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Anyone done any chroma key work before?

Discussion in 'Help Team' started by Barney, Jul 12, 2011.

  1. Barney

    Barney Well-Known Member

    As per the title, has anyone done any chroma key work before? I've a shoot coming up where I'm going to have to superimpose a full length portrait onto a background. I'll be taking both elements specifically for the image and I was wondering if anyone had any hints, tips or experiences to share in terms of actually shooting?

    I'm going to have to buy the chroma key background. I've found some muslin ones on eBay for about £40 which I presume will be okay. Am I right? I've read to avoid paper as it's too reflective, but also I'm looking for a background that will fold for storage.

    Also, is it worth looking at some of the free Photoshop chroma key plug-ins or am I as well simply doing a 'colour range' selection to separate the subject from the background?
  2. NosamLuap

    NosamLuap Rebmem Roines

    Never done it... but I've gotta ask the obvious question: if you're able to shoot both elements specifically for the task, can't you just shoot it in one go? (or is the 'background' element not somewhere you can position the subject?)

    Be interested in hearing (and seeing!) how you get on...
  3. P_Stoddart

    P_Stoddart Well-Known Member

    Came across this. Any help? :)

  4. Mark

    Mark Well-Known Member

    Hi Barney,

    All of my chromakey work has been done with video or 'movies', but in order of importance, the critical bits (for me) were:

    1. always getting the lighting totally even across the background, at a reasonable level
    2. getting enough physical separation between the background and the subject. Look at the background as a big reflector and you will quickly find that there is a balance between enough light on the background and not getting any reflected light onto the subject.
    3. Software/hardware. The ability to chromakey successfully with complex edges is very similar to the capability to create mattes/masks on fine hair (etc).
    4. In the 'good old days' blue was the preferred ck colour, but green was increasingly used as sensor technology improved, particularly wrt noise. Nowadays, I'd still have both colours on the rollers and, obviously depending on time, subject, lights (how hot the studio is) and a whole load of other factors, I'd reshoot using both bg colours if I could. If one colour has to be chosen in advance, I'd go for a good matt green absorbant bg (as unreflective as you can find). A can or two of Kenair anti-reflect spray may well come in handy, if you find that you're getting hotspots on the bg.
    All of this is based on capturing highres images, for display on big screens. [And during an age when dinosaurs walked the Earth!] :eek:

    Have fun.;)
  5. Barney

    Barney Well-Known Member

    Ha! Well if I could, I would! No, it's a commission with a particular change of perspective effect in mind. I have it in my mind's eye, the tricky part is getting it from there to the camera sensor and then into and back out of Photoshop looking as much the same as possible!

    Once it's done, I'll be writing all about it my new blog. :cool:
  6. Barney

    Barney Well-Known Member

    Thanks, I'd not come across this one but I had seen similar.
  7. Barney

    Barney Well-Known Member

    Thanks Mark! I'm certainly going to have fun (if the subject is willing!)

    I'm going to have the issue of not knowing where I can set my green screen up without hiring a studio. If I go down the route of buying a background and using Speedlights (as was my original plan) I'll have to be aware of just where the light's coming from if I'm outdoors, otherwise I'd be looking to secure a big enough room to use.

    Maybe I'll be better off looking to hire a studio for this shot but the subject could easily be late/change the date at the last minute so I don;t want to be left high and dry with an impending deadline.

    I'm also keen to know whether a colour range selection will give me a good enough effect or if there is a better way with (preferably free) chroma key software.
  8. NosamLuap

    NosamLuap Rebmem Roines

    Again, I'll caveat this with "I've never done it"... but I'd have thought a colour range selection would work?

    Can you mock it up small scale with some green card and a barbie or something??

    I'd imagine the only critical thing would be even lighting - if you're diffusing speedlights sufficiently to cover a large area evenly, you'll be eating power.
  9. Norman

    Norman Well-Known Member

    I don't know which version of PS you use but this tutorial for CS5 might be useful. Some of the 'refine edges' options are available in CS4 too.
  10. spinno

    spinno Well-Known Member

    I tried that and my case comes up next week....
  11. Barney

    Barney Well-Known Member

    Yes, the lighting is key. I'd have to trial run it a few times first.

    I think the difficulty in separating the background from the subject will be around the hair, that's often where you can get a colour cast from the background and where hair lighting can make it look really unnatural when pasted onto another background. Other than that it should be okay.
  12. Barney

    Barney Well-Known Member

    Thanks Norman, I'll have a good look at that later.
  13. NosamLuap

    NosamLuap Rebmem Roines

    Care to suggest some? ;)
  14. NosamLuap

    NosamLuap Rebmem Roines

    I'm glad I replied with quote above, so we can see that I replied to something and I'm not just talking to myself...

