what bit depth to scan at?

[timbo10ca]

Is there any reason to scan color transparencies at 48 bit over 24 bit? What is the best way to scan B&W film- at 16bit greyscale, or as 24 bit/ 48 bit color, then convert it to greyscale? Or scan in 48 bit RGB and use only the green channel (thought I read that once)?

I am scanning MF frames (6x6), 4x5, and 5x7 sheet film, with max enlargement to 16x20.

Thanks,
Tim

[Michael Mutmansky]

Always scan at 16 bit per channel. That means 48 bit for color and 16 for B&W.

Now, to add to the complexity, you should scan the B&W in color and then use the sharpest channel from the file only. You drop out the other two in PS. Normally that is the Green channel. A simple test will confirm that.


---Michael

[Peter De Smidt]

I agree with Michael. One thing to note, some scanning programs allow you to specify which channel is made into the greyscale. In that case, you only have to scan in color the first time to determine which channel is better. As Michael said, usually it is the green channel, but this does vary, especially if you use a staining developer.

The advantage to the higher bit scanning is that it gives you editing headroom. If you're not going to do much after-scanning editing, then it's possible that 8 bit would be ok, but given the cheapness of hard drives and computer memory, this doesn't make as much sense as it did in the past.

[timbo10ca]

Oh boy- I'm going to need a new computer then!..... These files are so huge, I can't handle them even at 24 bit depth- a 4x5 tranny at 6400dpi is 2 gigs. Even if I downsample to 3200dpi in Photoshop, I still have a 500Mb file, which my computer can barely handle- it takes all afternoon to work on one image! It takes PS about 5-10 minutes to load the 2 Gb file, and almost as much for the 500Mb file. When I start scanning 5x7, my file size will almost double. How much RAM am I going to need for processing these files?!? My processor is an AMD Athlon Duo core 64 X2 3800+ and my vid card is an NVIDIA GeForce 7600 GT.

[Peter De Smidt]

What scanner are you using, and how big do you plan to print?

What operating system are you using? If it's Windows XP, then the most ram that photoshop can access is 2 gb, unless you add a line to the registry to allow access to 3 gb. With XP, I recommend having 4 gigs of ram. You also want a fast scratch disk.

[Darren Kruger]

Oh boy- I'm going to need a new computer then!..... These files are so huge, I can't handle them even at 24 bit depth- a 4x5 tranny at 6400dpi is 2 gigs.

If you are only going to print at a max of 16x20", do you really need to scan the 4x5" or 5x7" at 6400dpi? what resolution do you use to print your files?

-Darren

[venchka]

If you are using a consumer flatbed scanner, the hardware won't give you more than 2400 dpi. Probably less. No need to exceed that figure. The extra dpi are added with smoke and mirrors and mumbo jumbo. Not good for your scans.

[Thad Gerheim]

I like to scan at high resolution so when I buy that really really big printer someday, I'll be ready! But my scanner tells me a Tiff file won't go any bigger than 2gig. Is the photoshop file the next best option?

[Peter De Smidt]

To make a good print at 16x20 with a 4x5, 2000 spi in the original scan is plenty. Actually, 1440 spi would be enough to give you a 16x20 print at 360 dpi, which is pretty good. Scanning at 2000 spi will give you a little headroom. Obviously, with 5x7 you could do a little less. With 6x6, and assuming you're using a consumer flatbed, scanning at 2400 spi would probably make the most sense, as it's doubtful that your scanner can resolve any more, as others have pointed out.

[Peter De Smidt]

For larger than 2 gb files, you can use the large document format.

[Walter Calahan]

I scan all my B&W as color negatives at 48-bit. Then do the conversion to grayscale in Photoshop.

[Thad Gerheim]

For larger than 2 gb files, you can use large document format.

Thanks Peter, I,m using an Eversmart Supreme and have stitched six 4x5 scans together with panorama maker. With the resulting file I printed 20 inches by 12 feet.

