How to fix blown highlights (blue rings)

[MrPete]

(WHEW! That five-day wait before being allowed to post is a killer... used up most of my Christmas vacation waitinggggggg... :-D )

I am ramping up to do higher-quality 8mm film capture to digital.***

My current challenge: no matter what settings I use, the off-scale white highlights on the film are completely "blown" and surrounded by pretty large blue fringe. (See below for a middling case -- bad but not the worst I've had...)

Does anyone have ideas or scripts or plugins that can handle this kind of thing? This seems worse than the usual Chromatic Aberration, although I'm open to all suggestions.

Thanks much! This looks like a GREAT community. I look forward to contributing here over time...

Blessings,
Pete



*** I have a MovieStuff Sniper HDL, which came with an early HD Camcorder, the Canon HV20 -- very poor low-light sensor... I'm converting to use my wife's Nikon DSLR, direct to HDMI, and from there to my PC... I'll explain more about my setup once I am more confident that my process is actually working! :-D

[Reel.Deel]

Attachments can sometimes take some time to get approved. If you don't want to wait any longer then upload your picture to a 3rd party image host. Even better is a small unprocessed sample from the original source.

[MrPete]

Originally Posted by Reel.Deel

Attachments can sometimes take some time to get approved...Even better is a small unprocessed sample from the original source.

So I see!

OK. Fixed the attachement.

And there are two clips at http://www.ds.org/files/avisynth

blown-bluefringe1.avi is 40MB, a few frames from one section...
blown-bluefringe.avi is a couple hundred frames, around 200MB (once it is done uploading in a few minutes from now)

Please ignore other defects... this is almost-raw (about half the frames are removed already, and it is vertically flipped so it makes more sense )

[MrPete]

Hmmm... staring at these clips, I think it IS chromatic ab... the blue shifts depending on where it is on-screen.

That doesn't help me. It only shows up for blown highlights... and I don't know how to correct for it in AviSynth in any case

[johnmeyer]

I do film transfers using Roger's Workprinter. I think the Sniper also uses the external aerial lens. Alignment is tricky, and if done incorrectly, you will definitely get rainbow fringing. I bought one of Roger's very first Workprinters, and corresponded directly with him. I have copied below the alignment instructions he sent to me over a decade ago.

Before copying that, let me say a word about exposure. When doing film transfers, you have to understand that film has a much, much greater exposure lattitude than does video. This means it can record a much greater luma range, from very bright to very dark, without going all the way to black, and without bleaching out the highlights. Unless you have a very, very expensive camera that lets you create a custom gamma curve inside the camera, you cannot possibly capture this entire range. What's worse is the fact that the exposure meter on your camera will expose for the average luma value, and this will often completely blow out the highlights on white shirts, etc.

So, here's what you do. First, if your camera has a "spotlight" function, enable it. This is designed to reduce the exposure for a subject on a stage, lit by a follow spot. When used during film transfer, it will also reduce the exposure if it senses a really bright object.

Second, if you can, use a camera that has zebras. Set this to 100+ or 100. Nothing lower. Then, if you see zebra patterns, which show that something is being overexposed, use the EV adjustment on your camera to reduce the exposure until the zebras disappear. Remember to increase this again when the scene changes to a darker exposure.

If you can't stand by the camera and monitor the entire capture, then at least watch a few minutes just to make sure you aren't getting any zebras.

If you follow these directions, you should end up with a slightly under-exposed result. That's OK because you can almost always still recover all the stuff in the shadows. To do this, I create a custom histogram in Sony Vegas using its Color Curve function. There are functions in AVISynth that can also be used, including HDRAgc (I think that's what it's called). The key is that you want to increase the exposure of the darker pixels without changing either the very darkest or very lightest pixels at all.

I'll put Roger's quote in the next reply.

[johnmeyer]

From Roger Evans, many years ago:

Therefore, here is the best procedure for setting up the focus on the WorkPrinter:

This is based on the assumption that you camera has the required 12x or better optical zoom. A 10x zoom may cause problems with cropping and final alignment.

With no film in the projector, close the gate and turn on the lamp. Place the focuse lever of the projector in the vertical position to start. Put the camera on a column head tripod (to allow incremental vertical movement). Start with the camera on wide angle and place it ridiculously close to the condenser lens, like about one foot. The out put of the camera MUST be feeding into a full size monitor. Trying to use the built in LCD monitor is a waste of time. In the center of the monitor, one will see a white circle of light. Start physically moving the camera away from the condenser lens very slowly and observe the monitor. The round white dot of light will grow until the gate is visible within. As soon as you feel the circle has reached the edges of the condenser lens, stop and mark the floor with some tape where the center of the tripod is. Now continue moving the camera away from the condenser lens until the circle of light begins to close up again. Stop there and mark that spot on the floor.

