View Full Version : How Much Ram for Digital Processing?

Michael Heald
22-May-2006, 16:05
Hello! With suggestions from folks, I've started getting a handle on what scanner and printer to upgrade to in order to obtain digital prints from 4x5 B&W negatives. Now, I'm trying to decide on the computer upgrade that such processing will require.

Currently, I'm using a P4 with 512 MB of RAM. I anticipate the maximum size that I'll print is 16x20. After recommendations, I read Scanning and Halftones by Blatner, et.al. For a 4x enlargement to 16x20 and 360 dpi printer output, a 4x5 should be scanned at a minimum of 1440 spi, if I understand the reasoning presented in the book and on this forum. My current computer setup handles 8 bit files at this resolution reasonably well.

However, when I jump up to 2400 spi, digital processing is very slow with my computer setup. I imagine it will slow down even further when/if I start processing 16 bit files. I am trying to decide if I need 1 Gig, 1.5 Gig, or 2 Gig of RAM.

So, aside from extra scanning resolution that might be needed to handle cropping of specific negatives, do folks find that there are differences in high quality 16x20 prints if the files comes from 1440 spi, 2400 spi, or even larger scans? Thank you and best regards.


Bruce Watson
22-May-2006, 16:32
I drum scan my 5x4 negatives, both B&W and color. My purpose is often for prints in the range of 10x enlargement. My file sizes end up being around 350MB and 1.0GB. I can write books about Photoshop being slow (I have plenty of time to write between operations ;-)

First things first, you do want 16 bit scans for B&W. Bite the bullet and do it. Well worth it if you do much of any manipulation because you don't have any color to hide behind. What you do will definitely show in the print.

What you want is enough memory available to Photoshop so that it doesn't have to swap to disk. This amount varies from version to version, but a general rule of thumb is about 5 times your scanned file size. Put another way, for best performance you want as much memory as your motherboard can handle.

To carry the performance theme a bit farther, if Photoshop is going to swap to disk (and no matter what you do it will on occasion), you want it to swap to a spindle other than the spindle used by the OS. So you want a second (fast) hard drive mostly used for Photoshop swap space.

More than that, you want to hit the various online Photoshop forums and dig through the archives looking for performance tips that are specific to your version of OS, and your version of PS.

brian reed
22-May-2006, 16:37
Hello Michael,
the best answer is to get as much ram that your motherboard will support. Are you using windows or Mac? PSCS2 will only support 1.7 gigs of ram with windows XP. However Windows XP Pro with service pak 2 will allow you to use a little over 3 gigs, if and only if you edit the boot ini file to turn on the 3 gig parameter. With Mac you can use 3 gigs of ram without doing anything special, so I'm told.

Mark Fisher
22-May-2006, 16:39
My experience with B&W says that 16bit is a must. Anything less won't let do much in the way of tonal adjustments without seeing some posterization. If you want 16x20 images, that makes for a pretty big file and 2GB would probably be the minimum you should go with. I have 1.5GB and only go to about 12x15 and things really start to slow down especially if I create any layers.

Ron Marshall
22-May-2006, 16:47
I have 2 Gig and a second hard drive on a PC and most PS CS2 image manipulations are very fast with 16x20 at 360 dpi output equivalent.

Mike Lewis
22-May-2006, 16:55
I can't tell you about 16x20 print quality from different scan resolutions, but I can give you some computer performance info. I scan color 4x5 negatives and transparencies into 16-bit pixel depth files. These tend to be around 600 MB. I use Photoshop on an Apple Power Mac G4, fully populated with 2 GB of RAM. It isn't enough. Lately I've run the Apple's System Monitor program while editing files and have noticed that the CPUs are never pegged at 100%. However, I do fill up the RAM and the machine swaps files to disk, a lot. Yesterday I mowed my front yard while running a sharpening plug-in on an image file, mowed the side yard while it saved to disk, and mowed the back while the machine processed the image for printing.

I'm beginning to believe that in order to be productive with image files of this size one would need a machine that will address 4GB+ of RAM, and has some kind of RAID 0 storage array striped across three or more disks to use for Photoshop swap and image file storage. CPU type/speed is less relevant, as long as it and Photoshop can handle the RAM you need.

Gregory Gomez
22-May-2006, 17:13
This may not be relevant, but I do tech writing and desktop publishing for a living.

