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A TIFF image comprises several million picture elements or pixels. A certain grayscale or color value is encoded for every pixel along with its exact position in the file.
The difference between TIFF and JPEG is the way in which this encoding is performed. If you have bitmap files that have to be repeatedly edited, it is best to save these in TIFF format. TIFF files store all information in uncompressed format or in compressed format without any loss.
A TIFF file stored in uncompressed format can be reduced in size significantly by LZW compression. LZW (Lempel-Ziv-Welch) compression is suitable for TIFF files. An LZW-compressed file can be read by most programs.
The file size depends on various factors, including the resolution, dimension and image depth that the file was saved in.
The resolution
defines how many pixels are present per inch (dpi = dots per inch). The higher the resolution, the better the quality. However, this also rapidly increases the size of the file.
A resolution of up to 300 dpi is normal for color images required for offset printing. A lower resolution is sufficient for other printers, e.g. laser or inkjet printers. To retain flawless results, the resolution of a scanned image of say 300 dpi is halved to 150 dpi.
No interpolation is employed in the image, as would be the case at a resolution of e.g. 200 dpi. Interpolation involves the generation of new pixels and can cause the image to lose its sharpness.
The dimension
is the extent that the image is saved in. In IsoDraw, there is a choice between the sheet size and extent of the graphic. Extent refers to the outermost coordinates of a graphic, i.e. the bounding box.
You can work with a user-defined bounding box if you plan to subsequently position the graphic in a DTP program. To do this, you create an invisible frame behind the graphic that corresponds to the frame size in the DTP program. The advantage is that the graphic no longer has to be scaled, rendering text and line thickness scaling unnecessary.
The image depth of a TIFF file
defines the amount of different colors that can be contained in a TIFF file. A line-art illustration can only contain black or white pixels, and a grayscale image can contain up to 256 different levels of gray.
Color images are limited to 256 colors (8 bits) or any of the settings up to and including 16.7 million colors (24 bits).
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24 bit color image
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8 bit color image
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Grayscale image |
Black/white line-art illustration | Increased blurring between the pixels can be seen in compression 2. In this case, the file size can be greatly reduced, however this has a detrimental effect on quality.
The compression
The compression option allows you to markedly reduce the size of the TIFF file without affecting the quality of the image. PackBits or group 3 or group 4 fax compressions are suitable for black/white images. Group 4 compression in particular produces remarkable results. Unfortunately, not all programs support this compression.
Sample black/white image:
| Compression of black/white image |
File size |
| TIFF, uncompressed |
123 KB |
| TIFF compressed with PackBits |
72 KB |
| TIFF compressed with CCITT group 3 |
41 KB |
| TIFF compressed with CCITT group 4 |
28 KB |
| TIFF compressed with LZW |
44 KB |
| TIFF compressed with LZW2 |
45 KB |
You use either LZW or LZW2 compression for grayscale or color images.
| Compression of a grayscale image |
File size |
| TIFF, uncompressed |
978 KB |
| TIFF compressed with LZW |
279 KB |
| TIFF compressed with LZW2 |
312 KB |
The grayscale option does not support PackBits, CCITT group 3 and CCITT group 4 compression.
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