8-Bit, 24-Bit, 48-Bit, 64-Bit: Bit Depth Explained for Scans

Scanner boxes and file settings are full of numbers: 8-bit, 16-bit, 24-bit, 48-bit, even 64-bit. They sound like a ladder of quality, but some of them describe the same thing in different ways. Here is what they actually mean.

What a “Bit” Is Doing

Every pixel in a scan stores a brightness value for red, green and blue. Bit depth is how many steps each of those values can have. More bits means finer steps between dark and light.

• 8 bits give 256 steps.
• 16 bits give 65,536 steps.

Why the Numbers Are Confusing

Sometimes the number describes one colour, and sometimes all three added together:

So “24-bit” and “8-bit” usually mean the same thing, and so do “48-bit” and “16-bit”. Black-and-white scans have only one channel, so an 8-bit or 16-bit greyscale scan is exactly that.

The 64-bit files some film scanning software creates are 48-bit colour with the scanner’s infrared layer stored alongside. That extra layer is what allows dust and scratch removal to be done later, rather than at the moment of scanning.

Can You See the Difference?

Usually not, at first. Almost every screen, phone and printer works with 8 bits per colour, and 16.7 million colours are more than the eye can separate in a normal photo. A good 24-bit scan and a 48-bit scan of the same print look the same side by side.

The difference appears when you edit. Brightening a dark photo, rescuing a faded print or correcting a strong colour cast stretches those steps apart. With only 256 steps, smooth areas such as skies, walls and skin can break into visible bands. With 65,536 steps there is plenty in reserve, and the result stays smooth.

Where Bit Depth Matters Most

• Faded and very dark originals, which need big corrections.
• Negatives and slides, where the scanner has to capture a wide range from the densest shadows to the brightest highlights.
• Restoration work, where a photo may be adjusted many times.
• Raw scans, which are often 16 bits per colour so that all the correction can be done later.

Bit Depth and File Formats

This is one of the main reasons keen photographers ask for TIFF or RAW files. See our guide to JPEG, TIFF and RAW for more.

The Cost: File Size

More bits means bigger files. For a 6×4 print scanned at 600dpi, before any compression:

A 35mm slide or negative scanned at 3600dpi is about 5,100 by 3,400 pixels, so its files are larger: about 52MB as a standard (24-bit) TIFF and about 104MB as a high-detail (48-bit) TIFF.

A Note on Scanner Marketing

A scanner advertised as “48-bit” can store 16 bits per colour, but its sensor may really capture 12 or 14 bits, with the rest filled in. That is normal and still gives far more room than 8 bits. The quality of the scanner’s optics and sensor matters much more than the number on the box.

Which Depth Is Right for You?

• Choose Standard (24-bit JPEG): If you want to view, share on WhatsApp, post to social media, or print standard copies. This is perfect for 95% of family archives.
• Choose Archive-Grade (48-bit TIFF): If you plan to do heavy digital restoration, significantly enlarge the photos, or want an uncompressed “master copy” kept safe for future generations.

With every SilverFrame order you get a finished JPEG of every scan. TIFF files are an optional extra, 10p a picture on top of the scanning price. You can choose a standard TIFF (8 bits per colour) for any photo, slide or negative, or a high-detail TIFF (16 bits per colour) for slides and negatives at the same price. Prints come off our photo scanner at 8 bits per colour, so a 16-bit TIFF of a print would be bigger but no better.