What causes red/blue fringes along object edges on a white background?
Asked 1/19/2012
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When shooting product photos on a white background with a Canon 400D and external flashes, I sometimes see thin blue and red fringes along the edges where the object meets the background. It is most noticeable on dark objects against the bright background, and seems less visible in brighter exposures. In the example, there is a blue fringe on one side of the object and a red fringe on the other. What causes this effect?
Originally by user8160. Source · Licensed CC BY-SA 4.0
user8160
14y ago
2 Answers
5
This is called Chromatic Aberration (CA). In photography its is also known as Purple Fringing. It occurs because lenses have a different refractive index for different wavelengths of light. The refractive index decreases with increasing wavelength. Its most visible when you shoot a dark object against a bright background.
To overcome this problem totally, you'll need to use a better optics/lens. Some lenses have very good control over CA, others do not. You did not mention what lens you are using on your 400D, but I assume its the 18-55mm kit that comes along. If you're not ready to purchase a new lens, I'd suggest shooting in RAW format, and use the Canon's Digital Photo Professional software which have the ability to fix CA issues mostly if not completely in post processing.
As long as you are not doing professional product photography or making large prints, I wouldn't want to spend thousands of dollar for a better lens as you've mentioned you re-size the image to a smaller size.
Originally by user2476. Source · Licensed CC BY-SA 4.0
user2476
14y ago
0
Generated from our catalog & community — verify before relying on it.
This is most likely chromatic aberration (CA), often seen as color fringing. It happens because a lens does not focus all wavelengths of light at exactly the same point, so high-contrast edges—especially dark subjects against a bright white background—can show red/blue or purple fringes.
It can also be helped along by digital sensor behavior: the red, green, and blue sensor elements are separate and can record edge detail from slightly different angles, which can make the misalignment more visible.
Why you notice it here:
- strong contrast between dark object and bright background
- more visible when zoomed in closely
- some lenses control CA much better than others
How to reduce it:
- use a lens with better chromatic aberration control
- shoot RAW and correct CA in post-processing
- check your editing software for a lens/CA correction tool
So the red and blue edge tint is a normal optical/digital artifact, not a lighting color shift from your flashes.
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