Rohman
TIFF is what scanners, fax servers and document-imaging systems write when nobody asks them to write anything else. Medical records come out of the archive as TIFF. A law firm's e-fax inbox saves every incoming fax as TIFF. Then someone needs to email one, or upload it to a portal that takes PDF and nothing else, and discovers that their phone can't preview it and their browser just downloads it.
Converting is easy. Converting so the PDF comes out at the right page size and a sensible file size takes a little more knowledge about what's inside the TIFF, and while writing this I found our own converter getting the first part wrong.
Quick answer: To convert a TIFF to PDF, open TIFF to PDF, drop in your .tif or .tiff files, and every page of every file appears in one grid. Drag them into order, leave Page Size on Fit to Image and Compression on Lossless for scans and faxes, then convert. You get one PDF. Use Lossy (JPEG) only for color photos: on a black-and-white fax it makes the file several times bigger.
A TIFF Can Hold a Whole Document
Most image formats hold one picture. TIFF holds a list of them. Each page is an entry the spec calls an Image File Directory (IFD), and a 30-page scan saved as TIFF is usually one file with 30 IFDs, not 30 files. That's why a scanned contract arrives as a single .tif that most image viewers show as one page: they read the first IFD and stop.
A good converter reads them all. TIFF to PDF decodes every page in every file you add, numbers them (scan.tif · 3/30), and lays them out together, so combining several TIFF files into one PDF is the same action as converting one. If a batch of faxes came in out of order, drag pages around before you convert. Pages from different files can be interleaved freely.
Faxes Have Non-Square Pixels
This is the part that caught us out.
A TIFF records its resolution in the file: two tags for pixels per inch (or per centimeter) across and down. A letter page scanned at 200 DPI is 1700 by 2200 pixels with both tags set to 200, and the only correct PDF page for it is 8.5 by 11 inches.
Fax is stranger. The fax standard (ITU-T T.4) scans 1,728 pixels across a 215 mm line, about 204 per inch, but in standard mode it only takes 98 lines per inch down the page. Fine mode doubles that to 196. So a standard-mode fax page is roughly 1728 by 1100 pixels, and each pixel is twice as tall as it is wide. Show it pixel for pixel and the page comes out squashed to half its height, with letters twice as wide as they should be.
Until this week, our converter ignored both tags. Fit to Image assumed every pixel was 1/96 of an inch, which is right for a screenshot and wrong for almost every scan. I ran a test file through it: the 200 DPI letter scan became a 17.7 by 22.9 inch PDF page, and the standard fax became a landscape page half as tall as it should be. It looked fine on screen, because a viewer zooms to fit, and it would have printed at the wrong size or been rejected by any portal that checks page dimensions.
Fit to Image now reads the resolution tags, in inches or centimeters, and honours pixels that aren't square. The same two files come out as a letter page and an 8.47 by 11.22 inch fax page, which is what the fax machine scanned. A TIFF with no resolution tags still falls back to 96 pixels per inch. If your scanner leaves the tags out, or writes a placeholder like 72, pick A4 or Letter instead and the page will be the size you expect whatever the tags say.
What Happens to the Compression
TIFF isn't really one format. It's a container for a dozen compression schemes, and which one your file uses decides what the right PDF settings are.
- CCITT Group 4 is what black-and-white scans and faxes use. It encodes only where the black runs start and stop, one bit per pixel, so a page of text is often 20 KB.
- LZW, Deflate and PackBits are lossless general-purpose schemes, common for grayscale and color scans.
- JPEG-in-TIFF shows up in photo workflows and some scanners' "compact" modes.
- Uncompressed is what older software writes, and it's enormous.
TIFF to PDF reads all of these. It doesn't copy them into the PDF untouched, though. Every page is decoded to pixels and compressed again, with one of two choices:
Lossless stores the pixels with Flate, the same lossless compression PNG uses. Every pixel survives.
Lossy (JPEG) re-encodes each page as a JPEG at the quality you set (92% by default).
