Photography under florescent

Florescent lights are everywhere – they come in all shapes and sizes, they are inexpensive and they are energy efficient – they are also one of the worst light sources for photography (the bulbs used in street lamps and some industrial warehouses are much worse – but you rarely find those while photographing while florescent bulbs are everywhere).

There are two problems with florescent lights – flicker and color.

Flicker is the worst of the two, florescent lights flicker, they constantly cycle between different intensities and color, each cycle takes 1/50 or 1/60 of a second, depending on where in the world you are.

When your picture captures just part of a cycle you can get a strange color cast, incorrect exposure and even colored bends in you photo.

To demonstrate I’ve the camera to continues shooting mode and a shutter speed of 1/4000 of a second and pointed it at the round florescent bulb that is right above me, I’ve left the shutter button pressed for about 5 seconds and got a lot of pictures of the same light bulb, I’ve combined them for your viewing pleasure (click image to view larger version):

You can clearly see the color of the light changes between pictures and if you look closely you can also see the amount of light the bulb emits changes drastically between shots.

So what can we do? make sure we capture complete flicker cycles, here the electricity frequency is 50Hz (in the US it’s 60Hz, in most of Europe it’s 50Hz) so I’ve set the shutter speed to 1/50 of a second so I capture one complete cycle and re-run the experiment:

Those 16 identical images are different pictures – it’s just that the total amount and color of light of a complete cycle is completely consistent.

And if a shutter speed of 1/50 or 1/60 does not give you correct exposure you can select a longer shutter speed that covers complete cycles – in the US this will be 1/60 for one cycle, 1/30 for two, 1/15 for four, etc. and in Europe it will be 1/50 for one, 1/25 for two, 1/13 for four and so on.

If you remember in the beginning I’ve said the second problem of fluorescent lights is color – so I took just one more picture of that same light bulb, but this time with I’ve set the white balance to daylight:

If you look at the white ceiling around the light bulb you will see it’s green! you can fix this by setting your white balance to fluorescent – but if you have both fluorescent light and daylight or indecent light in the same picture this will cause a strange color cast that’s hard to fix.

If you mix indecent and daylight you can get the indecent to be white and the daylight to be cold blue or the daylight to be white and the indecent to be worm yellow – both will produce acceptable images but if you throw florescent into the mix you get a green cast – and unless you want people’s skin to look sickly green (or you are photographing zombies) you really don’t want a green color cast.

Also, unlike daylight and indecent light (and light emitted by fire) there are some wavelengths of light that are completely missing from fluorescent lights, this will cause some colors to look completely different under daylight or fluorescent lights – and this can’t be fixed by setting the white balance.

Luckily, the color issue with today’s fluorescent lights is not nearly as bad as it used to be and we can expect (or at least hope) this will continue to get better.

That’s it for today, hope this helps you the next time you take photos in a fluorescent-lit room, see you next week.

Photographing Screens

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.