My Macintosh had only one gigabyte of RAM, and it was not enough to handle several programs simultaneously. When I increased it to 1.5 gigabytes, performance improved noticeably.

I would say that if you can afford 1.5 to 2.0 gigabytes, I would go with that RAM size.

I hope this helps.

22-May-2006, 17:13
Memory is cheap these days. Buy all you can fit, you can't get too much of it. Also, get a second hard disk and reserve it for Photoshop. A physical drive, not just a partition. That should speed things up when Photoshop starts writing to disk, especially on a PC.

Photoshop CS2 can effectively use 4GB of RAM. That's for images, the application itself needs some RAM to run, plus the memory for the OS, plus whatever else is running in the background. This means that even 8 GB of RAM would not be too much...

Daniel Geiger
22-May-2006, 18:15
For PS I use a Mac G5 with 3.5 GB RAM and it works ok. What I did notice is that 16 bit processing (particularly spotting with healing brush) is very slow, slower than on a file with twice as many pixels in 8 bit. It seems that it is not only file size, but the 16 bit cost some extra computational power. But as everybody else has said, go for 16 bit anyway.

On the PC, I have 3 GB with the 3GB boot-option (not for photoshop, but for 3D reconstruction software). On the fairly new Dell X dimension box, after I installed the additional RAM, the XP system profiler only recognized 2 GB. After some conversations in French with the computer, reseating RAM banks, restarting a few times etc., I checked available RAM in the 3D application (amira) and there it recognized the 3GB. It seems that XP-Pro can only count up to 2GB.

On the Mac, the buffer RAM in the HD seems to make a difference. I just fried the original 160 GB drive, and installed a 400 GB with 16 MB buffer RAM. All disk operations are noticeable faster.

22-May-2006, 19:24
What I did notice is that 16 bit processing (particularly spotting with healing brush) is very slow, slower than on a file with twice as many pixels in 8 bit. It seems that it is not only file size, but the 16 bit cost some extra computational power.

Daniel, that's 8-bit vs. 16-bit per channel. There are three channels (unless you're working in 16-bit grayscale). Each channel handles 256 levels in 8-bit and 65,536 levels in 16-bit.

In other words, the difference is not linear but exponential. A 16-bit channel contains not twice but 256 times the number of bits than the 8-bit one. And there's three of them, if you're in RGB and not grayscale. That's where the difference you're feeling is coming from.

Jack Flesher
23-May-2006, 09:26
First, RAM:

As said above, XP Pro with SP2 can recognise 3G for any application if you add the "/3G" toggle to the end of the boot.ini string.

I am running 4G of ram in my machine and have about 2.8G available for CS2 (Less than 3 since I have a bunch of other I/O devices reserving their ram space on boot.) However, since everything else has reserved its needed ram, you can assign 100% of the available to CS2 without problems.


Second, SCRATCH:

Also as mentioned above, having your CS2 scratch space set to a different physical drive -- not just a separate partition on the same drive -- from your OS drive will greatly increase performance. This is because the OS pages (same as scratch) to its drive for memory management and will take priority over any other program. Hence CS2 has to sit idle and wait its turn to scratch if the OS is paging. By having CS2 scratch on a separate drive, the two programs do not have to share I/O resources for the same drive and CS2 can move along at warp speed.

Ted Harris
23-May-2006, 09:52
An addendum to Jack's post above on the scratch drive. In addition to being a different physical drive,not a partition, it will also give you best performance if it is an empty drive .... that is don't put another thing on it, save it for Photoshop.

Regarding RAM, its like never being too rich or too thin .... you can never have too much RAM. The Mac world gives you a bit more flexibility at the moment with the ability to add up to 16 GB of RAM on the latest dual core Intel processor machines and the ability to add up to 8 GB of RAM on most of the G5 towers. Given that CS2 can address 3.5 GB of RAM, total RAM of 5 GB should give you an adequate buffer to fully exploit CS2 PS capabilities and do other a few other things in the background. When you can buy RAM for less than $100 per GB that is fully certified with lifetime replacement there is no reason to stint. BTW there are lots of memory suppliers out there I have found www.datamem.com to be among the best of the lot. I have been buying memory, hard drives, etc. from them for 17 years and have found them to be utterly reliable. I had a RAM chip fail as I was installing it on a Powerbook once and they had a replacement out to me FedEx the next morning. Same thing on a CF card that failed. My only affiliation with them is spending money over many years.

