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Old May 1, 2006, 9:49 AM   #1
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Hi, I got a digital camera recently.

A 5.1 megapixel good camera.

Gotten some NICE results.

My question is : when I have taken pictures of a building, and when viewing it afterwards, the vertical at least, edges of the building not every edge, is a little "wavy"?? Any idea why? (Camera was set on "more sharpness")

Other than that, any tips on getting the best possible sharpness on a "scenic" shot? Like hills of green grass, etc...?

Thank you.
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Old May 1, 2006, 10:37 AM   #2
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What you describe sounds like the Gibbs effect, which is an artifact of image processing one often sees on cameras that apply too much sharpening. Basically, what happens is that the sharp edge stops being a step and turns into a dip down, followed by a sharp rise up that overshoots the top of the step, followed by a falling back to the right level. In extreme cases, there are multiple ripples at both top and bottom. The answer is to tone down the sharpening.

If you want to post-process in photoshop, you can apply as much sharpening as you think the image can handle. You'll be doing the same kind of thing the camera is doing, so you're not losing anything but time by doing this in post processing. And you gain the control of not applying any more processing than the image can support.


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Old May 1, 2006, 10:46 AM   #3
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Thanks alot. I have been playing with the controls, its a blast. I'll bring down the sharpness, it has a "normal" a "more sharpness" and a less sharpness...think I'll try the "less sharpness" first...
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Old May 1, 2006, 12:48 PM   #4
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As to tips on sharpness for scenic shots, I refer you to the following web site:

http://www.cs.mtu.edu/~shene/DigiCam...-of-field.html

The discussion on hyperfocal distance should be of interest to you. FWIW


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Old May 1, 2006, 3:31 PM   #5
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Thanks, I am reading it.

Maybe you know something about this...

The problem I have been having with my 5 meg digital point+shoot, is, when I shoot a shot of the house here, and get the roof with its grey shingles in the shot, the shingles end up "wavy" on LCD on the camera. When I view the shot on my tv by inserting the memory stick pro into a DVD player i have (RCA), it has the capability of playing a memorystick in a slide show...the image shows on my 20 inch nonflat TV with the same "wavy" edges on the house shingle straight line..

When i put the memorystick pro into my media card reader and connect it to my computer via USB, and open the picture up with PAINTSHOP PRO, its wavy UNTIL, YES UNTIL, I clik in the "image menu" "SHOW AT FULL SIZE".....THEN, the image is gigantic, of course, but it is sharp and there are no wavy lines anymore...

My reasoning is : because the image is so compressed with all the lines of shingles or longg straight line of a tall vertical building, that it just has to "unleashed" to fullsize view, and the wavy lines go away...????

What do you think?






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Old May 1, 2006, 3:51 PM   #6
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This sounds like an aliasing problem. The patterns that appear on a digitalimage that are not in nature due to undersampling cause patterns known as "moire" patterns. If they go away at full resolution, the problem is that your LCD (and your TV display)massively undersamples the original image. When the sampling rate drops below the Nyquist limit (which is two samples per repeating pattern instance, fwiw), you can end up generating artifacts. The common example used in moving pictures is the illusion that wagon wheels are spinning backwards on old cowboy movies. But still pictures can also suffer from aliasing, and that is the moire effect. BTW, this is not specific to the undersampling of your LCD. If you take a picture that incorporates fine structure and the pattern exceeds thenyquist limitof your camera, you will see moire patterns at full res. Generally, if the pattern is massively smaller than your display resolution, you stop seeing the moire pattern. So things that show a moire at full resolution may not show it on your LCD, and vice versa. There are some lens filters that blur the image enough to obscure moire patterns, but most folks don't bother with them. You could do the same thing manually by slightly defocusing an image that was showing a moire pattern. The problem, though, is that your LCD may not show you that there is a moire pattern problem. And, if you use the anti-aliasing filter, you will create a somewhat blurry image, even when there is no structure in the image that would cause a moire.

BTW, moire patterns have nothing to do with the Gibbs effect I mentioned before. That is an artifact of processing, not of sampling.


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Old May 1, 2006, 6:36 PM   #7
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SixOrMoreShooter, You have it right: it is artifacting. tclune's explaination is better than I can do. You can avoid that effect by shooting at a lower resolution, but don't do that. Shoot at high resolution/low compression and downsize afterwards. IrfanView will do a batch downsizing once you figure out the best resolution for your TV.

Don't overwrite your originals when downsizing: those are your digital negatives. Do not change them in any way.
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Old May 2, 2006, 7:53 AM   #8
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Thanks alot for the replies.

Irfanview looks good too.

How can this "aliasing" or "moire" patterns be stopped?

A better camera? More megapixels? Different brand of camera? This is a 5 meg camera. Was looking at a 7 meg that Sony is coming out with soon. Point and shoot, 10 or 12 x optical zoom...would that make a difference?

Or, is it something that ALL digital cameras do?

Maybe there are just some limitations?

Very good knowledge.
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Old May 2, 2006, 8:45 AM   #9
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I did a quick Google search, and this looks like a nice, straightforward and illustrated discussion of moire patterns: http://www.wfu.edu/~matthews/misc/Di...ias/index.html

As I mentioned above, the way to avoid aliasing in your camera is either to use an anti-aliasing filter or to slightly defocus the image. Since moire patterns do not usually happen -- they requrie regular repeated patterns of detail at intervals that are close to the resolution of the camera -- the cure is almost always worse than the disease.

When you are downsampling an image -- e.g., to post on a forum -- you have a couple of options if the dowsampling creates aliasing in the image. First, the standard analytical way to dispense with aliasing is to apply a gaussian blur that removes frequencies above the nyquist limit in the image. I'm not going to bother telling you how to compute that sort of thing because it's normally a bad idea. The problem, as with defocusing the image when shooting the photo, is that it makes the whole image look worse in order to avoid a local problem (you can't cleanly clip the frequencies at the Nyquist limit or above -- you need to "sneak up on it" by applying a filter thatincreasingly suppresses higher frequencies as you get closer to the Nyquist limit, so everything gets more blurry than you would like).

Alternatively, you can choose a different size to down-res to or crop differently, so the detail you care about is still in the down-res'ed image, but the problematic region is either not present or is sampled at a different rate to avoid the aliasing. For example, if you find that an entire 3Kx2K image dow-res'ed to 800x600 has aliasing, you could see if it still has aliasing if you downres a 2.25Kx 1.5K region you care about, or if switching to 640x480 gets rid of the problem. Often, these kinds of changes will get you where you need to go without applying a blur filter before down-resing. But, if push comes to shove, you can always resort to blurring before down-resing. Just try not to overdo it.

A third possiblity is to leave the Moire in the down-res'ed image. Often, it doesn't look bad, it's just artifactual. If it isn't aesthetically offensive, just leave it be.


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Old May 2, 2006, 11:45 AM   #10
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Fantastic link! Thanks. That's it EXACTLY.

style="BACKGROUND-COLOR: #000000"This morning i went t o a camera store, and made a few 4 x 6 prints.

style="BACKGROUND-COLOR: #000000"ha, they came out with NO wavy lines! Only on the LCD does the waviness show, or in paintshop pro when not "opened up" all the way to show the "real size."

style="BACKGROUND-COLOR: #000000"So, I will live with it. The prints came out nice, I'm quite satisfied.

style="BACKGROUND-COLOR: #000000"Maybe the only other way to not see the wavy lines on a LCD would be to try another camera..was thinking about the new sony 7 meg big optical zoom soon to be out with a 3 inch LCD...someday maybe. Maybe that LCD would not show the waviness at times, I have no idea.
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