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halos in digital images

R

Ralph Honsbeek

New member
What causes these kinds of halos in Digital Photos


4416584617_c01bdf6bdf_o.jpg


http://www.flickr.com/photos/cybergeek/4416584617/sizes/o/

How can they be avoided ?

Thank you
 
Last edited by a moderator:
Cem_Usakligil

Cem_Usakligil

Well-known member
I think there may be a few reasons. Firstly, the air around us is filled with normally invisible particles/fine dust. When you are in a dark room with sunshine coming in through the blinds, one sees this dust very clearly. So this dust also reacts to the flash light and reflects it causing a higher luminosity in the neighborhood of the flash. Secondly, adding contrast to the image (which is done during the raw conversion or automatically by the camera when shooting jpg files) introduces a slight but eventually visible difference of luminosity in such areas. These are what I think the reasons are but I may be totally of the mark, lol. YMMV.

Cheers,
 
C

charlie chipman

New member
I believe what you are seeing Ralph is combination of jpeg compression and a lower level monitor. I suspect that Bart, Asher, and Cem have higher quality calibrated monitors such as myself and thus have a difficult time seeing what you are describing. However my second monitor is lower quality and uncalibrated. The banding in the the black area is clear as day, as well as the jpeg compression artifacts surrounding the guy. When I look at the picture from an extreme angle on my good monitor the effect becomes more visible. Asher, perhaps if you do the same you will see what Ralph is referring to?

What monitor do you use Ralph?

The picture you have up for display is saved at only 35kb's. If you save it somewhere between 150kb's and 300kb's I would guess that the banding you see will no longer be there.

Low quality monitors only exacerbate the effects of low quality files, which seems to be the case here.
 
M

Mike Bailey

pro member
Charlie probably figured out the problem. Also, reducing the contrast and brightness from whatever the default settings - if that's what being used - can make a big difference, regardless of the quality of the monitor. The Samsung CX226BW from its specifications sounds like a reasonably good monitor. Using good-quality hardware-based color profiling equipment would also help considerably.

Even the software used to view the files makes a difference. Sometimes, though rarely, if I use Photoshop 7 to view an image, this type of banding will appear, while using CS2 or 3 will not, with all else being the same. Undoubtedly the same would be true of other photo-editing software.

Mike

______________
Mike Bailey
http://BlueRockPhotography.com
 
Cem_Usakligil

Cem_Usakligil

Well-known member
Cem_Usakligil said:
I think there may be a few reasons. Firstly, the air around us is filled with normally invisible particles/fine dust. When you are in a dark room with sunshine coming in through the blinds, one sees this dust very clearly. So this dust also reacts to the flash light and reflects it causing a higher luminosity in the neighborhood of the flash. Secondly, adding contrast to the image (which is done during the raw conversion or automatically by the camera when shooting jpg files) introduces a slight but eventually visible difference of luminosity in such areas. These are what I think the reasons are but I may be totally of the mark, lol. YMMV.

Cheers,
Click to expand...
I guess I should have waited for an answer from Ralph about what banding he was talking about before jumping the gun with my "answer" above. Because I did not see what banding it was on my monitor and assumed that he was referring to the circular area around the flash where the luminosity of the background is a bit higher than the rest. I still don't see the banding though! I use a properly calibrated/profiled 30" Dell 3008FWP.


Cheers,
 
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