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Acquisition & Save

Images Format

Matrix Formats

A matrix format is characterized by recording data in table shape. The pixels are ordered with coordinates, an ordinate and an abscysse associated with a color value.

Bitmap (BMP)

The format is the easiest. The compression of this format is rarely used. Indeed, it is only available for 8 and 4-bit BMP. The algorithm used is the Run-length encoding (RLE).

We can see below 4 Bitmap images with from left to rigth 24bits, 8bits, 4 bits et 1 bit.
image bmp bitmap
Thoses images have a size of 256 by 256 pixels. The size of files are : 260Ko, 68ko, 36Ko et 12Ko.

Graphics Interchange Format (GIF)

For this format, up to 256 different colors can be chosen. In other words, a pixel is coded on one byte. This allows a very good compression without loss by the algorithm Lempel-Ziv-Welch (LZW). This format is very popular for icons and logos. In addition the GIF89a revision enables the creation of sequence succession of animated images.

Tagged Image File Format(TIFF)

The TIFF format can save large bitmaps of several GBs and without loss of quality. The colors can be coded from 1 to 64 bits for a wide range of color space: RGB, YCbCr, CMYK, CIE Lab. A wide choice of compression is also available: PackBits, LZW, CCITT, JPEG. Furthermore, additional information can be added as the contrast or brightness.

Portable Network Graphics (PNG)

Alternative format of the GIF format, it is free. No Royalties shall be paid by software publishers who using it. It allows you to store images to gray level upto 16 bits precision or 48 bits for color. The constitution of the file is made of chunks. All segments are made in the same way.

The chunks can be mixed but the header chunk IHDR must be put first and IEND end chunk at the end. There are many segments (the first 4 are required):


Joint Photographic Experts Group (JPEG)

This format is actually a standard decoding. The method of encoding is left free to industrialists and academics, the important is that the resulting file can be decoded by the JPEG standard. Two types of compression can be used for this format, lossy compression (irreversible) or we see a loss of information but in return the file. jpg is much smaller. The other type is a lossless (reversible), the compression ratio is worse than before.
Look at this link for more information.

Vectorial Formats


encapsulated post-script (EPS)


Drawing eXchange Format (DXF)


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