[timbo10ca]

What scanner are you using, and how big do you plan to print?

What operating system are you using? If it's Windows XP, then the most ram that photoshop can access is 2 gb, unless you add a line to the registry to allow access to 3 gb. With XP, I recommend having 4 gigs of ram. You also want a fast scratch disk.

I'm using an Epson V750M Pro. I plan to print at a maximum of 16x20/15x21 depending on the film I'm using (4x5 and 5x7). I would like to get close to that with MF film (6x6) as well- probably a max of 15x15.

I'm using XP- I have just ordered some new RAM, to top out at 4 Gb

How do I add a line to the registry for PS to access the 3 Gb?

What is a scratch disk- I see it in preferences, so I made it to be my 320Gb back-up drive, where nothing else is run from. Should I be saving files to this disk as well?

[Peter De Smidt]

A scratch disk is a disk Photoshop uses when it runs out of ram. It's a good idea to designate a disk that's not in use for anything else for this. It's even better to use a stripped raid array. Regarding the registry change, google "windows XP 3 gb switch". That should get you there. It's not hard to do. A 15x15" print from 2.25" square negative is a 6x enlargement. If you're using an Epson printer, having a file at 360 dpi at final size is a good idea. (Canon and HP printers generally work at 300 dpi.) That would require a scan of 2160 spi. As others have said, with everything properly aligned, flat and at the proper height, the V750M resolves around 2400 spi max. Since that's pretty close to what you need for medium format, I'd recommend scanning at that setting. Scanning at a higher res won't give you any more real information.

[timbo10ca]

Darren, Wayne, and Peter-

I am going on the recommendations I've read here and elsewhere by people who are at the top of the scanning learning tree- Scan at max dpi then down-res it to the scanner's "true" dpi (v750- scan at 6400, reduce to 3200). This gives the maximum quality of scan, over simply scanning directly at the "true" dpi- I have no idea why, but they say there's a difference. I only want to have to do this once, after all. I would hate to lose information in the process when I'm going through the trouble of using LF and MF equipment and processing.

I doubt my V750 is of sufficient quality (or my ability to focus, lens quality, etc) to enlarge past 16x20, so that's where I figure I'll max out with these scans. Of course, I would like to have a max resolution file for the off chance I'll ever print larger, but I think at that point getting a drum scan would be the way to go. I plan to eventually get an Epson 3800, so that will dictate my max enlargement for printing (paper max size is 17x22).

[timbo10ca]

A scratch disk is a disk Photoshop uses when it runs out of ram. It's a good idea to designate a disk that's not in use for anything else for this. It's even better to use a stripped raid array. Regarding the registry change, google "windows XP 3 gb switch". That should get you there. It's not hard to do. A 15x15" print from 2.25" square negative is a 6x enlargement. If you're using an Epson printer, having a file at 360 dpi at final size is a good idea. (Canon and HP printers generally work at 300 dpi.) That would require a scan of 2160 spi. As others have said, with everything properly aligned, flat and at the proper height, the V750M resolves around 2400 spi max. Since that's pretty close to what you need for medium format, I'd recommend scanning at that setting. Scanning at a higher res won't give you any more real information.

Thanks Peter- I can breathe a sigh of relief now......

[timbo10ca]

For larger than 2 gb files, you can use the large document format.

What is this and how do I find it/use it? I searched through PS and can't see it (CS2)

Thanks again,
Tim

[Peter De Smidt]

Regarding scanning at maximum resolution and downsizing to the optical resolution rather than scanning at the optical resolution, there's only one way to know for sure. Try it. If there is a difference in your case, you then have to decide if dealing with the monster files is worth the difference. If there's no perceptible difference in the prints, then obviously it's not worth the bigger files and longer scan time.

IMHO, spending time getting the negative absolutely flat and at the proper height, which you can only find through experiment, will provide the biggest quality gain of any of the various tweaks to improve performance.

