CopiaFacts provides many features to optimize the quality and legibility of faxed documents, and at the same time to maximize the speed of transmission. This topic outlines the best ways to achieve this goal. See also the links at the end of this topic.
Faxing became widespread in the 1970s, optimized for transmitting black text on white paper. The image compression used for fax expects to see small runs of black pixels separated by longer runs of white pixels, and compresses each of these extremely well. All other image types 'compress' very poorly, and usually end up sending more data than the uncompressed image file.
The best way to ensure that the recipient sees high quality documents, and that you can send them quickly, is to start with crisp, text-only original documents. If you know that this is what your users will normally be sending, you can ignore this topic and use the default settings.
If you have no control over what documents are sent, there are steps you can take to improve quality and speed. However there may need to be some compromises: settings to improve some document types may make others worse. CopiaFacts allows some settings to be made at a user or job level, to affect the specific types of document only.
The types of optimization required will vary depending on what types of document you are aiming to improve.
Color and Grayscale Documents
| Dithering | Since faxes only transmit black and white pixels, all color and grayscale text and background is first converted to a close pattern of black and white pixels. This operation is known as dithering, and can result in very large faxes. A blank white page fax would be only about 500 bytes; change the original page to light yellow or light gray, and the fax size jumps to 350 kilobytes, and for a dark page about 1.5 megabytes. The same ratios apply when only a part of the original document has the colored background. |
| | When only the text is colored, the size increase is less marked. However the result is shaded, fuzzy characters, so for example bright red text intended to stand out in the document becomes gray and easy to miss in the surrounding black text. Black text on a non-white background also becomes fuzzy as background pixels attach to the letters. |
| | The image options DITHER keywords can be used to change the algorithm for dithering. Changing the difhering method may improve the appearance slightly but makes little difference to the document size. |
| Fixing backgrounds | The easiest way to fix light-colored backgrounds is to change them to be white, using the BGCOLOR or LIGHT image options keywords. These change brighter colors to white before rasterization. The first is a fairly safe option to use with all text documents, because it only operates when a large block of the same color is detected; with the second, if the document contains a picture, its colors will be distorted. |
| | An alternative way to remove a background is to lighten the whole document using the BRIGHTNESS or GAMMA image options keywords. The CONTRAST keyword may also help in some cases. |
Unsharp or Degraded Documents
| Fixing poor scans | Documents which are presented as scanner output may have already acquired some loss of sharpness; photographed documents are typically degraded by partial shadows or reflections. Some of this can be improved by the image options keywords EDGE and SHARPEN, and some of the options suggested for background colors may also help. |
| Speckle | Speckle (small dark dots) is often a problem with poor-quality scans, and especially with JPEG documents, where every sharp change of color can be seen, when enlarged, to have had its edge 'softened'. The DESPECKLE image option can make considerable improvement in such images. However it is necessary to experiment and avoid too aggressive a setting, for fear of removing the dots on letters i and j in text blocks. |
| Photographs | Documents photographed for faxing are usually difficult to optimize unless care is exercised when the photograph is taken and processed. Encourage the use of PNG and TIFF to make the original document, and avoid JPEG if possible. The CONTRAST image option will try to balance the light and dark areas. |
Transmission Resolution
| High resolution | High or 'fine' Resolution Faxes are normally 204 dpi horizontal resolution and 196 dpi vertical resolution, but sometimes you will receive faxes 200x200. This is the highest widely supported resolution; although higher resolutions (300 or 400) are part of the fax standard their use is specialized and not often encountered. Use High Resolution to prioritize quality over transmission time. |
| Low resolution | Low Resolution Faxes are typically 204 dpi horizontal resolution and 98 dpi vertical resolution. Many systems simply merge pairs of alternate scan lines into one on transmission and duplicate every scan line of incoming low resolution faxes. The fax then takes half the time to transmit, and looks a little fuzzier on receipt. In some small-size fonts, a capital H may lose its horizontal bar. The image option keyword LOWRESMS does this. Low resolution faxes are noticeably lower quality than High resolution. |
| Enhanced Low Res. | CopiaFacts can convert documents to low-resolution TIF by adjusting the dithering pattern so each output scan line gets elements from its neighbours instead of being merged together. This can make a better quality fax overall than simply merging a black pixel in either of a pair of scan lines into the single output scan line, at a cost of a very slightly larger file. The image option keyword LOWRES does this. |
Illustrated examples of the effect on document quality of these resolution settings can be found in the image options keywords topic.
Image Encoding (Compression)
 | The choice of Fax Encoding Method does not affect image quality. It is mentioned here only for completeness. All the fax encoding/compression methods are loss-less, and affect only the size of the TIF and thus the time taken to transmit it. CopiaFacts normally defaults to MMR encoding. |
Modified Huffman (MH) is the least efficient encoding, producing the largest files. It compresses each scan line at a time. It is also known as "Group 3" encoding and is supported by all G3 fax devices.
Modified Read (MR) is a two-dimensional encoding so is more efficient when scan lines are repeated. It is supported by most G3 fax devices and is also named "ITU.T4" or "CCITT.T4". It encodes to create smaller files than MH.
Modified Modified Read (MMR) is an extended two-dimensional encoding used in G4 fax devices, which encodes to smaller files than MR. It is also named ITU.T6 or CCITT.T6.
Applying the Image Options
| Experimenting | It is essential to experiment with loading PDF, HTML and image documents into FFVIEWER to see how they will be converted. You can then open the image options editor to tweak the settings. As the document is reloaded after each settings change the size of the file is displayed, which of course correlates with t transmission time. Sometimes the improvement in quality cannot be paired with a reduced transmission time. |
| Implementing | The goal should be to create sets of image options which work well for specific classes of documents. Some may be of general use and can be made the default (option 0). Others may be selected in a specific user profile (USR) or template (FST), or in owner or job properties (UJP) for Job administration users. |
| Multiple Option Sets | CopiaFacts includes a TRY image option which allows multiple option sets to be specified, and the document conversion is then repeated if the first attempt produces too large a file. We recommend that this option is not selected until the separate option sets have been tested and verified in production, and only if no more straightforward way can be found to select the best conversion. Again, it is possible to construct an option set which creates a very small output file, by accidentally eliminating much of the document content. |
See also
