PDA

View Full Version : Shimmering pixels on Stills



Lee U
04-06-2009, 11:49 AM
I seen a thread sometime back how to deal with stills that shimer or appear to glitter while panning a still. I can't find it now. These photos are overlayed on video which I pan. Vertical movement or resizing is where the problems is most noticable and I'm sure it has to do with scan lines.
What's the secret..Thanks

ScorpioProd
04-06-2009, 12:16 PM
Turn on ISS for the stills affected (setting in the control tree for the clip) and see if that fixes it.

Rich Deustachio
04-06-2009, 12:25 PM
You can also add a very small amount of blur to help reduce the shimmer.

Lee U
04-06-2009, 02:01 PM
Eugene, I just tried the ISS and that didn't make it go away. Rich, The blur made it less noticable. The picture is desert with a lot of small rocks. Even if I zoom in on the picture it is noticable. I'm not sure if the size of the picture or aspect ratio has anything to do with it since they are fairly large pics (1668x977)(1536x1152)and all different sizes. Even tried the de-fielding filter. Thanks for the suggestions.

Lee U
04-06-2009, 02:35 PM
OK, I tried several things and revisited Rich's suggest of blur. Applied 1.5 on the Y blur for the duration of the zoom, you can hardly tell the blur was applied and the shimmering has stopped.Thanks very much..Lee

Snu
04-07-2009, 12:45 AM
a little late, but for future reference, here's a thread about this issue, the shimmering effect is aliasing.
http://www.newtek.com/forums/showthread.php?t=87478

ted
04-08-2009, 10:01 PM
We get that with images with a higher resolution than 72 DPI. We had this twice this week from stills supplied by clients. It's pretty common. Making them 72 DPI takes care of it.

We have a batch process in PhotoShop to drag a whole group of stills and make them 72DPI.
Best of luck.

SteelPicR
04-08-2009, 11:34 PM
I think Ted is right. This happen to me several times. It has something to do with the way VT is resizing the still image.

SBowie
04-09-2009, 05:56 AM
There's really nothing magical about 72dpi, but resolution is relevant, and - for a given image, "higher dpi = higher resolution".

Consider that if the original image was 'wallet size' (2"x3") in a landscape format, 250dpi would likely work quite well. It represents a resolution of 750x500 [(3x250) x (2x250)] ... which is reasonably close to SD video resolution, and very unlikely to cause the problem described below. But a '4x5' scanned at 300dpi results in an image that is 1200x1500, and there is some risk in that for images of a certain type. The issues are really 'image resolution in pixels' relative to 'project resolution' and image content.

Single pixel high lines in photos are normally non-existent. For a certain type of content, though, if an image file's resolution is much higher than the project format, it's quite likely that radical down-scaling of fine detail will result in features that are a single pixel high. If that happens, you'll run into inter-field flickering on a static image, and shimmering on vertical movement. You can also run into a moiré issue, which can look like shimmer, but which isn't necessarily resolution related - http://en.wikipedia.org/wiki/Moire

The good thing is that a little blur (or manual scaling) is usually all you need for either issue.

billmi
04-09-2009, 10:06 AM
Nicely explained Steve,
I'm constantly having this discussion with magazine art editors who don't get it and insist that supplied graphics be XXX dpi, but don't care about the width and height.

SBowie
04-09-2009, 10:24 AM
I'm constantly having this discussion with magazine art editors who don't get it and insist that supplied graphics be XXX dpi, but don't care about the width and height.I hear that. At least in the print realm there is some direct relevance of dpi, to the extent that someone might want to reproduce an image at it's original size with a specified fidelity suited to different print media and requirements.

For video, the relationship is more co-incidental, and not always true. Yet a somewhat related notion has entrenched itself in the collective mind as a kind of a digital urban legend - the 'Video is 72dpi' myth. This can be traced back to an early period where just briefly it was 'kinda sorta' true, for a specific monitor ... but that's where it should have ended.

ted
04-09-2009, 12:07 PM
All true, but we've always found batching to 72 DPI removes the shimmer issue. We only have to turn on SS & HQ if we change the size of the picture in VT-SE.
Those darned Print guys think they own the world! :D

SBowie
04-09-2009, 12:38 PM
All true, but we've always found batching to 72 DPI removes the shimmer issue.Yeah, it's true. It's kind of like if you want to get to N. America from France, you can sail West and you'll be in the ballpark. It works, but only because the target is big enough to allow for a technique that isn't strictly speaking right on the money. :D

As they say, 'close enough for horseshoes and hand grenades'. ;)

ScorpioProd
04-09-2009, 04:22 PM
I never mention DPI in regards to video, since some like to jump all over that as being meaningless! But I agree with you, Ted.

SBowie
04-09-2009, 04:31 PM
I never mention DPI in regards to video, since some like to jump all over that as being meaningless! But I agree with you, Ted.It's not 'meaningless' ... it's just 'misunderstood'. ;)

Rich Deustachio
04-09-2009, 07:19 PM
Well in Photoshop if you use the video preset, it sets it to 720 x 480 72dpi.

SBowie
04-09-2009, 07:38 PM
Sad ... :)