The image formats
This part of the physical specifications clarifies the use of TIFF as format for images which are included in Formex instances (INCL.ELEMENT).
The specifications are based on the international standard TIFF (Tagged Image File Format), version 6.0, described in the document
The TIFF standard
The TIFF 6.0 specifications are composed of two parts. The first one describes the kernel of the standard. It has to be fulfilled by any tool which is said to be TIFF compatible. The second part contains extensions which have been added for special purposes. Therefore they may not be available in all tools.
The kernel describes four image types:
- bilevel encoding, black and white: the two formats TIF_G3 and TIF_G4 only allow the encoding of black and white images;
- encoding of different grey scales (16 or 256 levels);
- encoding of colours with a palette included in the TIFF file itself; in that case the pixels reference the entries of the palette;
- encoding of colours according to the RGB methodology (Red - Green - Blue).
All tools which are compliant to TIFF 6.0 have to handle these four formats.
The specifications of compression algorithms within the kernel of the standard are limited. For images in black and white, two methods are allowed: TIF_G3 and PackBits. The other formats only support the method PackBits.
The format TIF_G4 was introduced as recommendation by CCITT for the encoding of fax transmissions. Its only interest consists in the higher rates of compression. As this format is not part of the kernel, it is not supported by all tools on the market.
Images within Formex deliveries
Within the Formex deliveries the Publications Office only accepts TIFF images which can be displayed by Quick View and Imaging and be inserted into Word 97 documents.
For these reasons, only the following formats will be accepted by the Publications Office:
- black and white images with TIF_G3 or PackBits compression; the photometric interpretation has to be set to 'min-is-white' (in general, this is the default value of this tag);
- images with different grey scales, without any compression;
- images with RGB colour encoding, without any compression.
The resolution has to be set to 400 dpi.
For compatibility and legal reasons, all extensions of the standard are forbidden.
Control of the image formats
The TIFF images have to be controlled by means of the library LIB TIFF V3.4 which is available from the Internet site
The images have to be recognized by the tool TIFFINFO. They have to follow one of the above-mentioned formats as specified by the kernel.