Welcome to a New Quarter

• Class Rules and Responsibilities• What will be learning? 106-Static and Dynamic Visualization 105-Synthesize Data for SciVis• Video-Real Life applications• 6.01: Recognize Digital Image Format• Finish Project

Digital Image Formats:An Explanation

V106.01E.Q: How are different digital image

formats used to demonstrate visualization processes?

File Formats• Every time you create a document or a graphic on

a computer, the item is saved with a particular file format. – Example: Yourname.doc has a .doc file format,

which identifies it a MS word file.• Just like different software programs are designed

to perform particular functions, different file formats are good at performing different tasks.

Native file formats• When you save a file using a particular program, that

program assigns its own individual format that is known as a native file format. Examples:

3Ds Max = .3dsPhotoshop = .psdMS Excel = .xlsCorel Draw = .cdr

• The native file format has advantages when you are working with the assigning program. For example, layers are retained when you save a Photoshop image with its native .psd file, but the layers are not available if you save the image what some other formats.

• Some companies design all of their products to work together, but you can have problems when you attempt to go from one company's product to another company's product.

Native file formats

Non-native file formats• The type of files that a

program will “open” or “save as” (other than its native format) vary with the individual program that you are using. Examples include bmp, jpeg, and txt files.

• Some software application programs will import (open) a wide range of other file formats, some will not.

File Compression• Compressed files are files that have been altered to produce a

smaller file size ( uses less memory). • Algorithms are programs that are written into software for file

compression.• There are two types of file compression, lossy and lossless.

Lossy Compression• Lossy compression results in a loss of data, and in turn, a loss of

image quality. A picture saved with lossy compression may not look as good as the original image.

• Lossy compression removes bits of color information in order to reduce file size.

• Once compressed, the image is permanently altered.

• Each compression change reduces image quality

Lossless Compression• Lossless compression reduces

the size of the image but results in an image that looks exactly the same as the original.

• LZW (Abraham Lempel, Jacob Ziv, and Terry Welch) is a popular lossless compression algorithm.

An Explanation of Digital Formats

Lossy vs. lossless compression

• Lossy compression loses some part of the file.

• Lossless compression does not lose any part of the compressed file.– LZW is an example of a

lossless compression algorithm.

Lossy compression will be missing part of the file to save space.

Image File Formats

TIFF (Tagged Image File Format)– TIFF is the best format for files that must go

cross-platform such as from a Windows system to a Macintosh computer.

– TIFF image are widely used and accepted within professional printing operations since it is of high quality.

– A TIFF Image can be a raster or a bitmapped image.

– TIFF images can be compressed using the lossless LZW compression system.

MAC

PC

An Explanation of Digital Formats

The file types - TIFF

• TIFF can be lossless or lossy. • The details of the image storage algorithm are included as

part of the file. • TIFF is used almost exclusively as a lossless image storage

format that uses no compression at all. • Most graphics programs that use TIFF do not use compression • File sizes are quite big.

– (Sometimes LZW is used, but it is not universally supported.)

Image File FormatsJPEG (Joint Photographic Experts Group)

– JPEG is actually a compression algorithm for static images, not a file format.

– JPEG’s are popular for photographs, artistic, and other complex images because they permit you to have 24 bit (16.7 million) color.

– The JPEG compression algorithm produces lossy compression. The algorithm exploits limitations of the human eye such as our inability to perceive small color details or details of light and dark.

Image File FormatsJPEG cont’d

– Most programs that create JPEG compression allow you to vary how much compression occurs so that you can trade off file size for image quality. The more compression that you use, the smaller the file size, but the greater the loss in image quality.

– A loss of quality might be acceptable for images that are used for images that are going to be printed.

– JPEG’s distort and blur color graphics.

An Explanation of Digital Formats

The file types - JEPG

• JEPG is optimized for photographs and similar continuous tone images that contain many, many colors.

• It can achieve astounding compression ratios even while maintaining very high image quality.

• The degree of compression of a JPG is adjustable.

Image File FormatsGIF (Graphical Interchange

Format)– GIF's are compressed graphic

images that are platform independent for use in any computer.

– It is a lossless format that uses LZW compression. It compresses at a ratio between 3:1 and 5:1.

– A GIF will support a maximum of 256 (8-bit) colors and is better suited for less complex images such as cartoons, simple clips art, or text.

– GIF images support transparency.

with

With out

Image File FormatsGIF cont’d

– Because CompuServe created GIF for use on the web, most have a resolution of 72 ppi, which does not make them very good for professional printing.

– GIF’s can be animated. The animation involves having additional image frames overlaying the main frame in a timed sequence.

– GIF compression is very good for use on images that contain lots of solid color.

An Explanation of Digital Formats

The file types - GIF

• GIF creates a table of up to 256 colors from a pool of 16 million.

• If the image has fewer than 256 colors, GIF can render the image exactly.

• GIF is "lossless" only for images with 256 colors or less. For a rich, true color image, GIF may "lose" 99.998% of the colors.

Image File Formats

BMP (bitmap)– BMP files are used for bitmap

images within the windows operating systems.

– Most often used for certain screen backgrounds for Windows operating system.

– Can be compressed and other controls applied, but it is seldom used by third party software.

An Explanation of Digital Formats

The file types - BMP

• BMP is an uncompressed proprietary format invented by Microsoft.

• There is really no reason to ever use this format.

Image File Formats

AVI (Audio Visual Interleaved)– AVI’s are sound and motion

picture files that were developed by Microsoft for storing audio and video data.

– AVI is a popular and widely distributed format because is can be displayed using the Windows Media Player that comes with Microsoft operating system

An Explanation of Digital Formats

The file types - PNG

• PNG is a lossless storage format. • It looks for patterns in the image that it can

use to compress file size. • The compression is exactly reversible, so the

image is recovered exactly.

An Explanation of Digital Formats

The file types - PSD

• PSD is a proprietary format used by Photoshop. • This is the preferred working format to edit images in the

software• This package uses layers to build complex images, and layer

information may be lost in the nonproprietary formats such as TIFF and JPG.

• However, it is best to save the product as a TIFF or JPG, so it can be viewed in the future when software changes.

An Explanation of Digital Formats

An explanation

• Why so many file formats?• How are they used?• One reason is compression,

lossy or lossless.• Another reason is the

number of colors to be used.

An Explanation of Digital Formats

Number of colors• Images have differing numbers of

color within them.• Black and white images take up the

least amount of space with 1 bit of information.

• Current video cards are able to display 24 bits of color per pixel.

• This makes it possible for 16 million colors to be displayed (224 colors).

• This requires a significant amount of disk space.

An Explanation of Digital Formats

When should you choose each?

• TIFF – This is usually the best quality output from a digital camera.

• JPG – This is the format of choice for nearly all photographs on the web.

• GIF - For images with fewer than 256 colors and large areas of uniform color like cartoons.– Do NOT use GIF for photographic images

• PNG - For images with large areas of exactly uniform color, but more than 256 colors – Also, for display of photographs exactly without loss of quality on the

web.

An Explanation of Digital Formats

The file types - Summary

• TIFF files are generally large.• PNG compression can be reversed if needed.• GIF results in lose of color information.• JEPG are the best in terms of compressed files.• BMP should be rarely, if ever used.• PSD is exclusive to Photoshop.

An Explanation of Digital Formats

File size comparisons• TIFF (901 kb)

http://www.wfu.edu/~matthews/misc/graphics/formats/uncompr.tif

• JPG (301 kb) http://www.wfu.edu/~matthews/misc/graphics/formats/HiQ.jpg

• PNG (741 kb) http://www.wfu.edu/~matthews/misc/graphics/formats/png.png

• GIF (131 kb) http://www.wfu.edu/~matthews/misc/graphics/formats/optmedcut.gif

An Explanation of Digital Formats

Reference

• Matthews, R. (2007). Digital image file types. Retrieved June 21, 2007 from http://www.wfu.edu/~matthews/misc/graphics/formats/formats.html.

An Explanation of Digital Formats

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