Chroma Background

[lobalobo]

<p>Have decided to play around with an inexpensive, light, easy-to-store portrait setup in my living room. Following advice on the Strobist website I've selected most components. What's left is deciding on background. My current plan is to purchase a stand (not a frame) that hangs a single rectangular background large enough for shots from the waist up for a subject sitting on a stool. (That's what I'll be shooting at first.)</p>

<p>My question is whether it makes sense to purchase a chroma key background for the stand. This would make it trivially easy to take the background out in post-processing and replace it as desired. I wonder, though, whether the final image will look unnaturally flat if I do that, as opposed to using a grey or black background. Of course, if there would be visible shadows on the background, the answer is likely to be yes, but I'm not sure there would be any depth in a dark gray or black background anyway, which is what I'll typically prefer. Thanks in advance.</p>

[Matt Laur]

<p>This all depends on how you light the background (which is usually done with a different light or light<em>s</em> than you're using on your subject). It's only flat looking if you light it that way. And if you intend to chroma out a background, intending to replace it with some other scene or texture ... well, same story. That's only going to look as flat as what you replace it with.<br /><br />But don't confuse greenscreen work with "trivially easy," because that also depends on even, well-controlled light <em>on the background</em>. Some subtraction software/strategies are less fussy, but you need to be sure you're not clipping or blocking up any of that background, and of course you also have to know how to mask carefully if your subject has a similar hue in their clothes, eyes, jewelry, etc. <br /><br />Make sure that you're working with a large enough backdrop that you can get it <em>far enough away from the subject</em> to make things like the subject's shadow irrelevent. How big it has to be, if you're shooting torso portraits, depends on your working distance and thus the focual length of lens you'll be using.</p>

[george_ghio]

<p>My solution for that job was an old slide projection screen that I took the screen out of and replaced it with black velvet. I also modified the stand to allow the screen box to be lowered to within a few of inches from the floor. It's not hard to remove the old screen and staple a new in.</p><div></div>

[lobalobo]

<p>Thanks for both responses. The chroma key backdrop I'm considering comes in garish green and garish blue, one on each side. So unless I'm really unlucky about clothing, jewelry, etc., I should be ok, I hope.</p>

<p>Hadn't thought about clipping or blocking the background, but I take it the point is that chroma removal won't work on a value of 0 or 255. So I'll have to be careful.</p>

<p>Will be using a 50mm lens (100mm in 35mm equivalent). I'll have to experiment with the distance of the screen. Another good suggestion.</p>

<p>Do have one question, though, regarding Matt's suggestion that how flat the image is will only be as flat the background selected to replace the chroma-key background. My understanding is that for a background to appear at a different depth from the subject, there must be some visual cue--different degree of focus, a shadow, different lighting--and my thought was that a pure black background (a look I've seen and like) provides no such cue; this is what led me to the chroma key idea. My post was to ask whether I was right, that there is in fact no sense of depth from a pure black background, in which case the chroma idea would work. I am intrigued, though, by the idea that a superimposed background can have a sense of depth. How would one accomplish that?</p>

<p>All in all, I'm thinking that I should perhaps reconsider chroma key idea, and follow George's suggestion of a screen. Still the chroma-key idea is attractive because I wouldn't need as large a screen, this because if I'm replacing the background I can manually erase any portion of the room not blocked by the screen. </p>

[george_ghio]

<p><em><strong>Make sure that you're working with a large enough backdrop that you can get it far enough away from the subject to make things like the subject's shadow irrelevent. </strong></em><br>

Mat is correct in this advice, but, in the context of shooting portraits in a living room, it can be hard to follow. The black velvet background is a compromise that allows for small spaces. It really is quite hard to get a shadow on black velvet. I chose the projector screen/black velvet combo just for this situation. Highly portable, light weight, small package that fits in a small car. <br>

Given a choice I would have at least a 10X5 metre studio with a croma key wall and full width backdrops.</p>

[craig_shearman1]

<p>Shooting chroma key can be very tricky. Have you ever seen color frings around the weatherman on TV? Or the weather map showing up in his shirt or suit? The chroma key background has to be lit very evenly, usually separately from the subject. Then you have to replace it with something on every single photo once you sit down at the computer. IMHO, if you are starting off with studio lighting you are much better off using backgrounds in the colors that you want, where what you see is what you get. There are all sorts of gray, blue, etc., backdrops available in paper, muslin, canvas, etc. You do have to get far enough away (maybe five feet on up) so that shadows don't fall the backdrop, but you have to do that with chromakey anyway. The secret to wrinkles is to let the backdrop be out of focus, which you do both with being a few feet away and keep the aperture a little wide (maybe 5.6 rather than 11 or 16).</p>

[lobalobo]

<p>Thanks to all. Based on what you've said, I'm giving up on the chroma key. I was hoping to avoid a large backdrop and my thought was I could use chroma software to get rid of the background directly around the subject--where removal would be sensitive--and a large digital eraser for the background around the chroma background. But it's not worth the effort, and I'll try something else. Thanks a lot.</p>