Can someone explain bit modes, in simple terms please

[Andy Sharp]

I am reading Martin Evenings Photoshop CS5 for Photographers, it comes with a pretty useful DVD. I have flipped to the part about HDR as I was out taking some evening shots in Perth. We haven't had the image processing talk yet, well I don't think so following our evening out in Chester, anyway the book talks about LDR 16 or 8 bit images and HDR 32 Bit, but we can't see the information in a 32bit image? I am getting a "BIT" confused. Especially after hearing about 64bit windows 7, what's that all about? Hopefully the 64 bit is to do with the CPU processing and nothing to do with images, or have MACs lost their edge?

[Paul Smith]

The term 64 bit in relation to windows does relate to the cpu. It allows for the processing of more data on each cpu cycle and bears no relation to the use of 8/16/32 bit with regards to images.

A bit is a binary unit, it can have a value of either 0 or 1. It is the building block of pretty much anything electronic. An 8 bit image will have 8 bits per channel to describe the colours. In an RGB image (three channels) each channel has 255 possible values from

0 0 0 0 0 0 0 0 (binary, 0 decimal)

to

1 1 1 1 1 1 1 1 (binary, 255 decimal)

which is what the values in photoshop mean when you hover the colour picker over an image and it says something like (210,80,95). It is describing the values of red, green and blue used to make that pixels colour.

If you move to 16 bit you have 65,535 levels within each channel to choose from, 32 bit gives you an unusably large number in the millions that I don't recall of the top of my head. (24 bits is 16 million odd).

What HDR software does is use the available space offered by 32 bit to load all the different exposures you're feeding it and then allow you to adjust what parts are shown in the end 16 or 8 bit image by changing the parameters of how it's processed.

Of course every part of the chain works at different bit depths just to confuse things. Your camera is probably 12 or 14 bit, Monitor maybe 6 or 8, printer probably 8. You can go round in circles trying to fathom it but as with most things bigger numbers are generally better but beyond a certain point the law of diminishing returns kick in.

this is quite good

http://compreviews.about.com/od/multimedia/a/LCDColor.htm

[Lee Iggulden]

Hello Andy

Thanks Paul for replying to this query, I was just coming on to say I am seeing John Arnold tonight who is running the Adobe Photoshop workshop at Cambrian and I will point him in the direction of this thread.

Andy will be doing a small session on HDR processing but as yet we do not know when or what Academy Evening it will be held at first. It all depends on Andy's work schedule (He works on the rigs and Welshot has to fit in with his timetable)

Im sure Paul's explanation is useful and hope it helps you. I will ask John to pop along and make a comment also.

Thanks for the link Paul :)

[TonyHoward]

Hi Andy, Paul has explained beautifully how the bit numbers described for Windows are all about computation performance. What CS5 provides that previous Photoshop versions didn't is the ability to use 64 bit cpu functionality in Macs. 64 bit functionality for CS4 was only available for Windows. This has a marked impact on performance when using this programme as, in addition to other things, it liberates potentially unused RAM. 32 bit systems can only address a maximum of 4 gb at a time. 64 bit sytems can utilise pretty well any amount of RAM you can install. To illustrate this my computer has 8gb of RAM. However, the maximum I could use in CS4 was 3.072gb. Using CS5 I can potentially utilise 7.562gb. This has a significant effect when handling big multilayered files or large numbers of opened files. To take advantage of this you need a Mac with a 64 bit processor and OS X operating system (Snow Leopard for optimal functionality).

Tony

[markcarline]

Theres 10 types of people who understand binary, those that do and those that dont ;)

(sorry!)

[Lee Iggulden]

LOL, You have all lost me totally but really glad to see the forum being used for stuff like this.

I have pointed John Arnold in this direction. But he is probably on the way to the IT Training Suite right now.

Thanks Tony and Thanks Mark

Lee :)

[Andy Sharp]

Nice joke Mark,
Had to think way back to me school days to work it out lol. Cheers Paul and Tony, I have a Mac with Snow Leopard, (10.6 OSX) on it, this week I have been trying out some HDR imaging but I only have CS4, basically CS5 will let me work a lot faster on HDR. I think I am getting there with my HDR images now, I have done 2 so far and first of all on the one I tried to get out to Facebook, I tried to render a 16 bit image and do a little work in CS4 where I couldn't handle the curves, (apparently CS5 has more options for this than CS4), then I found that 16-bit images can't be saved in Jpeg (don't know why?) so saved it in 8-bit and that is the image I posted last night on FB. Yet more reasons for me to upgrade to CS5 here thanks guys, and thanks Lee, be interesting to see what John has to say.
The good news is that I should be enrolled as a student in a couple of weeks so I can get Academic deals on CS5 upgrade and Lightroom too.