Regarding Photoshop's large document format, i.e. PSB format, see: http://www.file-extensions.org/psb-file-extension-photoshop-s-large-document-format

[timbo10ca]

Regarding scanning at maximum resolution and downsizing to the optical resolution rather than scanning at the optical resolution, there's only one way to know for sure. Try it. If there is a difference in your case, you then have to decide if dealing with the monster files is worth the difference. If there's no perceptible difference in the prints, then obviously it's not worth the bigger files and longer scan time.

IMHO, spending time getting the negative absolutely flat and at the proper height, which you can only find through experiment, will provide the biggest quality gain of any of the various tweaks to improve performance.

Regarding Photoshop's large document format, i.e. PSB format, see: http://www.file-extensions.org/psb-file-extension-photoshop-s-large-document-format

Great- thanks. So I open the scanned tiff in PS, save as a .psb file, edit it, then save the final product as a .tiff file again for printing?

[D. Bryant]

Great- thanks. So I open the scanned tiff in PS, save as a .psb file, edit it, then save the final product as a .tiff file again for printing?

1) Open the TIFF file.
2) Make your Edits.
3) Save the file as a *.PSB file. This is your Master Working file. Saving as a PSB is only necessary for really huge files where the pixel dimension on one side is greater than 30K (max of 300K). You can save all of your layers, etc. in a TIF file which will allow greater file compression. That is as long as the file size doesn't exceed 4GB. A PSD file is limited to 2GB in size. So if you exceed the pixel limit or the file size limit save as a PSB.

4) When you are ready to print, flatten the file, resize the image at the desired output size, convert to 8 bit (converting to 8 bit in PS prevents the conversion from being done by the print driver which some say is not as good as PS). How to resize to the desired output is also more detailed than I've listed above.

5) Set the appropriate settings in the PS printer interface and then again in the printer driver interface.

Step 5 is deliberately vague here since there are a lot of possible ways one may set everything. Ditto with the driver settings. Basically we want PS to do Color Management and prevent the printer driver from doing CM resulting in nasty stuff like double profiling.

As for setting Windows XP for use with 4GB of memory the /3GB switch is set by editing the boot.ini file. Editing the Registry directly isn't required nor recommended unless you really know what you are doing. Google for instructions. Be careful making this edit. It's simple and straight forward but if you make a mistake you can cause your system not to boot. For safety sake you can actually copy the line in the boot.ini file and paste it below the original. Edit this copied line. This will give you the option to boot the system with or without the /3GB switch. Once you are satisfied that the switch works properly you can re-edit the boot.ini file to provide one boot option.

Here is how my boot.ini file looks with the /3GB option set:

[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /3GB /noexecute=optin /fastdetect

If you have questions PM me or make a post here for specifics. One thing that will also improve system performance is to increase the pagefile size and to place it on another disk besides the boot drive. Be sure to edit the Performance settings in PS Preferences after configuring the /3GB switch.

Good luck,

Don Bryant

[Bruce Watson]

I am going on the recommendations I've read here and elsewhere by people who are at the top of the scanning learning tree- Scan at max dpi then down-res it to the scanner's "true" dpi (v750- scan at 6400, reduce to 3200). This gives the maximum quality of scan, over simply scanning directly at the "true" dpi- I have no idea why, but they say there's a difference. I only want to have to do this once, after all. I would hate to lose information in the process when I'm going through the trouble of using LF and MF equipment and processing.

Why guess like this when you can know?

There aren't any blanket answers. Each scanner/software combination is different. The only way to find out what is optimum for your particular situation is to try different workflows from scan to print, evaluate the prints, then make a decision on what works best for you and your equipment.

The experiments aren't hard, and they aren't that expensive. It's no worse than doing your personal EI and normal development time testing for Zone System use.

The reason I suggest this is I'm fairly confident that the "conventional wisdom" you site is wrong. I've done the tests I advocate myself, and found different results. I think you'll find that scanning at lower scanner resolutions works at least as well as scanning at maximum resolution from your scanner. Why? Because more data doesn't mean more information. And that's the crux of the problem you are trying to solve.

