Difference between chromatic aberration and misaligned panels? - AVS Forum
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post #1 of 9 Old 06-15-2014, 07:46 AM - Thread Starter
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Difference between chromatic aberration and misaligned panels?

Is there an easy way to spot the difference between chromatic aberration and misaligned panels on an LCD/LCoS? Is one or the other more linear in appearance or create less/more solid color fringes?

If anyone happens to have pictures showing a difference, that might be a helpful thing to see as well.

I was looking at some newer Sony's over the weekend and decided to pixel-peep a bit, but I was quite surprised by what I saw and would like to know the odds of being able to correct it if I go that route.
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post #2 of 9 Old 06-15-2014, 09:15 AM
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It can be hard to tell the difference; since they often look very similar.
In both cases, white text (or a white grid test pattern) on a black background is the easiest way to reveal the flaw.

CA is caused primarily by the lens: and generally varies across the image (ie, it's more pronounced in certain areas of the image - often the corners, where the lens is at its weakest - and less so in others). Zooming and changing focus also tends shift it's appearance. It's often evidenced as purple fringing.

Misalignment is caused purely by the panels: for this reason, it usually will not vary across the image - so one corner of the image will be misaligned in the same manner as the center and opposite corner. It's also limited in color to either the panel colors, or a combination of two panel colors (so if red is misaligned, you'll get red fringing throughout the whole image. If it's red as well as blue, it'll be purple-fringed throughout the whole image; etc).

So the consistency of said fringing is probably the most reliable means of telling the difference.
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post #3 of 9 Old 06-15-2014, 09:20 AM
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In terms of correcting: CA usually can't be corrected without changing focal point (ie, changing the projector position and focus/zoom often makes it less visible).

Misalignment can be corrected digitally depending on the projector (Epsons often don't have compensation for this, JVC's and Sony's sometimes do: it depends on the model).

Models offering misalignment correction have a few rows of redundant pixels on each side such that correcting doesn't cause any loss of resolution.
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post #4 of 9 Old 06-15-2014, 11:23 AM
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Spitballing here ...

One would think that panel misalignment would be in the same direction everywhere on the screen, while CA would tend to "swap" direction as you cross the center point of the screen ... yes/no?

Of course, you might have *both* things happening at the same time.
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post #5 of 9 Old 06-15-2014, 11:28 AM
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Quote:
Originally Posted by HDTVChallenged View Post
One would think that panel misalignment would be in the same direction everywhere on the screen, while CA would tend to "swap" direction as you cross the center point of the screen ... yes/no?

Assuming its optical characteristics are the same along the whole 'edge' of the lens; then yes, this would be likely. (Though it's not uncommon for a specific corner to be more affected than the others.)

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post #6 of 9 Old 06-15-2014, 06:04 PM - Thread Starter
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I'll have to take a closer look when I get the chance again, but the Sony's seemed to have a very uniform fringe where the colors (green to one side and red/magenta at the top) stayed in their respective places throughout the screen.

The odd thing then, is the similar fringing from my single-chip DLPs..but I'll need to take a closer look and see if the DLPs are really as consistent as I'm remembering.

Would the clarity of the color be any indication? On my DLPs the fringe is translucent and fades to clear near the end (about one pixel-width of visible fringe), but in the Sony's case the color was stark and without taper. It almost looked like someone out-lined text and menu boxes with a permanent marker.

If it's CA, it would probably be easy enough to try different parts of the lens and see what happens, that's good news. I hope panel-alignment isn't something the 40es lost to the price-gap if misalignment is the bigger issue. Would be nice if certain BB stores started carrying these so I wouldn't have to try and judge from the more expensive Sony's..unless they really are a good enough indication once auto-iris is disabled.

Is there a certain amount of fringing that's considered typical or normal for 3-panel, or a typical amount of CA at the $2000+ price level? Or is it all pretty random or manufacturer based?

Thanks for the information so far.
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post #7 of 9 Old 06-15-2014, 06:35 PM
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Quote:
Originally Posted by Ftoast View Post
I'll have to take a closer look when I get the chance again, but the Sony's seemed to have a very uniform fringe where the colors (green to one side and red/magenta at the top) stayed in their respective places throughout the screen.

The odd thing then, is the similar fringing from my single-chip DLPs..but I'll need to take a closer look and see if the DLPs are really as consistent as I'm remembering.

Would the clarity of the color be any indication? On my DLPs the fringe is translucent and fades to clear near the end (about one pixel-width of visible fringe), but in the Sony's case the color was stark and without taper. It almost looked like someone out-lined text and menu boxes with a permanent marker.

That sounds like classic misalignment.

Likewise, the effect you're describing on your DLP sounds like classic CA.


Quote:
Originally Posted by Ftoast View Post
I hope panel-alignment isn't something the 40es lost to the price-gap if misalignment is the bigger issue.

Doesn't look like you need to worry: Sony's literature on the 40ES (3rd page; here) says:


Quote:
Perfect panel alignment

Electronic panel alignment ensures precise colour and clarity.
Any colour gaps are corrected by shifting the blue and red areas
of each pixel into perfect alignment with green.



...so it appears that electronic alignment is possible on this unit; presumably via either a user-menu or the service menu. One thing I'm not sure of is how many pixels out-of-line may be corrected for. The other thing I'm not certain of is what happens if it's a 'half-pixel' (or any non-whole-number); I'm not sure if that's fully correctable since my understanding is correction is done in 'full' pixels only. In which case correction would be to the nearest full pixel.
Which is probably fine, since a half-pixel's misalignment is probably not noticeable from seated distance to begin with...

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post #8 of 9 Old 06-15-2014, 07:46 PM - Thread Starter
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I've only ever heard of it working for entire pixels like you said it should be perfectly fine by the time it's down to half a pixel. I was mostly worried it wouldn't have it at all, but it was only a couple pixels off so I'd imagine it's within the fixable range.

I imagine the opaque appearance of the fringe was because panels (and their fringes) are in focus whereas CA is rarely if ever in focus..is that what you meant by classic cases?
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post #9 of 9 Old 06-15-2014, 08:13 PM
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Yup. But pictures speak louder than words - here's my W1070; I've set it to max zoom (worst-case) - this is what CA looks like:

Bottom-Right Corner:

(Pardon my camera's automatic image rotation!)

Center:



Top-Left Corner:




Ceiling-mounted, it's most noticeable on the bottom-right corner. The center is almost perfect. And it's just barely noticeable at the top-left corner. It varies from unit-to-unit (my previous W1070 was a little better than this). That said, the photo is actually slightly exaggerated: it isn't noticeable during actual video playback or even when used as a PC desktop display. And it's worse here (with zoom set to max) than it is at closer to the middle of the zoom range.

I guess this is what we've been saying: CA won't be uniform across the entire image like panel misalignment is.
Also, like we mention above, you'll notice the purple fringing 'swaps' locations at opposite corners; with it appearing above the grid at the bottom; but below/to-the-right of it at the top.
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Last edited by kreeturez; 06-15-2014 at 08:47 PM.
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