Alley in Pisa, Italy

by Lars Kotthoff

submit your photo


Hall of Fame
View past winners from this year

Please participate in Meta
and help us grow.

Take the 2-minute tour ×
Photography Stack Exchange is a question and answer site for professional, enthusiast and amateur photographers. It's 100% free, no registration required.

I've noticed that in a lot of my night shots of cityscapes, red lights (e.g. neon signs on buildings, etc.) tend to come out as big red blobs:

Not very good example of big blobby red lights

The above was taken with my Canon 500D.

What can I do to reduce this? (Either as I'm taking the photo, or as a post-processing step.)

share|improve this question
    
It seems like this area of the photo is out of focus, in which case the only fix is to bring it into focus. Does this also happen in focused areas? –  Evan Krall Oct 3 '10 at 8:00
    
Related: Why do bright red flowers end up without details? –  mattdm Jun 12 '11 at 17:22

3 Answers 3

up vote 14 down vote accepted

What you're seeing in that shot is overexposure. Unlike overexposure in a day time shot,where the blown highlights tend to go pure white, the red light from the sign caused overexposure in the just the red channel. Thus all the different tones of red have become 100% red and detail is lost.

It can be fixed by reshooting at a faster speed / smaller aperture pulling up the shadows, or blending multiple exposures (using HDR techniques).

Did you shoot raw? If so you may be able to fix it without reshooting, by taking advantage of the extra headroom in raw to reduce the exposure. If you have Adobe Camera Raw there is a tool called "recovery" which attempts to fix this kind of blown highlights though it doesn't always work that well.

share|improve this answer

Camera Shake and Overexposure

As well as overexposure, I believe there is some camera shake (look at the lighted windows to the left), which will tend to turn anything into a blob.

Camera Shake

I'm guessing that in order to try and get enough light in for this mostly-dark scene, your camera slowed the shutter right down.
When the shutter is slowed down, any tiny movement of the camera can blur the image, as we see here.

fix

Using a faster shutter speed, or steadying the camera with a tripod or similar would help.

Overexposure

The lights are being overexposed (almost certainly) because the camera is exposing for the scene as a whole. Most of the scene is very dark, so the camera thinks it needs to let in lots of light. This means that for the light areas, it lets in too much light, with the result that the neon sign gets blown out (especially the red channel - as @Matt Grum points out).

fix

The fix for this is to dial the exposure down - probably using your "exposure compensation" control. Knowing when to do this will come quickly with experience. Fortunately, with digital you can always check on the back of the camera and reshoot if necessary. :)

Using your camera's spot metering mode would probably help, too, but it brings its own compromises. Check your manual for more details on this.

share|improve this answer
    
Camera Shake was my first thought looking at the sample. –  BillN Oct 8 '10 at 19:02

Some cameras allow you to see the histogram for each color channel side by side. That way you can tell if a single color was overexposed instead of the entire image.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.