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Green Screen Paint – DIY vs Professional – which is better for your chroma key background

Paul Shillito backgrounds, Chroma key 6 Comments

Well after a bit of a break I’m back with what might seem like a bit of a tedious subject of paint for green screen backgrounds, more over, the difference between DIY paint and professional video paint.

This is something which has been bugging me for a while, why is the “professional” paint more expensive and meant to be better than just normal DIY paint you can get from your local hardware store, after all it still just green paint, isn’t it?

Well yes and no. Yes the greenness or purity of the green is important but its not just the colour which you need to get right for good chroma key work, its also the way the paint reflects light back from the surface to the camera. More importantly the evenness of the reflected light which will make a big difference as to how good a key you can pull with the least amount aggressive adjustment in the keying software..

Just like the evenness of the lighting used is important to help reduce hot spotting, if the paint does not reflect the light in the most diffused and even manor you will have almost the same problem as having poor lighting.

In the video I have two panels one painted with a DIY mix and match paint from Dulux and the other with a professional chroma key paint from Rosco. I show with the aid of technical tools like waveform monitors and some extreme tweaking in Adobe After Effects to show what you cant easily see with the naked eye or even tools like the Green Screener app which is one of my favorites for getting the lighting of green screens right.

Although my studio setup is very simple and not very challenging to get a good green screen background, if you have something like a 3 or 4 surface setup like two or three walls and a floor, all painted green like the image from Qcumber Studios below then you’ll need all the help you can get to achieve a well balanced chroma key. The last thing you need is for the paint its self to become a problem because its not reflecting it back in a uniform manner and creates hotspots due to the way does or does not diffuse the light from its surface.

nellastudio

As a bit more back ground info about the panels and paint, i painted three 8′ x’4′ foamex sheets. The Dulux DIY paint needed 3 coats to get a good solid colour and used just about 2 litres. The Rosco professional paint was a bit thinner and need 4 coats to get the same solid colour and used just under 2 litres.

The lights used were my two x 5′ lighting setup I have used in another video http://video-alchemy.com/green-screen-lighting and they were setup to get the best lighting according to the Green Screener app.

Something which is new is that this was filmed with my Panasonic Gh4 in 4k UHD and recorded in 10 bit ProRes 4:2:2 HQ with an Atomos Shugun, this gives a very clean artifact free video image ideal for chroma key work.

The quality of this pairing is really quite amazing and gave me what looked like an equal quality to the Sony A7s which what i was going to use but the small form factor of the GH4 meant that i had less issues with a shallow depth of field that i would of have with the full frame A7s.

Something which is also apparent is that when you get a really good video source even tools like Ultrakey in Adobe Premier can give you some very good results which are almost indistinguishable from the likes of Keylight in After Effects in the end result on Youtube to almost everyone viewing it. Towards the end of the video I’m using Ultrakey to do the chroma key removal with the two colour green background and if you open it up in full screen in 1080p HD on Youtube you can see how clean the edge is even with this less than ideal duo green background.

Comments 6

  1. jenny knott

    Wonderful video and explaination of how the keying process works. i will be referring customers to your YouTube video and web site for their information. I would love to talk to you about your testing as I have a new product that I would like to talk to you about. Please email me at jenny.knott@rosco.com
    Thank-you,
    jenny

  2. Joe

    I think your video is great and your comparison is clear and concise. However I do believe there are some slight issues with your procedures. Mainly Lighting and Color.

    You chose to match your paint with a different product. For a more fair comparison you should have matched the DIY paint to the Pro Paint. And given that you want pure green you should request custom color mixtures. Mainly you want the lowest base with a 50-50 mixture of blue and yellow. The low base is almost clear. Where medium bases or white have more white pigment. Different brands provide different finishes as well. Try flats in several brands. Use a heavy primer and and paint and primer in one paint.

    Your lighting looks like its coming from a single source in the middle. Are you sure you have even light at both edges? If you have a Light Meter (I cant remember if there is a name for the device) measure the light at each side and in the center. Measure the incoming light, not the reflection.

    Also when you paint, and this applies to all paint options, do all your roller or spray strokes in the same direction. Especially with flat paints the surface is rough and may have different reflective properties based on how it was rolled on.

    1. Post
      Author
      Paul Shillito

      Thanks for your comments, the object of the video was to see how much difference there is between using a paint which most people would “think” that was good for chroma-key and one that was designed for the job. I too started out thinking that I could use just a flat bright green paint, however after I tried it I was disappointed to find that that it was not as flat or equally reflective as I thought and then I looked for the professional paint to get the problem fixed.

      I didn’t have the pro paint to match because I was working the other way around, something which I think many people will do, why look for something that is more difficult to find and potentially more expensive if I can get the same result from DIY paint, basically thinking that the Pro paint is a bit of a con.

      I was surprised to see that the Pro paint is not a pure green as i would have thought but this slight difference doesn’t affect the ability of the Keying software to do it’s job, but does what make a difference is the levels of light reflected from the paint surface at different angles and distances from the light source back the the camera. This has the same effect as uneven lighting, even when its on a flat smooth surface. The lights I used were at the sides and equal distance from the screen surface and its centre point too. The paint was rolled on in a random pattern so there should have been no perceivable “grain” or direction.

      This is where the DIY paint didn’t work as well as I thought it should as it looked like, as you say I was lighting it from the centre with the DIY paint with the light fall off the the edges that could be seen in the scopes and levels adjustment.

      The key, to excuse the pun, is the ability of the paint to reflect the light back at a more consistent manner and the colour purity its self is not quite as important as many think as that stays consistent, it’s the variance in luminance which upsets the keying software.

  3. Chris Newman

    Thanks for the information and based on the tests you did, I need some ROSCO paint… or at least a better cloth screen. I was wondering if you had any suggestions for a professional quality cloth background. I am currently using green material I found at a crafts store. The material is a green felt. It works but I am running into hot and cold spots no matter how I light it. But then again, that material was cheap and cost $1.97 US for roughly 2 meters by 1 meters. I wound-up buying my entire green screen 9 feet wide by 6 feet tall for $6 US.

    1. Post
      Author
      Paul Shillito

      Yes, I’m using the Rosco paint now and the greens are much more even and with the GH4 recording in ProRes 4:2:2 straight the keying even in Ultra Key in Premier is very easy and very clean.

      As for the cloth it depends where you are, in the UK there is a company called Bristol VFX http://www.bristolvfx.com/h/products/vfx-fabrics/228/ which is where i got the sample in the video from but it is expensive and several $100’s for the size of your current screen.

      There are companies in the US doing the same but you need to get a sample and references from others as to how good they are. The best ones are foam backed and don’t crease up but more importantly they work like the paint and have a super flat reflection with no hot spotting. If you have after effects do the same as I did and film your cloth then put some levels and curves on it and you’ll soon see where the defects are.

      1. Mike Perry

        A 9 foot by 6 foot screen with eyelets at 1foot centres all the way round the edge would cost around £160.00 plus shipping, but I have seen very similar fabric available from the Rag Place in Hollywood.

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