I measured both against four test files, driving the real tool in a browser:
| What you're converting | TIFF size | Lossless PDF | Lossy PDF |
|---|---|---|---|
| 3-page fax, Group 4, 200 DPI | 65 KB | 167 KB | 966 KB |
| 1 grayscale scanned page, LZW | 236 KB | 200 KB | 243 KB |
| 1 color photo, LZW, 2400 px wide | 5.0 MB | 7.9 MB | 264 KB |
The fax row is the one to remember. JPEG is built for smooth tones, and a fax is the opposite: hard black edges on white. Feed it a fax and you get a file almost six times bigger than lossless, with gray fuzz around every letter. For the color photo, JPEG is 30 times smaller than lossless and you won't see the difference.
The other number worth admitting: lossless output for the fax is about 2.6 times the size of the Group 4 original. PDF can hold Group 4 data directly, and some converters copy it across byte for byte. libtiff's command-line tiff2pdf does this for single-strip Group 4 files, which is how most faxes are written. If you convert thousands of faxes for an archive and storage is the constraint, that's the better tool for the job. For a few files you're about to email, 55 KB a page is fine.
Two rules cover almost every case:
- Black-and-white scans, faxes, and anything with text or line drawings: Lossless.
- Color photos and color scans of photographs: Lossy, quality 85–92%.
A grayscale document scan sits in between. Lossless was a little smaller than lossy in my test and keeps text sharp, so start there.
How to Convert TIFF to PDF in Your Browser
- Open TIFF to PDF and drop in one or more
.tifor.tifffiles. Multi-page files expand automatically. - Check the page grid. Each thumbnail shows its file, page number and pixel size. Drag pages to reorder them, or remove any you don't need.
- Choose a page size. Fit to Image uses the size the scanner recorded. A4 or Letter puts every page on standard paper, scaled to fit, which is the safe choice when pages came from different sources. Advanced Options adds orientation (auto, portrait, landscape) and a margin of up to an inch.
- Choose compression using the two rules above.
- Convert, name the file, and download it.
Nothing leaves your device while this happens. The TIFF decoder runs in your browser tab, which matters when the scans are patient records, signed contracts or someone's tax documents. Here's why every OxygenPDF tool works that way.
After You Convert
A scanned PDF is still a picture of text, so you can't search it or copy from it. Run it through OCR PDF to add a hidden text layer; making a scanned PDF searchable covers the details.
If the PDF is too big for an email or upload limit, Compress PDF can shrink color and grayscale pages further. For a document that has to stay readable for decades, convert it to PDF/A with PDF to PDF/A; what PDF/A is explains which version to pick.
Going the other way, for a system that only accepts TIFF, PDF to TIFF writes a multi-page TIFF from any PDF. And if your images are JPG or PNG rather than TIFF, JPG to PDF does the same job for them.
Frequently Asked Questions
How do I convert a multi-page TIFF to PDF?
Drop the file into TIFF to PDF. Every page in the TIFF is read automatically and becomes one page of the PDF, in order. You don't need to split the TIFF first.
How do I combine several TIFF files into one PDF?
Add all the files at once, or add more after the first. Their pages appear in a single grid that you can drag into any order, and converting produces one PDF with all of them.
Is TIF the same as TIFF?
Yes. .tif and .tiff are two spellings of the same format's extension, a leftover from systems that only allowed three-letter extensions. Both convert the same way.
Why is my converted PDF page the wrong size?
Usually because the converter ignored the resolution stored in the TIFF, or the scanner wrote none. TIFF to PDF reads it now. If a file has no resolution tags, choose A4 or Letter to put each page on standard paper.
Does converting TIFF to PDF lose quality?
Not in Lossless mode, which keeps every pixel. Lossy mode re-encodes pages as JPEG, which is fine for photos and bad for black-and-white text, where it adds gray fuzz and makes the file bigger.
Can I convert a fax TIFF to PDF?
Yes. Group 3 and Group 4 fax compression are both supported, and standard-resolution faxes keep their correct page height. Use Lossless to keep the file small.
Got a stack of scans that won't open anywhere? Convert your TIFF to PDF in your browser, at the size they were scanned.
