Song Of The South - many projects, much info & discussion thread (Released) — Page 26

Zip Doodah said:

What does 'CA' mean?

Chromatic aberration is color fringing caused by photography. Different light frequencies "bend" through the lens at miniscule different angles (coated-lenses attempt to minimize this effect):

As shown in the diagram, the capture-lens focus is thereby imprecise across the R-G-B color slices that compose the complete picture:

Colors slightly out-of-focus are slightly different sized from the one color in-focus. Because the capture lens always is axis centered, simple resizing (which is also axis centered) keeps picture alignment the same. However, for this Song Of The South frame, the axis was at the bottom left corner (!) indicating the frame had been previously misaligned. Enlarging only the Red separation by a pixel or two (height & width) and shifting from the bottom left corner (instead of center-picture) did a good job correcting the problem:

Some of the issues with Technicolor film are related to how the process worked, both in filming and in printing. 2 of the 3 negs running through a Technicolor Camera were bi-packed, the third color record was recorded with a prism. There were huge baffles all around the camera to keep it quieter since they were quite noisy. All three strips were of course black and white film. The lab would then make a raised neg from these materials, then they were printed in a similar manner as a magazine or book. There was a great issue years ago of a magazine called 'The perfect Image' that had a great article on Technicolor.  The shifts we are seeing in color is just as the actual print is.. and watching color shifts happen from scene to scene is common in a technicolor film print. None of this has much to do with the Telecine process in all likely-hood, through the blacks may be crushed in one shot in telecine, then fine in the next since it's only a one light transfer...

Technicolor went to a single Eastmancolor neg somewhere right around 1950 or 51. The real value of those older Technicolor records is that they preserve the color in separations, so they won't 'lose' color photochemically at all... 

I think what Spaced Ranger is getting at is the aberration in the halos of color, not the Tech process. IIRC, the release of Rope had a lot of problems with halos of misaligned color (from shrunken layers of film) but the problem Spaced Ranger ran into before was CA from the scanner. I don't know whether this print has CA (looks like it, as the shrinking of layers usually isn't that easy of a fix) or whether it is misaligned color, but either way, it is miles better than what's out there now.

+1 - I'd be glad to kick in some cash for a rescan, if that's possible...

I don't think the color issue we're seeing in this particular shot has to do with the telecine at all in this case- just a shot with not quite as aligned color, so very common on Technicolor prints. We're luck in that most of the print has much better alignment of color overall

Very interested in seeing a transfer of an IB tech print if it's eventually shared. The quality of the UK broadcast no matter how enhanced is somehow lacking, no offense to all those wonderful people who preserved it. Thanks for sharing the information, Zip Doodah!

Just in case there isn't a shift from 16mm to 35mm preservation, I wanted to demo the process using Zip Doodah's 35mm clip (the ride on the coach) as a color target. The wider the color spectrum in the target, the better the overall correction ... and one setting might suffice as a final or master setting.

In a paint program's histogram function, the individual R-G-B spectrums are filled out using low and high. Then gamma shifts the bulk of the spectrum lower or higher as needed. Usually that's enough. If the R-G-B's seem too weak or too strong, then midtones can expand or compress (dilute or concentrate) the center area of the spectrums. This usually requires some back and forth adjustments before the combined coloring falls into place:

histogram   lo    gamma    hi    mid
R                19   1.4         162  25
G                  6   2.5         234  20
B                  7   2.0         187  25

I find this process still can leave the saturation and/or contrast weak, but I haven't quite worked out an easy joined-R-G-B movement. Until then, a second process of a joined-RGB graph is added to compensate:

curves    1 I/O       2 I/O       3 I/O         4 I/O
RGB       0 : 0       64 : 24   128 : 128  255 : 255

The end result is a nice improvement that can be use in multiple shots:

Finally, for video processing, I use VirtualDub with the Gradation Curves plug-in. One must manually duplicate the paint program's graph to attain the same correction (this required resizing the paint program's rectangular graph to make it 1-to-1 to the plug-in's square graph):

I did this quick & sloppy, but even at that, it looks almost spot-on:

It still needs tweaking (pulling out the purple scarf and the green leaves is proving difficult as the graphs must remain smooth in the process). If Zip Doodah could post a 35mm grab (full-sized & raw) of a full color spectrum shot and then ww12345 post the same 16mm frame (again, full-sized & raw), that might just work for an overall color correction.

poita said:

CA is common on the Shadow unit, misregistered printing as part of the technicolor process usually presents quite differently, and the one-light transfer is responsible for the crush.

Do you still have the print BTW? i.e. could it be scanned again?

I have never heard that and don't understand how that could be. The Shadow is a line array scanner, like the Spirit- so there would be no ability for misaligned or color creep of any kind really. I would be interested in seeing how CA is common on the shadow, as I can't find anything to suggest that. What is clear is that particular shots vary in alignment on the 1971 print. :) 

poita said:

Those are looking promising. I decided to develop a new LUT for the capture process to try and get as much colour out of the faded print as possible ...