[sanking]

What was suggested was, "scan at max the dpi then down-res it to the scanner's "true" dpi (v750- scan at 6400, reduce to 3200). "

In my experience this may result in a better scan with Epson scanners. Bruce Fraser recommended the technique of scanning at twice the desired resolution and then dowsizing as a method for reducing noise. If you reduce the resolution by 1/2 four pixels are reduced to one and the noise is averaged. The technique may also smooth the image.

However, whether or not this works is both film and scanner dependent so you might run a test to make sure of the advantage, especially if it involves scanning a 4X5 original at 6300 spi, which would result in a rather huge file, even when reduced to 3150 spi. A more realistic approach for 4X5 film IMO would be to scan at 4000 spi and reduce to 2000 spi, which is closer to the true effective resolution of the V750 than 3150 spi.

Sandy






The reason I suggest this is I'm fairly confident that the "conventional wisdom" you site is wrong. I've done the tests I advocate myself, and found different results. I think you'll find that scanning at lower scanner resolutions works at least as well as scanning at maximum resolution from your scanner. Why? Because more data doesn't mean more information. And that's the crux of the problem you are trying to solve.

[Bruce Watson]

What was suggested was, "scan at max the dpi then down-res it to the scanner's "true" dpi (v750- scan at 6400, reduce to 3200). "

In my experience this may result in a better scan with Epson scanners. Bruce Fraser recommended the technique of scanning at twice the desired resolution and then dowsizing as a method for reducing grain. If you reduce the resolution by 1/2 four pixels are reduced to one and the noise is averaged. The technique may also smooth the image.

Noise is averaged, yes. But then everything is averaged. What I found is that it smooths out the grain a bit, but it also seems to smooth over some sharpness and smooth over some texture too. And of course the effect is both image dependent and algorithm dependent. But again in my experience, you'll only see this in higher levels of enlargement. I surely couldn't see it in 4x enlargement from 5x4 Tri-X from an Epson flatbed. But we all see differently, which is why I advise testing for oneself.

Something I haven't thought to try until now (and I no longer have a consumer flatbed for experiments like this, sigh...) is to compare scanning at, say, 4000 spi and downsizing to 2000 spi to scanning at 2000 spi and applying a small amount of Gaussian blur. Hmmm...

[timbo10ca]

Thanks again everybody- I will work my way through this over the next couple weeks.
Tim

[timbo10ca]

1) Open the TIFF file.
2) Make your Edits.
3) Save the file as a *.PSB file. This is your Master Working file. Saving as a PSB is only necessary for really huge files where the pixel dimension on one side is greater than 30K (max of 300K). You can save all of your layers, etc. in a TIF file which will allow greater file compression. That is as long as the file size doesn't exceed 4GB. A PSD file is limited to 2GB in size. So if you exceed the pixel limit or the file size limit save as a PSB.


I'm not sure what the benefit to the psb file is if you're editting the large tiff then saving to psb....

[Peter De Smidt]

The only benefit is if your editing puts the file over 4 gb.

[David Luttmann]

What scanner are you using, and how big do you plan to print?

What operating system are you using? If it's Windows XP, then the most ram that photoshop can access is 2 gb, unless you add a line to the registry to allow access to 3 gb. With XP, I recommend having 4 gigs of ram. You also want a fast scratch disk.

Peter, what line do you add to the registry in XP....and where? My laptop has 3gb of ram and is loaded with Vista. Do I need to make any changes there? I've noticed that it seems to handle large files worse than my 2gb workstation.

[Peter De Smidt]

Dave, sorry but I don't know about Vista. You might Google "Vista 3 gb switch" and see if it pulls up anything.

[David Luttmann]

Dave, sorry but I don't know about Vista. You might Google "Vista 3 gb switch" and see if it pulls up anything.

Thanks. I'll check.