Why Your Fax Confirmation Might Appear to Be Low Quality

When you upload a crisp, high-resolution document to PayPerFax – whether it’s a 300 dpi PDF, a high-quality scan, or a document created in Word – and receive a fax confirmation email with a PDF that looks fuzzy or pixelated, it’s natural to worry whether your recipient will be able to read it.

The short answer: Despite the lower resolution you see in your confirmation, your recipient will be able to read what they need in 99% of cases.

Why it looks different:

1. Fax technology has a maximum resolution of 204×196 dpi (“fine” resolution), which is likely significantly lower than your original document. This is a limitation of fax technology itself, not of PayPerFax.
2. Fax machines only understand pure black and white – no greys, no colors. When PayPerFax receives your document, it needs to convert it to a format that the recipient’s fax machine is capable of receiving. This conversion drops the resolution and converts all greys to patterns of black and white pixels.
3. The PDF attached to your confirmation email shows exactly what was transmitted to the recipient’s fax machine, pixel-to-pixel. But when you view this PDF on your screen, the lower fax resolution looks more noticeable than it will when the recipient prints it.

Understanding Fax Resolution

Compare typical document resolutions:

• Fax transmission: 204×196 dpi (used by all fax machines)
• Your uploaded PDF: Often 300 dpi or higher
• Scanned documents: Usually 200-600 dpi
• Screen displays: 96-150 dpi

PayPerFax always sends at “fine” resolution (204×196 dpi), which is the highest resolution supported by standard fax technology. “Standard” resolution (204×98 dpi) is even lower, but we never use it.

These standards remain unchanged because fax machines worldwide must communicate using the same language – a machine in Tokyo needs to communicate perfectly with one in Buenos Aires.

Converting to Black and White

Since fax machines only understand pure black or pure white, every shade of grey in your document needs to be converted (through a process called “dithering”). There are different methods for doing this conversion, each with trade-offs.

PayPerFax defaults to a method optimized for images and mixed content. This ensures that scanned documents, signatures, and photographs transmit clearly. Text may look slightly less sharp than it would with a text-only method, but the trade-off allows both text and images to remain readable in the same document.

Technical Details: Dithering Methods

The conversion from greyscale to pure black and white is called “dithering.” Different dithering algorithms make different trade-offs:

• Error diffusion dithering: Spreads conversion errors across neighboring pixels, creating natural-looking patterns that work well for photographs and complex graphics
• Threshold dithering: Simple conversion where pixels above a brightness threshold become white and below become black, producing sharp text but poor image quality
• Ordered dithering: Uses predefined patterns to simulate grey shades, balancing between text and image quality

PayPerFax defaults to error diffusion because most documents contain both text and visual elements. This produces results that work acceptably for both, even if neither looks perfect at high magnification.

The choice affects how readable your document appears but rarely affects whether it’s functionally usable by the recipient.

Real-World Readability

Faxes that look pixelated when zoomed on your screen typically read fine when printed or viewed at normal size.

Common scenarios:

• Word processing documents: Text remains readable despite looking less sharp than the original
• Scanned forms: Handwriting and printed text come through clearly
• Documents with light backgrounds: Grey scanning artifacts convert to visible patterns but don’t obscure text
• Mixed content pages: Both text and images remain identifiable

If you can read the text in your confirmation PDF without significant eye strain, your recipient will have no trouble with it.

When Lower Quality Becomes a Problem

Most recipients accept faxes at this resolution without issue. However, some situations require different handling:

• Very small text that becomes illegible after conversion
• Light grey text that disappears against light backgrounds
• Detailed graphics with fine lines that merge together
• Poor quality scans that were already borderline readable

If your recipient tells you they can’t read your fax, we can resubmit it using a different conversion method at no extra charge. Different methods work better for specific situations – some optimize for plain text, others handle light backgrounds better, and some work well with unusual document formatting.

Contact us if your recipient reports readability problems.

Why This Limitation Exists

Fax technology dates to the 1960s and became standardized in the 1980s. The resolution and black-and-white limitations reflect the telephone line limitations available at that time.

Modern online fax services like PayPerFax can’t bypass these limitations when communicating with traditional fax machines, which still handle the majority of fax traffic.

Technical Details: Fax Resolution Standards

The International Telecommunication Union (ITU) defines fax standards:

T.4 (Group 3): The standard used by nearly all fax machines

• Standard resolution: 203×98 dpi (horizontal×vertical)
• Fine resolution: 203×196 dpi
• Superfine resolution: 203×391 dpi (rarely supported)

Why the asymmetric resolution? Early fax machines scanned horizontally at higher resolution than vertically to reduce transmission time. Vertical resolution could be lower because text remains readable with fewer scan lines.

Why only black and white? Greyscale or color faxing requires significantly more bandwidth. A greyscale fax with 16 shades of grey would take 4 times longer to transmit. At typical transmission speeds of 14.4 kbps, this would make faxing impractically slow.

The binary (black or white) approach keeps transmission times reasonable over standard phone lines.

Summary

• Your confirmation PDF shows exactly what transmitted to the recipient
• Fax resolution (204×196 dpi, black and white only) is lower than modern document formats
• This is a limitation of fax technology, not PayPerFax
• Documents that look pixelated in confirmations are usually perfectly readable to recipients
• If readability becomes an issue, we can reprocess and resend at no charge using different conversion settings

The fuzzy appearance of your confirmation PDF doesn’t indicate a problem – it shows normal fax quality that recipients process successfully thousands of times daily.