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Grid highlites around light sources?


Marcus Ian

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<p>So this is kind of odd, and I was wondering if anybody could expound upon my experience here. Not particularly worried about it, since my XTi is most commonly used by my children (5-10yrs), but I had it out for some shooting at the 4th, and noticed a particular problem. ...I certainly am NOT planning on sending it in to Canon for a new sensor ;-)</p>

<p>In a nutshell, the problem appears to be a highlighted grid overlaying the areas surrounding bright light sources. In this case, it was the sun. (as can be seen in the LR screen grab).<br /> I can say with certainty that my XTi hasn't done this before (I used to frequently do this kind of shot), but it is getting old, so maybe it's a result of that...</p>

<p>I'm wondering if anybody can explain the specific mechanism. Obviously it's residual charge across the pixel lines, but why opposite lines, and why perpendicular lines as well? It seems to diminish with distance from the light source, and does not appear in images without a strong source of light in the frame, but it repeats (in this case, it appeared in images shot earlier w/ the sun, but not in following images w/o the sun, and again w/ this) I'll just post the one for now, but can follow up and post more of specific spots in the images.<br>

</p>

<div>00buYz-541909284.jpg.43e1d5041b23587ae4cd85949acea067.jpg</div>

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<p>No, I'm only seeing actual pixels. but normally this should appear as a smooth field (aside from normal noise). The brighter grid lines are actually pixels that are registering higher charge (which gets interpreted as more light), but the lines are actual pixels, and the pattern is perceptible when viewing on screen in fit or fill (ie. well below 400% or even 100%). I just posted a 400% snap so that it would be clearly perceptible to you guys after I have to down size to post.</p>

 

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<p>Just a wild guess: Perhaps what you're seeing is some imbalance between the color channels. The "grid" could be artifacts from the Bayer array after demosaicing. It's possible the channels are out of balance somehow where you have strong light. Are the grid lines on alternating pixels?</p>
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<p>The grid lines are on alternating lines. I hadn't thought about color channel differentiation since the appearance is just lighter, not in a particular color. hmmmmm, let me play with it a bit, I wonder if I can isolate a particular flooded channel.</p>

<p>It is certainly NOT chromatic aberation. CA is the lenses failure to focus all the 'parts' (colors within the light) into the right spot on the film/sensor plane. It is seen most commonly as fringing around the edges of contrasting areas. While this image certainly does have some (somewhere?), it's certainly not really noticeable, nor is it related to the problem I've described.</p>

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Sorry I hadn't looked closely enough to see that grid problem, just the blown secular highlights around the curling hair.

That grid pattern is a real stumper. Even at 4:1 I haven't seen it before in any of my files.

 

Is it there with all photos.

 

Is it there if you go back to the original settings or does it appear as you go go through the development steps you have

applied.

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  • 2 weeks later...

<p>Sorry for the delay in responding :(,<br>

<br />These are RAWs straight out of the camera, and imported into LR. It is there in all the photos that have the sun in the frame, though in a varying amount. In images (between those taken w/ sun) w/o sun, it is not noticeable, and, when present, seems to vary in intensity with the strength of the sunlight.</p>

<p>It's the first time I've ever seen an artifact similar. I suppose when I get a chance, I'll have to set aside some time, and test it out more specifically.</p>

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