[Photo Imaging]

Keep in mind though that when working with 16-bit images, the file size is much larger than you'd have with an 8-bit image, and if you have an older computer, it could have an impact on how long it takes you to work in Photoshop. Although each new version of Photoshop gets better and better with this, not every filter and adjustment is available in 16-bit mode, but most of the commonly used ones are. You can switch to 8-bit mode by going up to the Image menu at the top of the screen, choosing Mode, and then choosing 8 Bits/Channel. Try to work in 16-bit mode for as long as possible though before switching to 8-bit mode. Also, make sure you switch to 8-bit mode before printing the image, or even better, save your 16-bit version as a Photoshop .PSD file and then save a separate 8-bit version for printing.

[Paul Smith]

There's a good review of the HDR improvments in CS5 on John's site.

Photowalkthrough.com CS5 HDR Review (http://www.photowalkthrough.com/photowalkthrough/2010/4/30/pw123-photoshop-cs5-features-how-good-is-hdr-pro.html)

[Andy Sharp]

Cheers Paul,

Have been watching a few of these lately, fact is I have to upgrade to CS5 for college anyway, but it's good to keep up with what else is going on.

[Photowalkthrough]

The answers already given on this thread are pretty complete and entirely correct - good going. Just to sum up, then:

64-bit computers mean the ability to address more memory (the theoretical limit is HUGE but Windows 7 actually limits the maximum memory in a 64-bit system to 8GB for Windows 7 Starter or Home Basic, 16GB for Windows 7 Home Premium or 192GB for any other version). 64 bit CPUs also handle 64 bit data more efficiently which provides some optimisations and a modest speed boost. For the most part "64-bit" just refers to the generation of chip you're using. The main advantage you'll see is from the ability to address more memory - which is VERY good news for Photoshop. As Tony said, 64-bit Photoshop has only become available on the Mac in the latest version. It's been available on the PC for some time.

As for bit depth in a photograph Martin Evening has it right but perhaps doesn't explain it too clearly. When you're editing photos in Photoshop you should be using 8-bit or 16-bit per channel images. 16-bit will give you a better quality image with larger file sizes. 32-bit images are supported in Photoshop but are really only used for HDR and need to be "tone mapped" before they can be viewed properly. They are used to contain a much wider range of brightness values than a normal 8 or 16 bit image which is why your monitor can't display a 32-bit image properly. Tone mapping tells Photoshop how to squidge the 32-bit data down into 16 or 8 bits so that you can display it and edit it.

Personally I work in 16-bit all the time. You can change your bit depth in Adobe Camera RAW by clicking the blue text at the bottom of the window. If you're using Lightroom then you're already using 16-bit.

Thanks for watching and linking to PhotoWalkthrough too. :)

John

[Andy Sharp]

Thanks John, how regularly are the podcasts that you do with photowalkthrough, my new phone can download and play them directly so I should be subscribing tomorrow.

[Andy Sharp]

At present I have 4MB RAM on a 17" Macbook Pro. marketed as Macs best laptop, Running Snow Leaopard OSX 10.6, how do I tell if I have a 64bit processor? It doesn't appear to tell me this in the Specs anywhere. If I have 64bit I will upgrade my RAM to 8GB when I upgrade to CS5.
:blush:

[Paul Smith]

Pretty much all processors are 64bit these days. If it's an Intel Core 2 Duo or i5 or i7 then it is 64bit. If it's the Core Duo that the macbook pro's launched with in 2006 then it's not.

[Andy Sharp]

Thanks Paul,

I think I saw i7 somewhere but hame struggling to find it again. Cheers.:)

[Andy Sharp]

Hi Paul,
I just had a bit of a wobble then, the i7 processor for Macbook pro was only introduced in January 2010 so I rang MCC the shop I got it from, mine has a core 2 Duo processor in it which is still a 64bit processor. It does however boot to 32 bit due to memory allocation problems, which I understand they have now overcome with newer kit. However the processor maintains its 64bit memory access capabilities, so when I upgrade my memory to 8Mb, I will be able to access it all. phew! :yahoo: