Sharpening Questions

[Jon Schellenger]

Hi everyone!


I was wondering if I could bring up an interesting post/finishing question- What are most of you all doing about sharpening your images? I know the camera does not have an OLPF filter, so how is everyone making the adjustment in post? Just using the OLPF slider in REDAlert? Is there another sharpening tool in another program that is better and more detailed?

I have had my RED since last April, and I have been using Arri Prime lenses along with some superspeeds. Our images are focused, and they look great.

The discussion I am looking to generate here is what are you all doing in post to get tac sharp images.

I just took a 10 hour photoshop sharpening course. Its amazing about how detailed sharpening a still image can be. What about motion picture footage? I know stills are different versus motion picture footage, but I am just curious to see if you all were doing something special out there.

We have been doing a ton of green screen work so I have kept the OLPF compensator off. We have been keying in shake using keylight. Does anyone have any good recipes for sharpening in shake?

Any interesting stories and workflows on this subject would be very much appreciated!

 

[David Mullen ASC]

I know the camera does not have an OLPF filter

It most definitely does have an Optical Low Pass Filter -- if it didn't, the images would be hyper-sharp and horribly aliased. It's because the OLPF is quite strong in the RED, to reduce aliasing, that some post sharpening may be desired.

 

[mikeburton]

For me it comes down to personal taste. When I look at footage from my camera shot with Ultra Primes for example I usually am quite happy with the sharpness of the image and do not apply any sharpening. If I shoot with my older anamorphic Lomo's I'll usually end up adding some post sharpening at the same time as I do my grade in Color, AE, FCP, Scratch etc. Only a bit is usally necessary as you can destroy a nice image from adding too much sharpening to it. Part of what I like about a RED image is the softer overall look it has compared to other HD cams on the market. So I try my best to preserve it's integrity as much as possible and only give the image a bit of a boost in sharpness when absolutely necessary.

 

[Milan Nikolic]

I wonder do you speak of acutance or sharpness of the Red images?

 

[Dan Hudgins]

Still vs. Moving

Still vs. Moving

Hi everyone!
Any interesting stories and workflows on this subject would be very much appreciated!

If you are going to down res from 4k to 1080p, 720p, or DVD it would probably be best not to sharpen at all since you can get aliasing to show up after the down res unless the resize blurs the 4k image first.

bluring a sharpened image to resize can make the result look worse than having not sharpened the image at all in the first place since sharpening brings up alaising, chroma moire, and noise, and some compression artifacts (mostly in the shadow areas).

My programs have a adaptive sharp soft filter that is adjustable to sharpen edges and soften low detail areas. It is useful to reduce "blue noise" in both film and digital images by softening the blue seperation more than the red and green.

I made a sharpened version to show here (in an older post), but the interface seems to have (resized and?) recompressed the JPG and after that the result looked very bad like video. So there is a hazard to sharpening if the images are going to be compressed for broadcast or blu-ray, the TV and encoders and decoders do not have a flat MTF curve, so even if you get things looking good or near the max sharpness limit on your computer, even a little added sharpening done by the cable company, blu-ray player, or TV set can make your images look "over baked". Its better to keep things a little soft so there is some "head room" for the "things" down the line to resize and sharpen your images without them turning into "the bad video look..."

Also looking at still images you cannot judge how the sharpening will peak the aliasing when the images are viewed uncompressed in a filmout or compressed in one of the compressed formats. To avoid a bad surprise when you see your images moving in the theatre it would be good to do some tests before you settle on a level of sharpness to target in your frames.

If you see the IMAX version of "Day the Earth Stood Still (2008)" you should be some light rings around things in some shots, it looks like it was over sharpened then softened for the IMAX conversion or something...

 

[Jon Schellenger]

First off- thank you guys for replying.

Damn David!!! Did I ever have it backwards! I could have sworn I remember reading about a year and a half ago about the fact that it did not have an OLPF and sharpening would be required. I stand corrected, and what you said makes sense to me. Thank god you corrected me on that because I would have looked like an idiot- If not already! he he... I just had it all mixed up in my head.

Mike and Dan- very good points. These have really helped me re-think some things.

