This week we will talk about photographing computer and TV screens, we will only talk about LCD and LED screens because the older CRT screens that are much more difficult to photograph are mostly not used anymore (thankfully).
Today with LCD and LED screens you can actually get pretty good results by just aiming the camera at the screen and snapping away, but there are still a few things that can go wrong:
Glare and reflections
This is probably the most common problem when photographing any reflective surface (including screens, obviously).
Glare happens when light from any source is reflected on the screen and obscures the actual image that is displayed, in the following image there’s a small desk lamp on camera’s right shining into the screen:
Glare is easy to predict, light that hits a surface is reflected at the same angle in the opposite direction, in the diagram below the red lines represents the leftmost and rightmost rays of light that hit the screen, the yellow area is where the light is reflected into, if the camera is in the yellow area you will see glare, on the other hand if the camera is not in the yellow are you will not see glare – that simple.
In the next picture, I moved the camera to the other side of the screen to get out of the glare area and I got a nice glare free image:
Another option is to move or tilt the screen so to change the glare area without moving the camera or to place something between the screen and light source to block the glare.
Bad exposure (image too dark or too bright)
The camera is designed to think everything you photograph is on average middle gray (at least in brightness if not color), this works out really well because most scenes are in fact, on average, close enough to the brightness of middle gray.
But this fails miserable if what you are photographing is mostly white or mostly black – and since most computer programs today use a white background you are vey likely to hit this problem when photographing computer screens.
In the following picture I loaded a picture that is half pure white and half pure black and used spot metering to expose for the white side – the white is gray-ish and everything is dark:
And then I repeated this for the black side (the picture is blurry because I took it hand held and the shutter speed wasn’t fast enough, please ignore the blur):
To fix the problem I’ve used an image manipulation program to draw a middle gray box on the screen and used this for metering (zoomed in so I see only gray in the viewfinder, switched to Av mode, set my preferred aperture, half pressed the shutter to see the shutter speed the camera selected and then switched to M mode and set those values).
With the exposure set I took another picture of the black and white image and this time both the white and black are correctly exposed.
Tip: if you can’t get both correctly exposed reduce the screen brightness.
Note that for accurate results I should have metered using 18% gray but just choosing somewhere in the middle of the L slider (of the HSL color representation) gets me close enough.
Incorrect white balance (strange color cast)
After we got the exposure right it’s time to also get the colors to display correctly.
To demonstrate the problem I’ve used Google image search to look for “red” and found a nice image of a red rose (image from here), just photographing it gets us an image with muted dark colors:
This is because the camera sees all this red and assumes that some of the color is caused by the light being red – so it makes the picture less red to compensate.
To fix this I’ve used the same gray image I’ve used for exposure to set a custom white balance (check your camera manual to learn how to set a custom white balance) and now I’ve got this:
Tip: you can shoot in raw and set the white balance in post processing, just make sure you have at least one shot where part of the screen is pure white or neutral gray.
Balancing screens with ambient light
Screens are pretty bright, especially with the factory default brightness setting (that is designed to be so bright it catches you attention from across the store), room that have screens in them are usually not so brightly lit – this makes taking a picture with both a well exposed picture on the screen and well exposed background difficult.
To demonstrate this I’ve placed a green toy dragon on top of my screen and turned the brightness all the way up (back to the factory setting):
To bring back the dragon I’ve simply used flash, to avoid causing glare I’ve used what we talked about in the beginning of this post, I’ve moved the flash to the side where it almost doesn’t reflect into the camera and used a black card to “hide” the screen from the flash to remove what’s left of the glare):
This is very much a “flash picture” with all the typical flash shadows, but it was easy to take and we see the dragon – I will write about eliminating flash shadow in a future post.
Flicker (vertical or horizontal stripes)
LCD screens have a florescent tube at the back of the screen and florescent lights flicker (they change both brightness and color), you see this with very fast shutter speeds, video cameras and cameras with electronic shutters (where the camera often reads the sensor line by line and not all at once).
To solve this you have to set the shutter speed so the camera picks up an entire flicker cycle (or several cycles).
In the US the electric frequency is 60Hz (so one cycle is 1/60, two are 1/30, etc.) in most of Europe the frequency is 50Hz (1/50 for one cycle, 1/25 for two …).
LED screens don’t have a fluorescent tube and should not have this problem (but I don’t have a LED screen on my desk to test this)
Moiré patterns (rounded lines)
Moiré patterns usually are rounded stripes that appear when there’s a fine pattern on the subject where the details are two big to register as a solid color but to small to show up correctly (in order for a shape to show up it has to be more than 2 pixels in size).
Here I’ve displayed this vertical lines on the screen (the diagonal and rounded lines are moiré patterns).
This is difficult to fix in post processing and the best option is to minimize the patterns while shooting, you can do this by moving closer of farther, zooming in or out and changing your camera angle (or making sure the subject doesn’t have small repeating patterns).
Noise (random dots)
Any decent camera will only have visible noise in dark areas and screens are pretty bright so noise shouldn’t be a big problem, but it can still appear in dark areas of the image and around the screen.
For the next picture I’ve maximized noise by setting the screen brightness very low, the camera to very high ISO with a narrow aperture and fast shutter speed and I’ve took a 100% crop from a dark area.
To minimize noise just get more light into the camera (increase screen brightness, use a wider aperture, a slower shutter speed or if the noise is around the screen add more light).
That’s it, see you next week.