8-bit vs 16-bit - we know which is better - but what's the point?

[geoffchalcraft]

Not quite the usual Raw vs Jpg argument (which I would hope has been settled by now)..... but I've been in a position when explaining to photo club members about that argument. I've got them to understand the benefits of shooting Raw..... but there's a sticking point, which I'm at a loss to cover......

The point with a Raw shot is that it gives you the full capability of your camera in one file.... the full pixel count, the full size and the full gamut of colours - because, generally, a DSLR will give you a 12- or 14-bit Raw file, giving Trillions of colours. As per this CiC tutorial, among others. So far so good.

Then it comes to deciding how to open the file once it's been 'converted' into an editable file. To keep the full quality of the image, Adobe Camera Raw (and other software) gives you the option of opening in 8-bit or 16-bit. However, try editing the image in Photoshop or PS Elements from that (beyond the basics of re-sizing, cropping etc) and things get difficult..... layers, for example, will not work.

But OK, let's say our image didn't even need further editing.... perhaps a crop or little bit of re-sizing to suit our printer. Send the file to the printer and (as I understand it) it's extremely unlikely that even the best quality printers can actually manage anything better than 8-bit, and it's usually more like 6-bit or less. (No idea about commercial printers).

So, if you're going to print at home, is there any point at all in using the full bit-depth provided by the camera?

[Zone XI]

This is a big subject, but I have a few comments on some of your queries. When I use the RAW processor (Lightroom in my case) then edit an image in Photoshop I use the full 16-bits to get the benefit of my 5d Mk2 having 14-bits. Layers work in Photoshop (CS5) with a 16-bit image. Some filters (artistic, brush strokes, distort, pixelate, sketch & texture) do not work with 16-bit images so if you wanted to use those, you'd have to convert to 8-bits first.

The main reason for using the full 16-bits through your workflow is when you do any post-processing, adjusting the exposure, contrast, curves, shadow detail is to avoid banding (posterisation). With only 8-bits, you have 256 levels, pure white being 255, one stop lower than that is 127, so the values from 128-255 contain the details in the very white whites.
One stop down from that 64-127 contain the light grey details.
One stop lower 32-126 for darker greys.
One stop lower ... you get the point.
So the details in the dark blacks might have only a few levels, when you start to move these around, you'll see obvious posterisation. With 16-bit images you'll get far more tones in the deep blacks.

Once you've finished post-processing, the printer profile should ensure that you get the best mapping from your final toning to an acceptable print. Hope that helps.

regards, Les
www.zone-xi.com

[geoffchalcraft]

Wow! That was quick! All understood.... I'm not a user of CS5 and, though I have Lightroom, I need to upgrade my computer to make it run at an acceptable speed, so I haven't learned much from it, so I'm still using an old(ish) version of PS Elements. I'd asked on another forum some time ago and it appeared that CS4 had a big problem with 16-bit and that convinced me I wasn't going to gain much from CS.

Anyway, you've re-assured me about 16-bit and now you've convinced me to ....
a. wait until I upgrade the hardware (in the near future) and use Lightroom properly, and/or,
b. wait until I upgrade the hardware and get CS5!
(I may do both!)

Looking forward to some quality editing and better prints!

Thanks for the prompt reply and comprehensive advice..... I only joined the Forum today - I'm going to like it!

Geoff

[Simon Garrett]

I agree with Les, and one other factor.

Many edit operations result in fractional numbers. Say an R, G or B value comes out of a process at a value of 99.5 (out of 255 for 8 bits). That gets rounded to 99 or 100 - a 0.5% error. Every calculation - alteration to brightness, contrast, sharpness, tone curve... leads to a potential 0.5 (out of a maximum of 255) rounding error.

In 16 bits, the equivalent value to 100 is 25,600. So a rounding error or 0.5 would be around 0.02%. Of course, when you print or display on a monitor then it gets crunched down to 8 bits anyway. But if you do all the editing in 16 bits, then most of the calculations are much more precise, and the bigger rounding error occurs only once, when you convert to 8 bits.

[Zone XI]

Hi Geoff,

I only joined the forum today too and I like it already!
Glad to be of assistance, good luck with the upgrades.

[geoffchalcraft]

Thanks Les.

Simon..... it's that 'crunched down to 8 bits anyway' that still troubles me! But, as Les says ("Sez Les"?), we can only do our best with a correct printer and paper profile.
I'm back in the UK once I sell the house here in Canada.... almost definitely to Sussex. Probably joining at least one photo club (or try them out), then I'll see about having a go at LRPS. (I'm not in the RPS yet, not a lot of point here).

