Chromatic effects of dynamic irises? - AVS Forum
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post #1 of 5 Old 03-05-2013, 01:30 PM - Thread Starter
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I've got a new PT-AE8000U and am wondering if anyone who is better acquainted with optics can help explain something I'm seeing.

When I first set up the projector, the image looked great but after going through the menus and making various settings changes I noticed a blue fringe or bloom coming off the bottom of white pixels. I'm pretty sure it is not outright misconvergence, because single pixel white horizontal lines still appear white. It's just that if there are white pixels below, there's a minor blue shadow cast upon it. Black pixels do not cast a blue shadow over white pixels below.

After a bit more futzing with settings, I found that turning off the dynamic iris noticeably reduces this blue fringe. At the same time, I also notice that turning off dynamic iris appears to make blues richer, for example in the menus.

My understanding is that the iris opens and closes to increase or decrease the overall amount of light coming out the projector. But does it make any sense for the iris to be affecting the characteristics of just blue? If so, what exactly is happening?

TIA.
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post #2 of 5 Old 03-05-2013, 02:45 PM
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Dynamic irises don't just mess with the raw light output of the lamp, they do all sorts of other things with gamma and possibly greyscale too. What you're seeing may well be a side effect of this gamma adjustment or it could just be making some inherent defect more obvious when using the iris mode. Having owned an AE3000 myself I don't have a high opinion of their idea of 'acceptable' uniformity, convergence or uniformity of focus so I'd take the view that you need to swop it out as you'll never be happy (I wasn't) or better yet change it for something else like the Sony VW50ES or JVC RS46.

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post #3 of 5 Old 03-07-2013, 12:14 AM - Thread Starter
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Quote:
Originally Posted by Kelvin1965S View Post

Dynamic irises don't just mess with the raw light output of the lamp, they do all sorts of other things with gamma and possibly greyscale too. What you're seeing may well be a side effect of this gamma adjustment or it could just be making some inherent defect more obvious when using the iris mode. Having owned an AE3000 myself I don't have a high opinion of their idea of 'acceptable' uniformity, convergence or uniformity of focus so I'd take the view that you need to swop it out as you'll never be happy (I wasn't) or better yet change it for something else like the Sony VW50ES or JVC RS46.

Thanks for the answer Kelvin. You're saying the dynamic iris function actually modifies parameters in the video processing pipeline? It's not limited to physical iris aperture changes? That seems silly to me.

I guess that would explain the difference in blue saturation. But still not sure if that accounts for the difference in blue bloom/fringe. The bloom/fringe actually goes down (better pq) as the blue saturation increases (also better pq).

In any case, pq looks better with dynamic iris turned off. I will leave it that way.
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post #4 of 5 Old 03-07-2013, 06:29 AM
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Dynamic irises do more than simply sample a picture and open and close to various extents based on the data read. If that's all they did, they would make whatever whites that are showing in a dark scene look way too dim. So they boost the whites unfortunately clipping those at the very top. Its all a delicate balancing act and in the sony version it really has been perfected. In poorly implements DIs color shifting has been noted.

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post #5 of 5 Old 03-07-2013, 09:55 AM
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Quote:
Originally Posted by mark haflich View Post

Dynamic irises do more than simply sample a picture and open and close to various extents based on the data read. If that's all they did, they would make whatever whites that are showing in a dark scene look way too dim. So they boost the whites unfortunately clipping those at the very top. Its all a delicate balancing act and in the sony version it really has been perfected. In poorly implements DIs color shifting has been noted.

I haven't seen the new Epsons (5010 and newer) but the older 6xxx and 8xxx generations were pretty bad with color shifts. The DI action was usually pretty smooth and unnoticeable though.
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