Friday, September 26, 2008

How to create a photo with a pure black background

I recently posted an image on Flickr with an all black background. One of the first comments (by basswulf) asked if I shot the image with a black background or if I did it in post processing. It was actually some of both; most of it was handled in camera with a black background supplemented by a minor bit of touch up after the fact. I thought I'd share here how I typically do this type of shot.

My buddy, super photographer and all around great guy, Rich Legg, wrote an article about creating a photo with a pure white background. My technique is similar but slightly different because I use Paint Shop Pro instead of Photoshop and I'm doing a black background instead of a white one.

I start by shooting against a black background. In this case, the background simply consists of a black piece of fabric suspended by the overhead floor joists in my unfinished basement. I try to put a bit of space between my lights and the background to eliminate light spill onto the fabric. I also try to orient the lights so they are not pointing at the background. Doing this helps give a nice even black background and minimizes the amount of touch up work required.

1 Black background startHere's the starting image exposed at f/14 with a 1/160th shutter speed and ISO 100. Without flashes, this exposure setting would cause the entire image to be almost completely black, even with the overhead lights on. Exposing this way helps produce a black background and lessens post processing work. As can be seen, the background is very close to black. In spite of all this, if you look closely, you can see a bit of detail on the right side. This is where the fabric ended and some of the items in storage in my basement can be faintly seen. A combination of ambient, a little spill from the strobes and being stopped down caused them to start fairly dark but visible.

2 Black background by faceAbsolute black, in RBG color space, is when all three color components are zero. Zooming in close to the face on the left side, we can see the background has values close to black but not entirely black. In fact, it's a very, very, very dark gray.

3 Black background hand detailLooking at a zoomed in portion of dark detail on the hand, we can see the green and blue components are very similar to the black, but the red is a bit higher. This means its similar to the background but has some additional information providing subtle details for the eye.

4 Black background histogram adjustmentSince the goal is to get the background black, I want to adjust the image so the background's three components are all zero while maintaining the relative value of red component in the hand. The best tool I've found for this is the Histogram Adjustment. This tool allows a number of adjustments, but for the purposes of this image, we just want to adjust the lower bound. By sliding the black pointer on the left side up from 0 to about 10, we cut off all the very small variations on the black side of the image without significantly changing the lighter portions.

5 Black background by faceNow, when we look at the background, we can see it's gone to pure black.

6 Black background hand detailBut we still have some red component in the details, so we haven't completely lost them.

I didn't post an overall image at this point, but the faint portions of unwanted background detail on the right side of the image are greatly reduced. In fact, I couldn't see them at all. But when I ran the color picker over that area of the image, I did see RBG values other than 0, 0, 0, so I knew there was still some more work to be done.

7 Black background negative pre touchupA cool trick is to change the image into a negative. By doing this, the mostly invisible details in the black background suddenly show up as tints when the background is made white. The blue/gray details clearly visible here on the right were nearly impossible to see in the positive version.

9 Black background negative by faceAs can be seen in this close up, the previously all black section is now pure white.

8 Black background negative post touchupThe next step is to select the paintbrush and set its color to pure white. Now I just paint out the details I don't want on the right side.

10 Black background finishedOnce all the background that I want to finish as pure black is painted a pure white, I again select the negative image adjustment and everything changes back to the proper colors. At this point the background is pure black and the image is ready for any further processing I may want to do to it.

Note: Click on any image to see a larger size.

1 comment:

Stephen Shelton said...

Thanks for this. I once did this somewhat by accident, but then forgot how I did it. It's been driving me crazy. You've helped me remember that I played with the histogram. Awesome.