Geoff

[Sonic4Spuds]

I feel that the mention of the comming capabilitys of GIMP in this area should be made. The next version, which should reach final release by sometime in January, will support processing in up to 32 bit color(all of the operations ported to the new GEGL framework will work always in 32 bit float). The 3.0 release will be completely ported to the GEGL archatecture.

-Sonic

[Colin Southern]

Hi Geoff,

To put it another way ...

There are times where a 16 bit workflow may give a better result, but there are few occasions where using an 8 bit workflow is an advantage (assuming one has a PC that's capable enough of handling the 16 bit files - which are twice the size - without performance issues). Once any "heavy editing" is complete, it's safe to convert the image to 8 bit.

Personally, as PC performance and storage requirements aren't an issue, I generally just work in 16 bit all the time - but if I have to move a file electronically or keep the size down for some reason - then I have little hesitation in converting it to 8 bit.

In the vast majority of cases most folks probably won't get bitten in the bum too badly by using 8 bit though.

[geoffchalcraft]

Thanks for the information about GIMP, Sonic.... I've given GIMP a few tries in the past but, while I'm aware that it's every bit as capable as Photoshop, having learned most of my editing 'the Adobe way', I find GIMP's methods a tad confusing. Still, I'll give it another go.

Colin, thanks for that. I have to admit, though, that I can't quite see how editing in 16-bit and then reverting to 8-bit is going to work. For example, if I did some 'heavy editing' in 16-bit - perhaps some severe Levels editing, which would have made for some 'stepping' or slight posterisation if done in 8-bits - then dropped from 16-bit to 8-bit, haven't I defeated the object? Wouldn't the image become posterised in those areas with very smooth transitions between colours?

In the end, as a quality, large print is my 'goal', until we can get printers that deliver 16-bits, enabling a 16-bit workflow throughout, I would think it best to go with the suggestion of Les (Zone-xi, above), which is to just do the best I can in 16-bit and aim for the best print with the correct profiles.

Good Forum this!

Rgds, Geoff

[Colin Southern]

Colin, thanks for that. I have to admit, though, that I can't quite see how editing in 16-bit and then reverting to 8-bit is going to work. For example, if I did some 'heavy editing' in 16-bit - perhaps some severe Levels editing, which would have made for some 'stepping' or slight posterisation if done in 8-bits - then dropped from 16-bit to 8-bit, haven't I defeated the object? Wouldn't the image become posterised in those areas with very smooth transitions between colours?

In the end, as a quality, large print is my 'goal', until we can get printers that deliver 16-bits, enabling a 16-bit workflow throughout, I would think it best to go with the suggestion of Les (Zone-xi, above), which is to just do the best I can in 16-bit and aim for the best print with the correct profiles.

Hi Geoff,

In a word, No - the advantage of 16 bit is ONLY in the image manipulation stage, so that you don't get rounding errors as tonal ranges are stretched and compressed. Once that phase is over (and assuming that you subsequently won't have to make more of them) then dropping back to 8 bit doesn't make ANY difference.

The reason for that is that is the 16 bit value is converted to the closest 8 bit value one last time, and at that stage there can only be "1/2 a bit" of rounding error". 8 Bits supports up to 256 levels, and our eyes can only differentiate up to about 200 levels on a monitor - so this final conversion is indistinguishable to us.

Basically, all we're trying to do is prevent rounding errors compounding on one another during the manipulation phase.

Does that help explain it?

[geoffchalcraft]

Colin.... In another word.... YES! Brilliant! That's very helpful.... and means I'll stick with the plan and just upgrade where I can - CS5 and/or Lightroom. (I have mainly used PS Elements until last year when I installed Lightroom 3 - but it ran so slowly on my machine that it's almost impossible to use properly.)

Thanks to all for your advice!

[Colin Southern]

Colin.... In another word.... YES! Brilliant! That's very helpful.... and means I'll stick with the plan and just upgrade where I can - CS5 and/or Lightroom. (I have mainly used PS Elements until last year when I installed Lightroom 3 - but it ran so slowly on my machine that it's almost impossible to use properly.)

Thanks to all for your advice!

Hi Geoff,

Glad I could help.

For what it's worth, Lightroom and Photoshop are really targeted at different groups; Lightroom's greatest strengh is that it's cheap, and able to deal to large number of images at once -- but the "downside" is that although it's easy to make global changes to images (and apply these to batches of photos), once you get past global adjustments and into localised adjustments - although it does some (in a comparitively limited way) - it's a bit like lining up an 18 month toddler against an olympic sprinter in a race when compared to Photoshop.