You now have a "range" of where the camera can be and still see the entire gate. Place the camera in the middle of this range, which may be an entire foot for some cameras and as little as a few inches for other cameras.

Zoom the camera up to the gate but stop just short of zooming in at this point. You may notice some chromatic aberrations on the edges. Slight re-alignment of the camera up and down as well as side to side will negate these blue or amber aberrations. Moving the camera back a small amount may ALSO be necessary even IF it takes you outside the "range" that you previously marked on the floor. The reason is that zoom lenses will rearrange the elements in the lens when you zoom in, changing the dynamics of the relationship between film plane and CCD. Also, single chip cameras are much easier to align than 3 chip cameras due to the lack of prism in single CCD units.

Load some film in the projector that has a good, crisp image corner to corner. Something bright with good contrast is best. An old black and white cartoon works wonderfully! Adjust the framer knob so that the image is in the middle of the gate. At this point, attempt the initial focus with the CAMERA and NOT the projector. After focusing, note the frame lines of the film. They should be straight across with no bowing or bending (pin cushion and barrel distortion).

Now, this is the most important part: If they are not straight, then adjust the PROJECTOR focus lever (not the camera!) until the lines are straight across, EVEN IF THE IMAGE GOES OUT OF FOCUS. Remember, as noted before, the projector focus lever not only changes the focus, it can change the shape of the image. Also, remember that the camera lens is part of the equation as well. Therefore, if the image goes out of focus as a result of straightening the frame lines, focus can be easily recovered by adjusting the camera focus.

The biggest mistake most people make is adjusting the focus of projector only, when the focus can be manipulated by both the camera and projector. Once the frame lines are straighten and the camera focus is reattenuated, the image should be sharp corner to corner with no soft spots and no chromatic aberrations. If it seems close but not quite correct, move the camera back a bit. The further away (to a point) the better the image will be as longer lenses have a natural flat field characteristic that helps straighten things out.

Try this method of setting up your unit and I think you'll have better results. As I offer to all my clients wherever they are in the world, I am happy to call you and talk you through the set up one step at a time.

Roger

[MrPete]

Thanks, John! That gives me a few things to work on. Not sure if I can eliminate the CA "mechanically" or not... we'll see.

A few FYI's:

* The Sniper has some obvious differences. Your Workprinter focus/alignment instructions involve both projector and camera focus. My Sniper has no projector lens or focus. I am shooting directly on the film plane.

* It will be interesting to see what options I have for modifying my capture process. My wife has some high end pro DSLR equipment that I am occasionally borrowing for this project... normally it seems hardly likely that people would have any of this for film conversion... just WAY too expensive!

- Nikon D800e DSLR with 36mpxl FX sensor (closed down to DX to get the 1.5x multiplier). No noise at all to ISO 1000+, better results than the Sniper's Canon HV20 even at ISO 10,000+

- 70-200mm f2.8 zoom lens with 1.7x TC

- Plus I'm using the close-up adapter that came with the Sniper, and 77-43mm step-down ring.

The only real downside to my rig is that the D800 only allows me to set the shutter speed in full manual exposure mode.... what I would love is a true shutter-priority auto-exposure, and that is apparently not available

I will do some realignment experiments tonight.

In the meantime: I'm still curious if there's a way to remove the blue fringe via a processing step...

[johnmeyer]

Hmmm ... If you don't have the external aerial lens, then I don't know how you are getting the chromatic aberrations. Perhaps something internally is out of alignment. You might want to contact MovieStuff.

There are quite a few threads about removing colored halos. Here is some code which shifts ALL colors down or left. I think it could be adapted to only handle blue. Start by setting Hshift to +2 (it moves the colors to the left) and see what you get. Keep increasing it. Eventually you'll get halos out the other side of the object.

Vshift=0 
Hshift=0 
MergeChroma(crop(fields,Hshift,Vshift,0,0).addborders(0,0,Hshift,Vshift))

This code is for attempting to fix the chroma shift you get with 2nd generation VHS tapes. It may not be exactly what you need, but I think it is on the right track.

[MrPete]

(BTW, how long before doom9 stops asking me stupid "random questions"? Or does everyone always have to answer?)

It does appear that the bloom is radial in a sense: it is not always on the same side of the highlight; depends on where in the frame.

I've been able to greatly reduce the number of frames with blooming; it all seems to depend on the amount of contrast in the frame, and I can't completely eliminate it without switching from auto exposure to manual exposure (which would just be too painful).

I think I will run with what I've got, then move on.

(BTW, MovieStuff no longer services, supports, or responds to questions about any earlier devices. Kinda painful since I've not owned mine all that long! They just dropped EVERYthing else in favor of their new line of machines. Very sad )