TV Image Glitter

TK
Posted By
Tom Kelly
Nov 10, 2003
Views
287
Replies
4
Status
Closed
I’m using my Canon G2 to show Photoshopped digital pix on my TV. Wherever there’s a strong horizontal contrast line on the image, the TV screen glitters – very annoying! Sharpening an image makes matters even worse.

I read somewhere that there’s a workaround for this. As I recall, it involved using vertical motion blur, but that’s all I remember. Can someone help me with a method to reduce this? Of course, I want to retain all the sharpness and contrast I can.

Thanks in advance.

Tom Kelly
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M
Mr3
Nov 10, 2003
I think what you are seeing is the result of a horizontal line in the image falling exactly on a TV scan line.

Anything that makes the image line span more TV scan lines will soften the effect.

Try Filter/Blur/Motion Blur and set the angle to -90.

Or Filter/Blur/Gaussian Blur.

Explanation:
TV video is composed of frames with 525 scan lines.
Each frame is composed of 2 fields.
Each field is composed of 262.5 scan lines.
Field 1 is composed of the odd scan lines.
Field 2 is composed of the even scan lines.
So a video frame has 525 scan lines separated into two fields that alternately display odd and even scan lines.

If you look at the process in slow motion, you can see why you see the glitter.

First all the odd lines are displayed starting from the top at line 1. Of course this leaves gaps for the even lines. As the odd lines start to fade, the even lines are displayed starting from the top at line 2.

If an image has a horizontal line that falls exactly on one scan line, that image line gets displayed once per frame while the rest of the surrounding image gets displayed twice per frame. This creates that blinking/glitter effect.

Hope that helps

Mr3

"Tom Kelly" wrote in message
I’m using my Canon G2 to show Photoshopped digital pix on my TV. Wherever there’s a strong horizontal contrast line on the image, the TV screen glitters – very annoying! Sharpening an image makes matters even worse.
I read somewhere that there’s a workaround for this. As I recall, it involved using vertical motion blur, but that’s all I remember. Can
someone
help me with a method to reduce this? Of course, I want to retain all the sharpness and contrast I can.

Thanks in advance.

Tom Kelly

TK
Tom Kelly
Nov 12, 2003
Suspicions confirmed; vertical motion blurring is the solution. As Mr3’s response (thanks!) suggests, the glitter isn’t everywhere. It seems to appear only where there’s a high-contrast horizontal boundary. I’d rather not blur the entire image, of course, so I’d like to find a way to select those contrasty portions of the image, and then restrict my blurring to those areas.

Any thoughts on how to do that with reasonable effeciency? I’m using PS
7.01.

Tom

"Mr3"
< &#106;&#104;&#097;&#114;&#114;&#105; &#115;&#051;&#064;&#115;&#112;&#101; &#0
97;&#107;&#101;&#097;&#115;&#121;&#0 46;&#110;&#101;&#116; > wrote in message
I think what you are seeing is the result of a horizontal line in the
image
falling exactly on a TV scan line.

Anything that makes the image line span more TV scan lines will soften the effect.

Try Filter/Blur/Motion Blur and set the angle to -90.

Or Filter/Blur/Gaussian Blur.
MR
Mike Russell
Nov 12, 2003
Tom Kelly wrote:
Suspicions confirmed; vertical motion blurring is the solution. As Mr3’s response (thanks!) suggests, the glitter isn’t everywhere. It seems to appear only where there’s a high-contrast horizontal boundary. I’d rather not blur the entire image, of course, so I’d like to find a way to select those contrasty portions of the image, and then restrict my blurring to those areas.

Any thoughts on how to do that with reasonable effeciency? I’m using PS
7.01.

Set your monitor to interlaced 60hz, or add a second NTSC monitor and set your rez to match. Then select the areas with flicker or dot crawl, and blur away.
—

Mike Russell
http://www.curvemeister.com
http://www.zocalo.net/~mgr
http://geigy.2y.net
B
Brainac
Nov 17, 2003
For the Scanlineprob try Video Filters/De-Interlace.
Its designed to get rid of the scnlienes by moving
every 2nd line iinto thr right place.

regards
Mace

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