Photoshop on the other hand excells at ALL kinds of adjustments in comparison, but is often (unjustly) criticised for not having the capability to handle lots of images (just think "wedding photography" and you'll get the idea), but folks seem to nearly always forget that Photoshop also ships with Adobe Bridge - and that (in conjunction with Adobe Camera RAW) allows you to manipulate and batch-process large numbers of images with ease. I routinely open up to 250 images at once for things like bulk white balancing - exposure correction (even things like batching GND filters). You can apply changes to all files automatically (as you would white balancing), or synchronise a given image with as many (or as few) images as you want. Once one has invested in a little training in learning how to do these things, it's incredibly powerful.

[geoffchalcraft]

OK, well it's definitely CS5 for me then.... LR may come in handy for batch jobs. I got LR at a 'student' rate so it's not all that precious to me. Thanks.

[Colin Southern]

OK, well it's definitely CS5 for me then.... LR may come in handy for batch jobs. I got LR at a 'student' rate so it's not all that precious to me. Thanks.

If you're going to work it hard though, a PC with a healthy amount of RAM helps - I use Windows 7 x64 with 12GB RAM for my main PP PC these days.

[geoffchalcraft]

Hi Colin.... that sounds like a decent machine to me. (but what do I know? I've had my current one for nearly six years, WinXP, 4Gb RAM, only 80Gb HD!). At the age of nearly 60 I wonder if my next computer will outlast me? I have a daughter nagging me to get a Mac but I still think I'd get more 'bang for my buck' with a PC, which I'm going to need to step up to Windows 8 (next year?)

Geoff

[Colin Southern]

Hi Colin.... that sounds like a decent machine to me. (but what do I know? I've had my current one for nearly six years, WinXP, 4Gb RAM, only 80Gb HD!). At the age of nearly 60 I wonder if my next computer will outlast me? I have a daughter nagging me to get a Mac but I still think I'd get more 'bang for my buck' with a PC, which I'm going to need to step up to Windows 8 (next year?)

Geoff

Hi Geoff,

Many (Mac owners) will have you believe that a Mac is more than just a computer ... and more than a religious experience too. The way I see it (as an owner of many Apple devices), is it's just a tool (as is the PC), and with the exception of having an Option key instead of an alt key, and a command key instead of a control key, Photoshop runs EXACTLY THE SAME on either platform.

Probably the thing that makes the biggest difference in either system though is using a solid state hard drive if you're working with hundreds of images at once, and don't like waiting.

[Viana]

Your computer will not outlast you, Geoff unless you want to not have the latest and greatest software, which "old" hardware will typically not run. I change machines on average of every 3-4 years.

The biggest difference between Macs and PCs is the Operating System. As an owner of at least half a dozen Macs, one who works on PCs and has owned them, I find the Mac OS far superior.

Lightroom is a much more useful program for most people, especially photographers. Photoshop has a very high learning curve. I have both and lots of other programs as well, and am very skilled at most of them, but use LR the majority of the time. Photoshop is not only for photographers but all sorts of graphic artists. These days, most photographers use LR for photo organization and general PS adjustments. They use Photoshop for special processing.

[Viana]

Forgot to mention, that if you use Photoshop, many of the filters will not work on 16 bit.

[geoffchalcraft]

Colin.... the point about the solid-state HD is taken, thanks - I hadn't even thought about that.

Viana..... Thanks for your reply, though I'm trying to steer clear of the Mac v PC debate. I think I'll stick with what I know (and can best afford). I'm happy with using Photoshop thanks to many years of using PS Elements - yes, I know it's very much the little brother of full PS but the 'methodology' is very similar - anyway, it doesn't scare me! The second point, about Photoshop not working in 16-bit with many filters - that's what I thought but Simon Garrett (the first person to reply on this thread) suggests that CS5 can handle 16-bit with most filters (3rd party plug-ins excepted). So, I'm happy to go for a PC, with the hardware suggested by Colin, using CS5 and finally getting my existing LR3 to work at an acceptable speed. I'm even going to suspend my 'requirement' for a quality printer and let a friendly commercial lab do the work. I've been using a wonderful Epson Pro 4000 for a few years but now I'm moving from Canada to the UK it has to go - for the princely sum of $50! (anything rather than putting it on a dump!)

Cheers again everybody,

Geoff

ps..... 'Viana"...... got me thinking. It's like a cross between two names.

[Colin Southern]

The second point, about Photoshop not working in 16-bit with many filters - that's what I thought but Simon Garrett (the first person to reply on this thread) suggests that CS5 can handle 16-bit with most filters (3rd party plug-ins excepted).

It's probably somewhat of a moot point because I doubt that any alternative program is going to have those filters anyway. And regardless, it's a mouse click to convert the image back to 8 bit if needed.