B+W film post processing query

[J-P]

I don't know if 'technique' is the right place to put this - but for all of you that scan your own film and post process digitally, I'd like to pick your brains if you don't mind. Please (mods) feel free to move this thread if necessary.

In a digital image, colour information is incredibly important and each colour or channel has a linear value (8bit = 256 per channel). If you scan something in greyscale only... surely you are missing out on RGB values.

I mention this, because at the moment my process is that I shoot digitally, I tend to shoot viewing B+W in camera. I also ensure that I shoot RAW (therefore preserving all colour data). The B+W image I see in camera only acts as a preview and I junk the generated JPEG.

In post production this is important because I have considerably more data and can manipulate my b+w with more subtlety than a simple 256 levels of grey (greyscale).

How does this work at all in scanning B+W film? Would you be better shooting colour film (for this kind of process)?

I'm considering buying a film scanner and developing my own negs... but I'm wondering if I'm going to get inferior data from a B+W 35mm negative.

Did I just utter some evil blasphemy? I'm genuinely curious.

 

[xwhatsit]

Well, you have to remember, that if you are talking B&W from whatever source, you only have one channel anyway. With a 24 bit RGB image you only end up with 8 bits anyway. If you adjust contrast/levels etc. with the 24 bit RGB, because it's going to end up as B&W you will be adjust all channels at once -- so you're getting just the same result, there are still only 256 distinct values (you're just adjusting 3 sets of 256 values at once).

My cheap and crappy digital P&S only does 24bit RGB images. However my film scanner can scan in 16bit B&W (or 48bit RGB). My post-processing software can deal with 16bit images (ImageMagick); after shifting to this from GIMP (which could only deal with 8bits per channel) I see a massive improvement.

So, remember, RGB may have more total image data per pixel, but it's just three sets of a 0-255 range of shades, instead of one set of a 0-255 range of shades. If you adjust all RGB values locked together (I can't see a reason not to do that if you're going to be converting to B&W, please correct me if I'm off base here), then it's just the same result as a single 0-255 channel.

 

[Juan Valdenebro]

The thing is that if you shoot B&W film, you do it because with it you can do things you can't do when shooting color film or digital... From the peculiar "look" of B&W, to the ability of filtering with color filters certain colors in the scene to vary their level on the gray scale, to the ways you can control with exposure and development the version of the scene -talking about contrast- that you want to create on a negative... So if you shoot black and white, you should want to scan it to preserve it, not to change it, just as we scan slide film to preserve its character... But as you like processing digitally, you should shoot digitally, because your whole process will be more flexible to reach the control you want...

Cheers,

Juan

 

[Bruin]

Most scanners can output at least 14 bits per channel. As long as you know how to use your scanning software to get the most out of your film, your B&W scans could look (subjectively) even better than digital shots.

I'd recommend a dedicated 35mm film scanner, Vuescan to get linear RAW scans at the highest bits per channel possible, scan at 3200-4000 dpi, and a development regimen that produces low-contrast negatives. Photoshop can take care of the rest.

 

[payasam]

How did you manage the migration from GIMP to ImageMagick, xwhatsit? The prospect of using 16 bits is attractive, but I do not know what it means and what it entails. I am on Debian.

 

[Kristopher]

The channel mixing you are talking about is done at the moment the picture is taken, by using colour contrast filters.

 

[xwhatsit]

How did you manage the migration from GIMP to ImageMagick, xwhatsit? The prospect of using 16 bits is attractive, but I do not know what it means and what it entails. I am on Debian.

Hi, I'm on Ubuntu, but that's just glorified Debian anyway.

Check out this thread: http://rangefinderforum.com/forums/showthread.php?t=90033

ImageMagick is command-line, which doesn't bother me too much (I'm a complete nerd), but the bottom post I made in that thread may interest you, I'm starting to write a graphical front-end to ImageMagick that just does the useful things I need for film scanning (curves/levels, sharpening, maybe some spotting if I can figure out an easy way to do it).

In terms of what it means and what it entails; I find in GIMP after I've done a lot curves adjustment I can end up with some very obvious `steps' in brightness levels in the shadows and highlights. 16 bit solves that (loss of precision in 8 bit leading to rounding/aliasing issues).

GIMP has been promising 16 bit support for years. So quite a few years ago, a group of people got fed up and forked off the GIMP project into a new one, called CinePaint. It was designed for people who work in the motion picture industry, dealing with 35mm shots frame by frame (jeez, spotting is hard enough on 36 shots, let alone 25 a second!). It has 16 bit support. Unfortunately it still has the GIMP interface from 10 years ago and is not much fun to use. Might be worth a look? http://www.cinepaint.org/

 

[payasam]

Thank you, xwhatsit. In my installation of Lenny, IM does have a graphical interface. I don't know yet if it can do conversions of raw files, which is essential for me. I have seen CinePaint, though without knowing its history. In the end I may just stick with GIMP, which has a number of scripts and plug-ins which I use regularly or often.

 

[J-P]

Interesting. Many thanks for the replies so far, I think I'm a little clearer on it now. I do 'cheat' a bit when using digital. I tend to use either Lightroom or Photoshop CS4 (with Camera Raw).

Juan- I won't dump using digital at all. But I also am intrigued by film. I realise I'll have to start using filters more frequently, but that's just like switching from watercolour to oils. Every medium works in a different way (right)?

@Xwhatsit - My normal processing of black and white images (from 16bit RAW) usually involves tweaking heavily in the greyscale mix. So I'm not really tweaking all channels equally.

I would guess that one way of looking at that, is you produce very similar effects as one would achieve using a coloured filter, but I'm retaining the data in the RAW. I shoot at the moment, knowing that I'm going into post afterwards and I don't mind sitting here making adjustments too much. That will probably have to change...

One easy example would be, say if the sky were a bright blue to white gradient. I could go into greyscale mix and adjust the Aqua/Blue channel. This would give me control over tonal richness/darkness of sky (without me having to mask if off in a separate adjustment layer).

I'm just slightly afraid of losing all this flexibility. However, I think the main reason for choosing the b+w film medium (at least for me) is to remove the complexities and pare things down to something more simple, in which case - do I really need to be doing so much tweaking? Probably not. I probably have to try harder to make images 'in camera' be more final.

One more question (while thinking about this). Is there any particular kind of film which is found best for scanning? I've read that tri-X and HP5 (which were both what I was thinking of using) can produce very grainy scans. It's going to take a long while before I can afford a decent negative scanner anyway, I'll most likely be developing the negs myself and then picking shots and having them either lab printed or get an enlarger.

 

[Chriscrawfordphoto]

Shooting color film lets you simulate the effects of shooting BW film through colored filters by manipulating the color channels when you convert the color image to BW in Photoshop. Here's an example:

Color Original

BW conversion heavily manipulated in Photoshop to simulate shooting through a red filter.

This was shot on color neg film. I would not use slide film for this, it makes great color but converts to BW poorly if the image is high in contrast because slide film can't capture the wide dynamic range of negative films, BW or color.

Still, I prefer real BW film, it gives nicer tonality in most situations and is sharper, though color neg film has finer grain for the same speed compared to most BW films.