    Rather bad form to delete your comment after folk have replied to it, don't you think? (I thought the forum software prevented deletions/edits after replies were made?)
  15. Barney

    Barney Well-Known Member

    Quite, I thought that you were going mad Paul!

    Just to update, I'm now weighing up either buying a green screen and hiring a studio. My main concern is getting the lighting right. With my own screen I can practice, but in a studio the lighting will be more controllable.

    It's going to be a tricky shoot. I'll be shooting from ground level up which means that to get my subject totally surrounded by the green screen it will have to be both quite high & the subject closer to the screen than I'd like. There's a reasonably priced 6m long screen on eBay which I'll think I'll plump for if I can't get a studio for less than £60.

    One thing that's exciting me about this shoot though I that I'm doing a couple of things, one of which although done in video seems not to have been done too much in still photography before while the other seems to be a real novelty. Certainly I'm finding very little reference material online.

    I've got a fall back shot which will work just as well if not better, but that still requires green screening.
  16. Mark

    Mark Well-Known Member

    Stills photography, when done well by normal mortals, has a degree of additional image detail over similarly-budgeted video that shows up any artefacts from Colour Separation Overlay effects. Normal mortals tend not to have access to the sort of hardware that can minimise or even eliminate those artefacts (fringing etc), although recent computer / software combinations are increasingly sophisticated at more affordable prices.

    I'm not sure how complex this project is, Barney, but wish you the best of luck. I think I'd go for the studio option, it'll cut down on any "Pepper's ghost" effects, although if you're good at using 'curves' you can usually optimise the visual balance of the two images.
  17. Barney

    Barney Well-Known Member

    Well I'm running CS5 and my PS skills are rudimentary, hence the desire to get as much right in camera as I can.

    Ha ha, thanks Mark. Maybe it's too complex, but now I've the shot in mind I can't not try it. I wasn't familiar with the concept of "Pepper's ghost" at least by name, and after having a quick search online I'm struggling to see how it might apply to this scenario. Can you elaborate?

    I'm struggling to find an affordable studio with a screen higher than I'd be able to put together myself. My concern with using a studio is that I would have no chance to play around first, so I'm erring on buying a screen just so that I can try it out before hand.

    The complexity of the scene revolves around the perspective I'm trying to achieve. I think having my own screen will allow me to have a trial run first and learn from that. I need to get shooting angles right for the shot to look real before I even start worrying about artefacts etc.

    As I said, I do have a much simpler idea as a safer option, so I'm going to shoot both and if the complex idea is just too much I'll always have the simpler shot to fall back on. I've an idea the ed might prefer the simpler one anyway, but I've set myself the challenge now so I'm not backing out! :cool:
  18. Mark

    Mark Well-Known Member

    One of the most visible artefacts of Pepper's ghost -even when using semi-silvered mirrors - was the very different colorimetry that the reflected image had from the 'background'. Not only were the colours 'wrong' (when comparing the two parts of the image), but even the basic luminance curves had to have significant changes in order to make the two parts 'look right'.

    Before that it takes a fair deal of planning to make sure that any shadows show exactly the same lighting angles, and 'hardness/softness' of light, etc.

    I seem to remember that it all got so complicated that studios ended up building complex sets rather than trying to stitch foreground and background together. But just one look at Cameron's "Avatar" shows what can be achieved, just the question of the $300 million budget now hey mate? :eek:;):D

  19. Barney

    Barney Well-Known Member

    Nope, still can't see the connection! :confused:

    I can't see how using a green screen will have the same effect. What gets reflected, where from and on to what? I've tried searching for the the two terms in connection, but the only references I can find with them both in are on how to achieve a Pepper's ghost with chroma key.

    Getting green light spilling back off the cloth is, to me, a different issue and simply shooting a white balance shot at the start of both shoots will sort that out.

    Hence the 'easier' shot with the sun behind me for the background which will be a simpler lighting set up for the chroma key shot. I try to do the same for the second shot, but it does limit my possibilities.

    Chroma key software has come on in leaps and bounds over the last few years and the days of it looking obvious are long gone. It's now standard practice in TV, never mind films as this clip shows:
  20. Mark

    Mark Well-Known Member

    True Barney, but hire an Arriflex Alexa at £1k a day for the capture, plus an Avid Xpress DV, plus the Boris plugin, and your £60 for a cloth drop is probably just enough to get the lattés. Results today are light years beyond what we were able to achieve with the old blue screens, but it still costs more than my pocket money to get good results.

    Re Pepper's ghosts - I wasn't referring to the technique, just the result. The matching process in post (to produce high quality final images) is very time consuming, especially if the shots are not taken in a studio. Not at all impossible, and I hope you get the shots that you want. In fact, I'm sure that you will!!


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