8 bit vs 16 bit Tiffs

[Brendon Fewel]

Help me get this straight please. How much information is lost if I save my raw files (from a Canon s45) as 8 bit tiff vs 16 bit tiff (so I can edit them in PS)? What difference is there; will I miss it? Should I worry about it?

Anyone know? Thanks!

Brendon

[Chris Cox]

That depends entirely on the image in question.

If you had some shadow detail or hilight detail that you wanted to bring out later (by adjustments of filters) - then you could lose quite a bit.

If you have the RAW file around for archival purposes, and the image is properly exposed -- then you may get by with 8 bits/channel.

[Brendon Fewel]

If you can loose so much information, why does PS only let you work with 8 bit tiff images? I thought that people who used PS were heavy into photography; why would they use a program that doesn't let you use the highest quality images?

[Jake Hannam]

I think it is for a couple of reasons. First, many of the effects do not work with 16-bit files (Adobe should be able to fix this but has not so far). Second, 16-bit files are much larger than 8-bit files so they are harder to manipulate. They take up much more hard disk space and memory due to the additional information they include. Third, as Chris Cox says, it depends entirely on the image in question. Many times the file-size tradeoff in terms of memory and disk space used are not worth it. However, with hard drives and memory being so reasonable these days, argument #3 is quickly becoming less important.

Jake

[dennis johnson]

Well, think about it. How many devices, including the monitor you're using right now, can utilize or display more than the number of colors that can be described by 8-bit color?

You ask, "...why does PS only let you work with 8 bit tiff images?" But Photoshop does give you the ability to edit and manipulate 16-bit images, including 16-bit TIF, so I don't understand your complaint. Use the bit depth that you find more convenient or applicable to your purposes, and others will use what they need.

The world is wide.

[Brendon Fewel]

Everthing you've said makes sence, except that I guess that my missing piece of knowlege is how many colors can be described by 8-bit color?

And I didn't mean to make my last comment sound like a complaint, sorry about that. I phrased it in a chalenging way that I hoped would cause someone to fill in my knowlege gaps. (such as "What are you talking about? 8 bit is PLENTY of colors because...") Thanks for your help!

[YrbkMgr]

In 99.99% of the cases, your output devices (monitor, printer, etc) cannot present a discernable difference between the number of colors produced by 16 bit data and 8 bit data. In other words, you won't see it, in general.

So why have it? There are two reasons that I can think of.

First, 16 bit data contains more information. If you manipulate an image in 16 bit, then convert to 8 bit, the histogram remains relatively smooth (no drop outs). Who cares? Some do - some ascribe to the theory (by necessity or desire) that they want to work with as pure a data set as is possible. Will they see a difference? In most circumstances, no, but the data is about as pure as they can get and that is satisfying. Especially for archivists.

The other reason is that for SOME images one *may* be able to see the differences post manipulation. They will be very subtle, but a trained eye may be able to detect them. It's rare that this happens, but it happens.

So in consideration of that, think of the processing power required to use a filter on 8 bit v. 16 bit data - it's an order of magnitude higher. So the question is, for what? To date, it appears that Adobe is of the mind that the performance/benefit ratio isn't worth it.

Whether that's actually true or not, seems, from what I've read, to be an individual perspective rather than an industry wide one.

Peace,
Tony

[dave milbut]

<http://www.ledet.com/margulis/ACT_postings/ColorCorrection/ACT-8-bit-16-bit.htm>

[Chris Cox]

Dave - I tend to regard that link as useless. They didn't do very good testing. (And Dan has an obvious agenda, as usual).

[dave milbut]

chris, i didn't read it all the way through, but i figured it would at least help a beginner. thanks for the heads up though.

dave

[Eric Purkalitis]

Brendon,

you might want to look at something like Asiva <http://www.asiva.com/photo.html> if you want to edit only in 16-bit. I dont quite feel the need for it. I figure I can bring out the detail I want with levels and curves and then switch to 8-bit to do my editing. There arent many ways to output which will take advantage of a pure 16-bit image (the printing gamut is usally smaller than 8-bit).

Ive seen <http://www.inksupply.com/index.cfm?source=html/quadtone.html> for 4 and 6 color printers which expand the b&w printing gamut (sorta ala Ansel Adams effect). I've been thinking about trying it, I'm still not convinced even that would need 16-bit.

Hmmm, anyone else noticing the apostrophes disappearing in their posts?