This is the first article in our blog about images. That’s why we decided to talk talk a little about the image types. If you are an experienced user you may know all those, but if you are a novice in computers, you may noticed that you can find several image formats out there. The most common are JPEG (JPG), GIF, BMP, PNG, TIFF, WMF, PCS, ICO and many, many others. Those listed previosly are the most used ones.

Let’s take each one and talk about the most used image files formats a little bit.

- JPEG (Joint Photographic Experts Group)

Format name: JPEG (Joint Photographic Experts Group)
Extension: jpg, jpeg, jfif,jfl
Type: bitmapped
Compression algorithm: JPEG (lossy)
Color depth: 24 bits
Platforms: all
Jpeg (or Jpg) format was first created to transfer graphic data and images via digital telecommunication networking and was generally used to keep and transfer full color photo realistic images. Before Jpeg, there were very few image formats, which supported 24 bit halftone images. TIFF and BMP formats allowed holding 24 bit data, but those weren’t able to perform a  data compression without loss, which contained thousand and thousand  colors from the real world, on the high quality level.

Jpg format can compresses images though with some quality loss. Compression algorithm is that data are deleted for de-allocation (this means it allows to raise the degree of the compression). Pixel data are hold as pixel block in a certain color with intensity information save.

Pictures and multi-color images, transferred in this JPEG format, are ideal for internet use. Jpeg format is primarily used to have graphic images with a large number of colors.

Compressed data capacity in JPEG image files depends on image contents. Compression degree may come up to 25:1 , and this without visible loss in quality.

Jpeg supports “Progressive Jpeg standard”, which is very similar to interlaced in Gif format. In this way, Jpeg Progressive format images are loaded by parts, which are displayed, as they are loaded. Such Progressive format is very useful for large files. But this is a pretty new starndard, and  some programs may not support it.

- GIF (Graphics Interchange Format)

Format name: GIF (Graphics Interchange Format)
Extension: gif
Type: bitmapped
Compression algorithm: LZW (lossless)
Color depth: up to 8 bits
Platforms: all
Versions: gif87 and gif89
Released in: 1987

Gif picture file format is used to hold and transfer images in index color mode (maximum 256). GIF image format also supports a LZW compression algorithm (a single file may contain a set of images) and also interlaced image load.

The GIF format was updated in 1989, and named gif89. It supports an additional channel to perform a transparency effect and to keep a set of images in a single file .

In these days, GIF format is one of the most popular and used graphic files formats. Though it not suited to keep a photo-realistic images, beacause this kind of format cannot contain more than 256 colors.

Gif format, unlike Jpeg format, use a loss-less compression algorithm. That means that while compression/decompression bits are not deleted. Gif uses a patent compression /decompression algorithm, which is called LZW (Lempel Zev Welch).

- Bitmap (Microsoft Windows Bitmap)

Format name: Bitmap (Microsoft Windows Bitmap)
Extension: bmp, dib, rle
Type: bitmapped
Compression algorithm: RLE (lossless), without compression
Color depth: up to 32 bits
Platforms: Windows, OS/2

Bitmap is a Windows raster format, which is used practically for all possible raster data storage.
All BMP versions were designed for computers with Intel processors. The current format version is device independable (that means that Bitmap determines the pixel’s color without reference to display device) and makes possible to record images of a different quality level (to the point of 32 bits).

The main advantage of the BMP file format is its usability and wide software support.

- PNG (Portable Network Graphic)

Format name: PNG (Portable Network Graphic)
Extension: png
Type: bitmapped
Compression algorithm: Deflate (lossless)
Color depth: up to 48 bits
Platforms: all

Png file format is a a new progressive format originally designed to replace old dated Gif. PNG format has got a set of new features that GIF image format don’t have.

Png also performs a loss-less compression with the help of Deflate algorithm and supports interlaced mode. The format handles 256 transparency levels which means that images might be partially transparent. They won’t lose its quality while compressing and decompressing. The fact that the PNG supports color depth up to 48 bits and performs a loss-less compression, makes possible to hold photo-realistic images.

Png format is used specially for networking and internet use.

TIFF (Tagged Image File Format)

Format name: TIFF (Tagged Image File Format)
Extension: tif
Type: bitmapped
Compression algorithm: CCITT-RLE, CCITT-FAX3, CCITT-FAX4, LZW, OJPEG, JPEG, CCITT-RLEW, Packbits, Deflate
Color depth: up to 48 bits
Platforms: all
Released in: 1986

This image format was released in 1986 and was generally used to keep scanned black and white images.

Released in 1987, Tiff 4.0 got prevalence for it supported incompact color RGB images. In 1988 was released Tiff 5.0 format, which made possible to hold palette color images and support LZW compression algorithm. Released in 1992, Tiff 6.0, supported CMYK and YcbCr color images and Jpeg compression algorithm.

Finally, the current Tiff (Tiff 6.0) is a rich and flexible file format, supported by many software out there. The format is capable to record halftone images with different pixel intensity. So, TIFF format is considered to be a perfect format for graphic data storage and processing.

- PCX (PC Paintbrush File format)

Format name: PCX (PC Paintbrush File format)
Programmer: Zsoft
Extension: pcx
Type: bitmapped
Compression algorithm: RLE, without compression
Color depth: 1, 4, 8, 24 bits
Platforms: all

PCX format is one of the most usable graphic formats. Originally it was designed by Zsoft for MS-DOS Paintbrush. That is why, it is also known as PC Paintbrush format. Zsoft entered into a treaty with Microsoft. The latter was entitled to use PCX format with other products, including Microsoft Paintbrush for Windows (Microsoft Paintbrush program is delivered with each copy of MS Windows).

Originally the format was used to hold graphics and images, which contained not more than 16 colors. This limitation was conditioned by IBM EGA display construction (Enhanced Graphics). When IBM started to release VGA adapter (Virtual Graphics Array), PCX format was revised to hold graphics and images, which contained up to 256 colors.

The last PCX versions make possible to hold 24 bits color displays. Unfortunately, its compression algorithm is not effective enough to hold images with large pixel intensity.

Graphics data are encoded with the help of RLE algorithm. Using RLE, it is difficult to foresee the end, for compressing factor is highly depended on image data and on the number of colors, used in the concrete. Generally, image data, which contain not more than 16 colors, decrease by 40-70% as compared with the original file size. While 64 or 256 color images, which were scanned or videoed, decrease only by 10-30%. Sometimes you can increase PCX file size via using compression algorithm for complex images.