Excellent!

BTW, do you (still?) have any of those download's in their "no special settings" capture -- for my ongoing "practical research" -- on how the capture is affected? Also, can you go into more detail about the "LUT" settings (or point to documentation describing it for this system)?

I was curious on what values were adjusted for the LUT (Look-Up Table). Not knowing how this is implemented, my hope was that it was analog in nature (dimmer/brighter light source with shorter/longer exposure) and not digital in nature (like a paint program's rounding-error-cascading integer math).

                               FLAT CAPTURE

First was to stretch out each R-G-B spectrum from it's fade-compressed range to a full range (0 thru 255). This I expect to be the proper approach for correcting faded film, which loses it's contrast in becoming ever more transparent. Note: the sample should have a full range of color for greatest accuracy of color correction -- which I ignored for this test.

                      R-G-B NORMALIZED
                  RED      12-166  to  0-255
                  GREEN   4-176  to  0-255
                  BLUE     4-170  to  0-255                                                           LUT CAPTURE

Clearly, normalization wasn't the approach use for the LUT capture. The LUT capture didn't have the white cartoon teeth that normalization produced. A quick search revealed that gamma was the adjustment for look-up tables in graphics. So, next, the range was left untouched in favor of gamma adjustment. This came close but it also required midtone adjustment for a better match:

          R-G-B GAMMA & MIDTONE ADJUSTMENT
                  RED       1.5  &  -15
                  GREEN   1.3  &   -4
                  BLUE      1.2  &   -3                                                                      LUT CAPTURE

Of course, I don't know how you determined what settings to use for the LUT to pull as much color out of the faded film as possible. Was it from a known movie reference or by a general standard of adjustment?

Here's something interesting. Clinging to my film fade contrast approach, what if normalization was a missing factor needed with the gamma & midtone adjustments? Combining the two sets of values produced this:

I'll test this idea on the coach scene with real people. If this works well, the master color correction might be performed in the analog capture (if possible to make such adjustments), with only minor touch-ups made digitally thereafter.

Interesting. I'd like to see what you could do with the scenes in motion, too, if you have that ability.

ww12345 said:

Interesting. I'd like to see what you could do with the scenes in motion, too, if you have that ability.

I use VirtualDub to apply my tests to the video (see my workflow, above) with the plug-in Graduation Curves. It was the only one I found to do the job of using the results of the paint program tests, and with interactivity, too. It was supposed to be usable in Avisynth (my first choice) but it wouldn't work -- just as well, as Avisynth wouldn't be interactive with this plug-in anyway.

This way, I can give you a handful of numbers, which you can use/tweak on your end. If you use other software, I'm sure there must be an easy way to also use those results. Let me know if you're having trouble getting it into your work-stream.

poita said:

Remember these are all compressed 8 bit images, the capture happens in log12bit or 16bit linear, so you have a lot more control when colour correcting. ... by getting the colour range closer to the desired output at the capture phase, and eke as much colour in each channel out as possible.

That is so awesome! And, of course, your results are way beyond the poor, faded source. A so-much-better starting point for this project! BTW, I think all our computer stuff is stuck at 8-bit R-G-B. Any suggestions of what you do to make use of all those extra colors?  :)

poita said:

As for extending the range to the full width, one has to be careful doing that on any given scene. ... You want to stretch the range, but not too far, otherwise it all ends up flat and lifeless with no dynamics...

Yes, that was my bad. On a still frame, I push adjustments to the still's max. Ideally, a run of the entire film would be made to get it's min-max value, and then a global-range-extending capture could be made that wouldn't crush/blowout the picture anywhere.

BTW, as long as you don't mind my make-work suggestions, I'd appreciate your continued knowledgeable explanations and any references to in-depth information (especially regarding the hardware, it's capabilities, and settings).

I agree - that color is amazing!

Antcufaalb and I  have been working on cleaning up that Reel 3 scene. I hope to have the clip finished (stabilized, dirt+scratches removed, etc.) by tonight, so maybe we can get the clip color corrected at the same time. I know there is a setting in PFClean which will do color grading, so maybe we could do that. PM sent, Spaced Ranger. 

ww12345 said:

Antcufaalb and I  have been working on cleaning up that Reel 3 scene. I hope to have the clip finished (stabilized, dirt+scratches removed, etc.) by tonight ...

From AntcuFaalb's post, I went looking at PFClean and had a Keanu Reeves "woah" moment.  :)  Then I saw the price and my wallet had a Keanu Reeves "woah" moment.  :O  Great things should come of that (the PFClean, not the woah)!  :D

If Zip Doodah has full access to the 35mm files, perhaps he can run an Avisynth script to sample a single frame inside each shot change. That would produce color correction targets for the entire film. I saw such a script once. I'll see if I can track it down, unless you know or have one.