It occurs to me that calling it Auto White Balance is not really accurate, even though that was the intent. It colour enhancement that happens to get close to a white balanced image in many cases.
It is trying to maximise the number of hues in an image, so when an image naturally has very few hues it is going to produce unpleasant results.
However, in some cases, it produces nice results that probably did not look like the real scene. For example, this image from DPReview’s Nikon D5 review camera WB is probably most accurate but I prefer the hue variance version.
Edit: Also, with a standard whit balance picker you need pick a neutral grey, but with this method you need an area with a range of hues. I’ve found that peoples faces often have enough variation in hues to produce good results. So you ‘white balance’ without any neutral grey.
This is getting a bit off-topic won’t you say, since this thread is about film negatives. I would love to see a new thread on the topic of auto wb, starting with a comparison between @Iain’s and @jdc’s methods. Personally, I believe they have different intents.
Hi’ @troodon
Thank you for your post.
My first reaction: This is a surprisingly good result! Why do you need film negative when you can create such a good result just using the basic RT tools? However, after a closer look at your pp3 it seems to me that it is not so straightforward to get the result using only the basic tools.
First of all you apply a reverse tone curve:
And you also use several other RT tools including RGB curves (R and G channel). Therefore, I think that it requires much less RT expertise to obtain a good result using film negative. @rom9 what do you think?
One issue with the raw file is that the color balance does not seem consistent from left to right, being a bit warmer on the left than the right of the frame. Whenever I’m digitizing film, whether positive or negative, I always shoot a “blank” of just the light source, which in my case is a high-quality 5600K LED light panel. I position the film, then remove it to ensure that the area I’m shooting matches with the film. This “blank” does two things - first it’s a white balance check in RawTherapee, which I use for the film (at least if it’s color transparency film). Second, it provides a reference to ensure that the brightness and color are consistent across the frame. This can be done easily by referencing the histogram on the camera LCD. If it’s a very narrow histogram, it means that the brightness is consistent in all parts of the frame. If it’s wider, it means there’s more variation and you need to make corrections. This variation can be caused by the light source being brighter on one side of the frame, by specs of dirt on the light table, or even by using a wide aperture that has darkening on the edges of the frame. With my Nikkor 60 f2.8 micro lens I need to stop down at least to f5.6 to eliminate this vignetting, and I generally use f8 - f11. This screenshot of a “blank” shows that the exposure and color are consistent through the frame.
Personally I haven’t been able to get good results using Film Negative. Maybe it works better with some negative films than others. Yes, with the normal tools in RT, you need to apply a reverse tone curve, and some of the tools work backwards, but it doesn’t take long to figure it out and when you see a slider does the opposite of what you expect you just move it the other way. I haven’t found it to be a big deal.
I haven’t digitized many color negs, and most of those have processed reasonably well by just reversing the curve, getting a neutral gray from the film border and fine tuning with the white balance sliders. Getting it exactly right needs a bit more fiddling. Once you have a good profile it can be applied to other frames in the same film.
I am glad, however, that the bulk of my digitizing is with color transparencies and B&W negs, as they are easier to work with.
To me it’s not only a problem of expertise (that can be gained quickly by reading one of the many tutorials found online, it’s not strictly RT-specific). It’s mostly a problem of the amount of tweaking needed to process a single negative, let alone an entire roll. Specifically, having to tweak RGB curves was the most frustrating thing to me. After you’ve carefully set them up, if you touch anything that happens before in the chain (like exposure or WB), you end up messing up everything, so you’re limited to use Lab controls.
I guess some people have good “eye”, and can quickly get the settings right, and never touch them again. Personally, i’m terrible at that, i’m always uncertain or unsatisfied with my result, and get into an endless loop of tweaking
Moreover, when i found the Wikipedia article i’ve referenced in the other post, i discovered that inverting the tone curve (or using the invert tool in Gimp) is just not the right math to represent how film works (hence the need for manual tweaking). So i thought: why not start with the right math, and then apply some manual tweaking?
Please, can you share the make/model of the panel? I’m alway curious to try different backlights
This is exaclty what i do as well. My wheapon of choice is a cheap speedlight reflecting on a piece of paper. I had ordered a Kaiser Slimlight Plano, but i returned it because it wasn’t bright enough to shoot at f8, and didn’t beat my speedlight+paper setup in terms of “flatness”.
Please, can you post (or PM) one or more samples that are giving bad results? I’d like to investigate the problem
I use a Porta-Trace 8x11" LED light box. I have another cheaper one from ebay I use for sorting slides etc, but it’s around 7-8800K and probably a low CRI. The Porta-Trace gives good color.
The exposure times are generally around 1/4 to 1/15 second, which is the range where shutter and mirror vibration are at the worst. To counteract this I use live view and a 2 second self-timer delay, which works well.
I used to use a flash for the light source, but now prefer the light box because I can leave the aperture at f8 or f9 and just adjust the time. In addition, it means I don’t need a separate focusing light. I also found that it was difficult to get even lighting across the frame for medium and large format film, although it worked okay with 35mm.
I don’t know about the math of just inverting the curve, but it does seem to work reasonably well.
I’ll dig up a suitable raw file shot from a color neg.
You absolutely need some further editing (tweaking?) after having applied film negative. But the amount of editing needed is much less compared to the situation when you use the basic RT tools only?
I suppose that the film negative tool is the first you would apply working on a negative. Where is film negative placed in the pipeline (I assume it is placed very early) and is it designed to be applied only once without the need for adjustments later on? A later adjustment of the film negative settings will surely cause a need to readjust other tools placed later on in the pipeline.
Okay, I’ve played around with Film Negative some more and need to back pedal and apologize (after all, I’m Canadian, eh!). Film Negative does seem to work very well. In this case I’ve tried to do only minimal adjustments such as picking the light and dark gray spots, adjusting the colour temperature and tint, and some basic adjustments to exposure and LAB. Thanks for this great tool!
Yes, that is exactly the goal of the film negative tool: reduce the amount of manual editing needed
It is applied right before Demosaic (step 2 in the pipeline) , and yes, film negative parameters should be set before further editing.
In other words: first use the film negative tool to get a good positive to work with, and then proceed with further editing as you would normally do with a positive image.
@Morgan_Hardwood : great job in the docs page, very clear explanation, thank you very much!
@troodon : thank you for testing and sharing such a great sample!
Can i ask you what type of film it is?
I photographed that negative a couple years ago and at the moment I’m not sure where it is. It’s my dad’s photo from the 1960s, shot on 6x6cm film, probably a Kodak pro film.
