TIFF

The following demonstrates how to create 24 bit colour RGB TIFF (Tagged Image FIle Format) files. That is, how to create images from your own software that can be then opened and manipulated with image handling software, for example: GIMP, PhotoShop, etc. Given this aim, this document illustrates the "minimal" requirements necessary to create a TIFF file, it does not provide enough information for writing a TIFF file reader. For more information on the full TIFF specification the following postscript and pdf files describe the TIFF version 6. The first 8 bytes forms the header . The first two bytes of which is either "II" for little endian byte ordering or "MM" for big endian byte ordering. In what follows we'll be assuming big endian ordering. Note: any true TIFF reading software is supposed to be handle both types. The next two bytes of the header should be 0 and 42dec (2ahex). The remaining 4 bytes of the header is the offset from the start of the file to the first "Image File Directory" (IFD), this normally follows the image data it applies to. In the example below there is only one image and one IFD. / Each IFD entry consists of 12 bytes. The first two bytes identifies the tag type (as in Tagged Image File Format). The next two bytes are the field type (byte, ASCII, short int, long int, ...). The next four bytes indicate the number of values. The last four bytes is either the value itself or an offset to the values. The following is an example using the TIFF file shown on the right, namely a black image with a single white pixel at the top left and the bottom right position. The image is 100 pixels wide by 200 pixels high. A hex dump is given below along with matching pointers and locations marked in matching colours, these colours further match the appropriate parts of the source code gievn later. The tags are underlined. TIFF RGB images should always have a contiguous (RGBRGBRGB ...) not planar (RRR..RGGG..GBBB..B) format. While the header allows you to specify planar, it is not well supported. For 16-bit data, be aware that most TIFF viewers ignore the maximum and minimum values and assume your data is scaled from 0 to 65535 (You can test this with my example). For 16-bit data, it is important that the endian is set correctly. For data with only one component (e.g. grayscale or black and white) you encode min, max, bits per sample directly in the tag, for RGB data the tag provides a pointer to the address for those values. The following example are an adaption of the above with the following additional features. Example that copies an arcane lossless JPEG format that is popular with medical imaging to TIFF (my own library).