Brian Ellis
23-May-2006, 15:13
Ted - How much difference does it make if the scratch disc has other things on it instead of functioning solely as a scratch disc? I have a 120 gig external hard drive that I use as a back up storage device to for photographs and also as a PS scratch disc. I'd guess the photos take up maybe 10 gigs of space right now. I'm wondering whether it would be wise to add a second external hard drive just to serve as a scratch disc?

BTW, I've had a good bit of trouble with external hard drives on my PC. The first one failed after a few months of use (maybe the fault of the movers who just unplugged it without going through the safe removal step), now my computer periodically fails to recognize my second one. I leave it sitting there connected but unrecognized and usually after a week or so it will suddenly, for no apparent reason, once again be recognized for a while. I've gone through that twice in the three or so months I've had it. In doing some research trying to fix the problem I came across a lot of information from people having the same or similar problems so I gather it's not unusual to have problems with external hard drives.

Jack Flesher
23-May-2006, 16:19
Scratch disks II:

First off, having an external drive as scratch is a really BAD idea unless it is a direct SATA or SCSI connection as the I/O speeds are severely compromised by USB, firewire or network. Scratching is a heavy I/O process and because of that you want your scratch disk cabled directly to the MB.

I/O performance in order of preference are currently SCSI drives (U160 and above), then SATA and then IDE. As a practical matter, SATA drives are nearly as fast as SCSI, it's just that SCSI manages I/O better. I am trying to say I would NOT add a SCSI card to a machine that had a free SATA port just for scratching purposes and would probably not add a SATA or SCSI card for scratch if all I had was a free IDE port -- IDE is plenty efficient for scratch purposes. To put this difference in perspective, I replaced a 250G 7200 RPM SATA drive with a 144G 15,000 RPM U320 SCSI drive as my scratch disk and measured the performance gain on an intensive CS2 process (very large file with multiple layers on a large re-size operation with sharpening and noise reduction). The process took 62 seconds with the SATA drive as scratch and 58 seconds with the SCSI drive as scratch -- a 5% performance gain for a SCSI drive that cost 3 times what the SATA drive cost and only had just over half the space. I expect the SATA to IDE comparison would yield a similar, marginal gain...

Sharing. If all you have on your scratch disk is data, I don't see a big problem with sharing it for scratch purposes (assuming it is an on-board drive). If you have programs loaded on your scratch disk, then the OS may tag that drive periodically looking for files and again, the OS takes precidence over scratch and CS2 has to wait its turn. But even here, from a practical standpoint this would be a minimal slow-down.

I think the important thing to understand here is the price/performance equation. An 80G drive can be had for about $40 now (IDE or SATA) -- or about the same cost as 512 MB of RAM. And 80G makes a very adequate scratch drive and offers a huge CS2 performance gain relative to that 512MB ram. So for $40 you can really boost the performance of your CS2 imaging machine.

23-May-2006, 16:45
Scratch disks III:

Underscore everything that Jack said and then definitely make your internal scratch disk Photoshop exclusive. Especially on a PC. Aside from acceess time and order, there is another reason, at least equally important, and that's fragmentation.

While Unix and its derivatives have been created as account-oriented OSes, Windows is still essentially DOS, a file-oriented OS. Account-oriented OSes have always had physical data distribution solved on a system level, while file-operating systems never really got there. Hence fragmentation remains an issue and will have visible impact on speed.

Dedicating an entire disk to Photoshop solves that problem because swap files are temporary and Photoshop cleans everything after itself, leaving the disk effectively empty, with nothing to be fragmented.

Ted Harris
23-May-2006, 17:35
Scratch Disk IV:

What Jack and Marko said and add that IF you don't have room for an additional internal drive buy an external SCSI drive and install a SCSI card if you don't have one. Remember that not all SCSI cards are equal. I recommend the Adaptec 29160N; ASC version for PC's and APD for Mac's.

26-May-2006, 19:01
Adobe has a very extensive page devoted to getting the most out of Photoshop titled "Optimize performance of Photoshop (CS2 on Windows)". Even though it's intended for Windows most of the advice is platform independent. You'll find all of the advice given here plus much, much more.