Fatih Özlü

Image File Formats

Content Introduction to Image File Formats

Image File Types (Bitmap/Vector)

Key Terms for Images

Pixels

Pixel Depth

Compression Methods: Lossy-Lossless

Common Image File formats

JPEG

PNG

GIF

BMP

Conclusion

Why so many Image File Formats?

… - BMP – PBM – TGA – TIFF – GIF – JPEG –

PSD – DXF – CGM – PNG – SVG – RAW –

WPG – FITS –PCX– PCD – RAS – TGA – BPS –

EPS – PDF – PCT – WBM – FITS – XBM – VFF

– RIB – PCX – DMP – AVS – IMG – ICO – JFIF

– IFF –WMF - …

Image File Types Bitmap(Raster) images:

collection of dots

each pixel can hold 1,8,24,… bit of color information

fixed resolution

best for photographic quality images, for printing, scanners, digital cameras

examples: bmp, gif, png, jpeg, tiff, …

Vector graphics:

based on mathematical instructions

basically defined by shapes and lines

not resolution dependent: infinitely scalable

examples: svg, ai, wmf, …

Metafile graphics:

combination of bitmap and vector

Pixels

image elements

smallest addressable part of the screen

stored as a binary code representing a color

between 1 and 32 bits of binary code

RGB (Red, Green Blue)

CMYK (Cyan, Magenta, Yellow, Black)

resolution

density of dots on image

measured in DPI (dots per Inch)

Pixel Depth

Images retrieved from http://en.wikipedia.org/

number of bits to store each pixel

greater depth, more colors

greater depth, bigger file size

monochrome : 1 bit(white and black)

grayscale, 16, 256 color

truecolor: 24 bit

1 bit 2 bit 4 bit 8 bit 24 bit

Compression

large amount of data

lossy/lossless

quality

Some algorithms

LZW(Lemple-Zif –Welch) Algorithm

RLE Algorithm

ZIP Compression

JPEG Compression -> lossy

Deflation – used in PNG, MNG, and TIFF

JPEG (Joint Photographic Experts

Group) most applications and browsers, digital cameras

good compression algorithm : reduce file size in a ratio between 10:1 and 20:1.

degree of compression is adjustable

lossy compression

not support transparent color

not interlaced:???

extensions: .jpeg, .jpe, .jpg, .jif, .jfif, .jfi

Higher quality (Q = 100) High quality (Q = 50) Medium quality (Q = 25) Low quality (Q = 10) Lowest quality (Q = 1)

83,261 bytes 15,138 bytes 9,553 bytes 4,787 bytes 1,523 bytes

the uncompressed 24-bit RGB bitmap image below 313 × 234 image (73,242 pixels) would require 219,726 bytes

GIF (Graphics Interchange Format)

most widely used

few colors: 8 bit or less

LZW lossless compression algorithm

less space, less loading time

interlaced and non-interlaced

supports animation: can contain

more than one image

LZW algorithm patent issue

resulted PNG.

PNG (Portable Network Graphics)

developed due to legal problems with compression algorithm

PNG's Not GIF

new format targeted for Internet use, becoming common

lossless compression (more than GIF, less than JPEG)

24-bit RGB, 32-bit RGBA or up to 48 bit color

transparency (A:Alpha channel)

no animation support

better interlacing: Adam7 algorithm

Illustration of the 7 passes of the Adam7 algorithm,

running over a 16×16 image

BMP (Bitmap Image File)

Microsoft native image format

Windows,OS/2, no MAC compatibility.

backgrounds, graphics, wallpaper

1(monochrome), 4, 8, 24-bit RGB

generally uncompressed, too large size

lossless RLE compression

Conclusion compression

larger file, larger storage and slower download

few color, smaller file, worse quality

There is really no reason to ever use this format BMP

GIF and JPG are the formats used for nearly all web images. PNG is supported by most of the latest generation browsers.

But Microsoft Internet Explorer does not support PNG transparency.

PNG does everything GIF does, and better, so expect to see PNG replace GIF in the future. PNG will not replace JPG, since JPG is capable of much greater compression of photographic images, even when set for quite minimal loss of quality

Thanks

Questions?