format, which is a bit-mapped graphics file format.
Its storage is limited to about 256 colors as against 16 million colors in JPEG. GIFF therefore is more suitable to store illustrations rather than color photos.
Other popular formats for storing bit-mapped images are TIFF (Tagged image file format), BMP,and PCX. You'll also see GIF and JPG. You may be wondering what a bit-map is? A bit-map graphic is composed of a pattern of dots (each dot containing bits of data). Vector graphics, on the other hand, use geometrical formulas to represent images. The latter can be scaled i.e. the object size can be changed while maintaining its shape. Vector images are thus more flexible than bit-maps. Also vector imageslook better on higher resolution and require less memory. This brings us to the difference between Paint programs and Draw programs. In Paint program the drawings are represented as bit-maps. Draw programs, on the other hand, represent images as vector graphics.
Why we need to convert images from one format to another?
? Converting GIFF files to JPEG can compress the files to a considerable extent. The uncompressed data is normally 24 bits/pixel for full-color images. JPEG can achieve 10:1 to 20:1 compression without apparent loss, 30:1 to 50:1 compression with small to moderate defects, and 100:1 for very low quality purposes like archiving. These smaller size files increase storage capacity and take lesser transmission time across networks.
? JPEG files are extremely useful for image archiving purposes. JPEG files store a full color range (24 bits/pixel as against 8 bits/pixels in GIFF).The display of images is particularly good on full-color hardware that is becoming common now.
Conversion rules:
? Large, high-quality, real-world scanned photos are the best material for conversion to JPEG format.
? Do not convert black and white images to JPEG that works best with smooth and subtle color palette. B&W images are best on GIF.
? Even on colored images make sure to smoothen out the sharp edges before carrying out the conversion. A gray-scale image is much easier for a JPEG format.
? Avoid converting images that have already been converted before. Re-conversion spoils the quality of images. It's best to work with original scanned images here.
To explain how format conversion is carried out here's an example:
1. In a Windows operating system go to Start menu ? Accessories ? Paint
2. Create an image with the program and save it in BMP format. Now Close the file
3. To convert it into say JPEG, re-open the file
4. Go to File menu and click Save As
5. Rename the file in File name box and in Save as Type drop down box click on the format you want it to be converted to. In this case "JPEG File Interchange Format (*.jpg, *. jpeg,)"
6. Click on the Save button. Your file is now converted from BMP to JPEG.
If you want to change BMP to GIF, follow the same procedure except that in Save as Type box click on "Graphics Interchange Format (.gif)"
Once an image has been converted from one format to another, say GIF to JPEG, some of the information is lost. You can't go back to the original file. Therefore it is always advisable that you make a copy of the original file before converting it.
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