Dan, I sure wouldn't mind hearing more about that program you have that helps deal with the blue channel. Sounds very interesting, and coming from doing a bunch of green screen work, I can say that the 5000K really saved my bacon. We made the mistake of doing 3200 on the first few green screen shoots, and those keys are far harder to work with. Since we adjusted our lighting, we have been pulling fantastic keys.

I think on the still images that we are going to export out, I will make my small sharpening adjustments, however, on the actual footage I am not going to touch it.

David, on your features, have you or your colorist messed with the sharpness much?

Also- somewhat of an unrelated question, however, I am going to shoot it to you guys anyway.

Keying with motion blur!!!! I have made my share of mistakes and I have had one hell of a learning curve here lately regarding the keying. When motion pictures shoot blue/green screen special effects shots, what are they doing to control motion blur? Faster shutter speeds to cut down on the blur, or are they shooting everything normal and dealing with correcting the key and motion blur in post? I am guessing they are shooting faster shutters.

We had several shots where there is a ton of movement and the motion blur was normal as you would expect for my settings: (camera was set at 4k, 2.1, 24fps, 48th shutter).

I just never thought about how motion blur would come out while keying. As many of you know, you end up with a weird halo effect around arms & legs and anything else that is moving at a decent speed.

Is there a recipe anyone has regarding motion blur during a green screen shoot? What does the motion picture industry do? David? (Thanks again guys!)

 

[David Mullen ASC]

If you see the IMAX version of "Day the Earth Stood Still (2008)" you should be some light rings around things in some shots, it looks like it was over sharpened then softened for the IMAX conversion or something...

The IMAX DMR blow-up process involves digitally de-graining the 35mm film image and then sharpening the results. This is what causes that somewhat smoothed-over but sharpened look, almost like some HD photography has.

 

[David Mullen ASC]

I'm not an efx person, but from my studies on the issue of chromakeys past and present, photochemical and digital, an issue has always been trying to key moving objects that become semi-transparent due to motion blur.

The problem with using a short shutter speed and getting less blur and sharper edges is that, while you may get a tighter matte, the object can look too cleanly pasted over the background, with a choppiness to the motion as well.

So some efx artists prefer the motion blur and work on dealing with keying a semi-transparent object or blurred edge. In the old days of optical printing, they would sometimes use hold-out mattes that were less hi-con so that the moving object had a little transparency to it in the final composite. I'm sure there is a digital equivalent to that, but it probably involves really knowing how to make composites and having the right software tools.

I've never shortened the shutter speed for any blue or greenscreen work that I've done, it's always involved normal shutter angles.

--

I've played around with sharpening tools in a D.I. but it really helps to do it while looking at a large screen image, not on a monitor. You really want to make sure that it looks subtle on the big screen and not overdue it. In fact, I usually look at a part of the image zoomed bigger to set the sharpening level, and then look at it in normal size.

Also, a typical film recorder like an Arrilaser also can do some sharpening during the film-out, so you have a couple of places where you can adjust sharpening.

 

[Bruce Allen]

David, speaking for vfx, a new option we like doing is to add motion blur on computer afterwards.

Eg shoot with 90 degree shutter. Do effects. Then computer can add some more motion blur after the effects are done. Depends on the shot of course.

Take a look at this:
http://www.revisionfx.com/view_media.php?m=/video/products/rsmb/gallery/carblur.mov&t=mov&s=320,240

ReelSmart Motion Blur from ReVisionFX

RE: sharpening, sometimes when I watch films that did not go through DI, it sometimes looks like some kind of photochemical unsharp mask process was applied. Is this a by-product of a certain printing process, or am I just hallucinating?

Bruce Allen
www.boacinema.com

 

[Matthew Greene]

For keying motion blur and out of focus images as well as for keying real shadows off the screen my first choice is always Ultimatte, a solid very even screen helps tremendously in not having to dial in clean-up parameters. Primatte and Keylight are also good keyers and are preferable in other situations.

I've done many effects shots with motion blurred and out of focus elements without a problem. I can't elaborate too much, but most of the VFX work I've been involved with in the past few years has required results that wouldn't even stand out to a VFX artist.

With regards to ReelSmart Motion Blur, the only note I have is that it seems to work better with higher frame rate footage than it does with 24fps. I think this is because it's doing some tracking work to create the blur.

