Railfan Technology > B&W 8-bit vs. 16-bit

I still have hundreds of Dave England photos yet to scan, so I recently did a test of 8-bit vs. 16-bit, and 1200 ppi vs. 800 ppi. Scanning at 1200 ppi takes about 30 seconds longer, and produces a bigger file. Also, scanning 16-bit also makes a bigger file.

Here is a side-by-side comparison, along with the basic image.

I don't see any difference, especially in the smoke and clouds, where 16-bit would be an improvement over 8-bit due to more shades of gray.

Based on this direct comparison, I'll be doing 800 ppi, in the interest of time, and 8-bit in the interest of file size. [edit] I decided to use 1200ppi, to match the National Archives standard.

For anyone interested, here are the comparison layered PSD file (29.3MB), and the flattened TIF file (20.8MB).

http://utahrails.net/images/8-bit_vs_16-bit_800-ppi_vs_1200-ppi_test.psd

http://utahrails.net/images/8-bit_vs_16-bit_800-ppi_vs_1200-ppi_test.tif

Don Strack



Edited 3 time(s). Last edit at 08/18/14 08:08 by donstrack.

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The difference will depend on the photograph. If there is more info in the negative than 8 bits, then 16 bits will let you pry it out in a 16 bit editor. I'm guessing that for B&W, it's gonna be a wash. I'd love to be proved wrong on that! I use 16 bits for digi camera color shots, and I know I'm sucking more data out of the darks, and allowing the highlights not to burn out.

John.

I've always been scanning negs from 2-1/4 up @1200 dpi and 8 bit.
A friend of mine who is scanning negs for a historical society who is doing it 1200 dpi TIFF color. Makes huge files and I'm not sure it is worth the space, but he likes it.

If you scan such that you need only minimal changes in Photoshop afterwards, then it makes no difference. If you need to make significant tonal adjustments in Photoshop to contrast, brightness, shadows, clipping points, etc. after scanning then the 16-bit file will give you more tones to play with and will avoid posterization in areas with only minor tonal differences (such as the sky).

Here are the file dimensions of the four test scans.

1200ppi, 16-bit, 5725x3662, 40.9MB
1200ppi, 8-bit, 5725x3662, 20.4MB
800ppi, 16-bit, 3616x2441, 18.2MB
800ppi, 8-bit, 3616x2441, 9.1MB

I've decided on 1200ppi and 8-bits.

I agree about the consideration of using Photoshop (or other image editor) to adjust tonal changes. I try to keep them at a minimum. I have found that the Epson OEM scanning software I use does too much if I let it scan at anything other than a "raw" scan with no correction. Thus I am forced to do any needed tonal changes myself.

To keep these tonal changes at a minimum, I only adjust the pure white and pure black levels to where they start, giving the image a semblance of full tonal range. I then adjust the gray tone to bring up the shadows, but keep the highlights from blowing out. I then do a minimal adjustment of contrast.

I use FastStone more often than Photoshop because it loads much faster, and the Levels and Colors (Gamma/Contrast) are easier to access and adjust with the mouse and scroll wheel. I've compared the results after adjusting in both FastStone and Photoshop, and they appear to be identical; but using FastStone is easier to get the work done.

The difference in time is 19 seconds for an 800ppi scan, and 52 seconds for a 1200ppi scan. The final file size is in the range of the National Archives standard of 5000 pixels along the long side.

I'm not too concerned about the overall quality of scans made from these prints, mostly since they are simply railfan photos from the 1930s and 1940s, taken by non-professionals. They are all contact prints made from 2-1/4 x 4-1/2 and 3-1/4 x 5-1/2 negatives. Scanning them at 1200ppi seems to make them fully zoomable for examination of details, and they display nicely full-screen on large computer screens. I've looked at them on several various screens, including mobile devices, and the resolution is entirely acceptable. Several were used as part of an article in a recent issue of The Streamliner magazine from Union Pacific Historical Society, and I was impressed at how good they look.

Don Strack

I am not the expert in spite of scanning for 20 years. However, the more resolution or ppi should get you bigger, better prints. The higher the bit rate, the greater the playground you have to do adjustments.

Dennis Livesey
New York, NY

File size with photos is more important for manipulation speed than for storage cost. At $50 for a Terabyte of storage on a rotating hard drive, that's 5-cents for a Gigabyte, or five 40 MB photo files for just 1-cent. And it will only continue to get cheaper.

Dick Harley
(former Western Digital employee)
Laguna Beach, CA

The big difference is the information which is thrown away and lost forever. Sixteen bits saves the most information, eight bits may lose more.

It is all in the subtleties of the image and is certainly more important in color than black and white. These subtle changes are what make the image three dimensional. This is what shows a round pipe instead of a stamped piece of metal.

So the question is can you afford to throw all that information? Some old films and processing might not even record the subtleties so it is not there to throw away. If the final use is printed magazines the print screen cannot reproduce the bit depth so it is not needed. The end user needs to decide the final use and what is needed there. If the scan is for archival storage I would be hesitant to lose data account the future is just going to bring more amazing technologies to image viewing. They might not work so well with missing data.

You have a tough decision to make. For the b&w prints for the historical society use in internet searching and magazine publication I think the higher resolution 8 bit scans is probably a good standard. If the originals are going to be scattered or lost afterwards then I think I would scan for the highest resolution and bit rate the original can stand with the equipment and time available.

And thank you for taking your time and skills to make these images more widely and easily available.

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