rgb vs. greyscale scanning

[Dave Aharonian]

I have about 35 4x5 sheets and 25 6x12 negs that I want to have high resolution drum scans made from. Film is mostly tri-x and fp4 all processed in PMK. I have read that it is best to have them scanned as rgb files. I'm curious about the reasons for this as if I scan them as greyscale files the cost is about 50% less than rgb scans. At $45 per scan I'm happy to save some $$ but not if it really affects the image quality.

Thanks for any info!

[chris jordan]

Dave, if the original film is B&W, then there is no benefit to scanning in RGB. If you scan a B&W negative in RGB, the resulting three color channels will all be identical, so that every pixel will have the same three values (128, 128, 128 for example). So in RGB your files will be three times as big as necessary and the scans will be much more expensive.

If you were scanning from color film, to be converted into B&W, then it is a good idea to scan in RGB because then you have three different color channels that you can selectively mix when converting into greyscale. But when starting with B&W film, scan in greyscale and save your money.

~cj

[julian_4860]

What Chris says is right. But I've had drum scan of BW done where one ch. is sharper than the others, so you can choose which ch. to use. However, I've also had scans done where all 3 chnls were equal, so it depends whether you see see anything on their scanner. These kinds of differences are quite common on film and flatbed scanners

[Paul Butzi]

Remember, a negative developed in PMK is anything but monochrome. If I developed negatives in a staining developer, I would be exploring how the quality of the scan could be improved by exploiting the color of the scan.

In fact, now that it's been mentioned, I'll be evaluating my scanner to see if I can get better scans that way, even WITHOUT using staining developer.

[julian_4860]

another thing to try Paul is using NegPos as a conversion tool (PC only). It allows you access to all the default patameters. In colour I'm getting perfectly instep histos from scanning as a linear scan and then inverting using NegPos - never had it before. For pyro BW you could precisely take out (or not) the stain and match the gammas of all three chnls.

[Paul Butzi]

julian- Thanks, I'll check it out.

[Ted Harris]

It's a tossup. IF it is a good well aligned drum scanner then what Paul says has merit. The down side is that there is a good deal of variance in the color fringing from scanner to scanner, although the drum scanners we have tested all had the requisite almsot dead on aligned square wave. Not true of Imacon's necessarily and I mention this because there are labs out there that will tell you an Imacon is a drum scanner when it is not. The color fringing, if it were severe enough (which is highly unlikely on a well calibrated properly operated drum scanner) could offest the gains from an RGB scan.

[Paul Butzi]

Ted-

What I had in mind more than the advantages of scanning, say, pyro negatives, was the idea that for some relatively inexpensive scanners, the alignment and chromatic abberations might be better for, say, green, and ok for red, and then really bad for blue, or some other combination.

If so, then you might get better results from scanning a normal B&W negative in RGB mode, and throwing away the red and blue channels entirely.

Just one more thing to check out. I just finished the LAST development run of film development calibrations I'm doing. Eight film developer/dilution combinations.

Talk about sheer, brutal drudgery. On the bright side, as soon as the film is dry and I read the densities off the films, and entire them in the mondo spreadsheet, I will have accurate development times for TMX and TMY in D-76, D-76 1+1, Microdol-X, Microdol-X 1+3, XTOL 1+0, 1+1, 1+2, 1+3. Whew.

Good news, I guess, for anyone who can use my times. I'll put them up on the web. Maybe I'll take donations to defray the cost. That works out to a big pile of film through the Jobo.

[Brian Ellis]

I've seen conflicting recommendations on this question. David Brooks wrote a lengthy article about scanning black and white negatives in the September, 2002 issue of Shutterbug magazine. He advocates scanning them as slides. His rationale is that scanners are designed to scan transparencies and have a dynamic range of about 3.3, which corresponds to the approximate dynamic range of slides, whereas b&w negatives have a dynamic range of only a half to a third of that. So he says that when you scan a b&w negative as a negative the information from the negative fills only a small part of the scanner's gamut. I'm not saying this is right or wrong, I really don't know, I'm just summarizing his reasoning. Then I've read other articles other places that say there is no benefit to scanning a black and white negative as a transparency. Most notably, IIRC John Paul Caponigro has an article on his web site in which he says that.

So take your pick. One problem for many of us is that if we're scanning 4x5 film in rgb at a scanner's maximum ppi, we can end up with a file either too big for our computers to handle or so slow that the whole process becomes painful. A 4x5 b&w negative scanned at 4800 ppi (the theoretical maximum of the Epson 4990 scanner) as an rgb image will result in a file of more than 2 gigs in size, which isn't practical for most of us. Of course you could scale down to say 300 dpi at your anticipated maximum print size but then you're involved in another area as to which there is some disagreement, i.e. whether it's best to always scan at the scanner's maximum ppi and then scale down in Photoshop or whether you can scale down in the scanner without affecting the quality of the scan.

[Kirk Gittings]

Depending on your scanner there may be an advantage either way in terms of noise. My 4990 has less noise in grayscale than RGB (Michael Mutansky told me in a conversation at the VC conference that certain channels of RGB have less noise. I haven't had a chance to test it).

I actually scan 16 bit grayscale 8x to lessen noise with Silverfast AI Studio. Then I convert it to RGB so that I can use the capture sharpen feature in PK Sharpener (only works RGB) then I convert it back to grayscale. I have tested every option available (except Michaels above ) and that work flow gives me the best starting file on my equipment. It is time consuming but worth it.