Sometimes I've added a tad of sharpening to RED footage that's downconverted, usually with just a plain unsharp mask both at low radius and very high radius settings (which enchances contrast more than edge detail).

I've also had very good results keying RED footage shot with 3200K lamps exposed at 200 ISO. 5600K is definitely a better choice for the RED but not the only way to get great keys.

 

[Jon Schellenger]

Again guys, thank you for this info. You have my wheels turning over here.

Matthew, I agree, I can get some decent keys from 3200. For me, they just seem to take much longer to tweak out. The 5600K at 200 rocks!

I can't share the stuff I am working on just yet, but in 2 weeks, everyone will see the keys we are pulling from the RED.

David, as always, thank you for your reply.. You too Bruce. I will check out that software tonight.

 

[Daniel Browning]

RE: sharpening, sometimes when I watch films that did not go through DI, it sometimes looks like some kind of photochemical unsharp mask process was applied. Is this a by-product of a certain printing process, or am I just hallucinating?

Kodak started using chemical sharpening in the 1980's. It's called "development inhibiting release couplers". It drives VFX people crazy because it ruins green screen and causes other issues (just like electronic sharpening in video).

 

[Matthew Greene]

So, keying motion blur from a bad source:

I took the worst green screen clip I have, horrible screen, underexposed at 500 ISO, unevenly lit, using 3200K lights and with motion blur (on arm).

Took me about :30" to get this key from the RAW original just using Keylight and a bit of filtering (don't have Ultimatte authorized on this computer).

Not the best key but passable, given the bad lighting, wrinkles and all. I'm confident better results could be had from Ultimatte in this situation especially in the blur of the arm. And even better when the greenscreen is shot properly ;op

 

[David Mullen ASC]

There are a number of photo-chemical artifacts that increase the feeling of sharpness and sometimes almost look like edge enhancement. Film grain technology contributes to some of this effect, and optical printing can add something like a drop shadow around each grain as they are rephotographed through a lens onto a new piece of film. There can be other edge artifacts from recombining b&w separations to create a new color image, like a halo around dark areas. Certain developers can enhance edge sharpness of grains.

 

[Matthew Greene]

To illustrate what David is mentioning... what better way to check out the grain than by looking at Super 8? I have been playing around with my RED as a film transfer device (frame by frame automated). The process is quick and dirty (not optimal quality) at the moment but below are some captures that show the grain close up. Note: the negative crop had some edge enhancement, the reversal is unenhanced.

 

[Steve Sherrick]

Ah, Matt you are the guy in this article. Cool.

http://www.retrothing.com/2008/03/our-resident-re.html

 

[Matthew Greene]

hahaha, yes, didn't know that was there.

 

[Steve Sherrick]

So, does that machine work well? I have some people who have asked me about transferring some film and I thought the Red would be great for it.

 

[Matthew Greene]

So, does that machine work well? I have some people who have asked me about transferring some film and I thought the Red would be great for it.

Works very well the way it was meant to be used, with friewire video cameras, getting it to work with RED the right way is quite tricky and requires some mods including:

GPI trigger interface,

Slowing down the device (to 1-2 FPS) so RED can keep up with the GPI bursts,

Redesigning the light source to allow for higher color temp. lamps 5600K-6000K for reversal, 10000K ish for negative. (still on this step),

Carving out the device to allow a lens with extension tubes to capture directly off the gate therefore avoiding the plastic condenser lens which introduces softness, optical and chromatic aberrations (I'm still on this step as well with help from the creator of the Workprinter).

In summary, if you plan to interface it with a RED camera it's not ready for primetime, if you're taking it on as a pet project it's going to take quite a bit of expertise and work. Perhaps once we get it working the right way, Roger, the inventor of the Workprinter www.moviestuff.tv will be willing to sell units modified with the RED ONE in mind. If you're using it with digital video cameras via firewire, I highly recommend it for reversal stocks, negatives take some modifications and work which might or might not be worth it depending on how much time/money you're willing to spend.

 

[Steve Sherrick]

Good info Matthew!

I'll keep an eye out for the mods. Could be interesting.

Thanks!