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Meng
02-22-2011, 02:40 PM
In shots with narrow bands of dark against light or light against dark zig zags appear (I'm sure there is a proper name for this) the bands of dark around the yellow in the stripe down the airplane's side. This is very apparent in shots where these bands of high contrast are a small part of the scene, zooming or cropping tighter makes them less obvious until they disappear.

Can someone tell me what this is called and how it can be avoided, if it can at all.

Here is a shot I took a couple of hours ago to illustrate. The exposure has been dropped a bit and the contrast upped a little to make it more apparent. Full scene and crops.

http://farm6.static.flickr.com/5015/5469118066_29761b0f83_b.jpg (http://www.flickr.com/photos/52992484@N04/5469118066/)


http://farm6.static.flickr.com/5099/5469118278_9337274734_b.jpg (http://www.flickr.com/photos/52992484@N04/5469118278/)

http://farm6.static.flickr.com/5214/5468539071_7af4797c90_b.jpg (http://www.flickr.com/photos/52992484@N04/5468539071/)

Andrew
02-23-2011, 01:18 AM
The "zig-zags" are a result of digitizing lines that are not straight up and down or across. Google PHOTOGRPHY ALIASING for some complete explanations so I don't have to type so much.

Meng
02-23-2011, 03:58 AM
Thank you for responding Andrew I'm much more knowledgeable about aliasing than I was before but I'm no closer to understanding how to prevent it from happening to the extent it did in the shot I posted.

Iguanasan
02-23-2011, 07:52 AM
I'm not sure that you can prevent it so much as reduce it as much as possible. Step one, gather more data. So, make sure you are shooting in the highest possible resolution. Also, if you are shooting in JPEG mode make sure it's set to the least compression (Fine, Super Fine) possible. Often you'll see this setting as a jagged line which gets smoothed out as you move up the "fine" scale of the camera settings.

Whenever you process the image always save it with as much detail as you can muster. I edit the RAW image and then save it in JPEG at 100% to avoid that sort of thing as much as possible.

Meng
02-23-2011, 10:57 AM
Thank you Iguanasan, I do shoot only in Raw format and edit that and always save JPEGS at 100%, as those shots were, and this is what is confusing me. All I've read about aliasing says it becomes more apparant as the photo is cropped and this is exactly the opposite, when I crop or zoom these kind of shots it becomes less apparant. I'll keep searching for information.

Andrew
02-23-2011, 06:28 PM
This copy we're seeing at 72dpi is a version that is showing at 100% a 800 x 533 pixels and there are similar problems throughout the photo. It's been chopped down but so have the others. If it was a common problem I'd expect to see some in the second and third photo in high contrast areas around the plane's window. Does the original look OK? Did you do something to the top photo like crop it before you saved it? Your other photos do have aliasing but up at 200% where I'd expect to see some.

Meng
02-25-2011, 12:02 AM
This copy we're seeing at 72dpi is a version that is showing at 100% a 800 x 533 pixels and there are similar problems throughout the photo. It's been chopped down but so have the others. If it was a common problem I'd expect to see some in the second and third photo in high contrast areas around the plane's window. Does the original look OK? Did you do something to the top photo like crop it before you saved it? Your other photos do have aliasing but up at 200% where I'd expect to see some.

Andrew these are Flickr linked so I have no idea what they did with the final image displayed here but the original Raw image has this in it. It was taken with a Canon 40D and a Canon 24-105 f4L IS, this lens has a reputation for being very contrasty. Maybe the anti-aliasing filter in the camera isn't strong enought to deal with it or it's failing, if that's possible. Anyway I thank you for taking the time to think about this, I'll either figure it out or just accept it as a limtation of this body/ lens combination.