Diagonal stripes on overlay transparency

[jparnold]

I am currently creating a movie of a recent trip and I have overlaid a map and set Chroma Key and set the similarity to 11% to mask out the background. After rendering I noticed that there are diagonal stripes of light green over the darker green.
What has caused this and what is the method to ensure that I don't get these diagonal lines.
Here is a screen shot to illustrate

[sjj1805]

Did you scan the map. If so those are moire lines
see http://www.dpreview.com/learn/?/key=moire for an example.
Another example here:
http://www.scantips.com/basics06.html

You have to use the de-screen filter on your scanner to eliminate the effect. It is something to do with the printers saving ink and only printing half of the paper - your eyes don't see the missing ink but as can be seen from the above examples, it is revealed when scanned.

[jparnold]

Thanks Steve,
Yes I did use a scanner and I also scanned it at 600dpi as I originally intended to use pan and zoom. I am at present rescanning at 150dpi )which results in an image with resolution of the 'native' 1024 x 576) to try and get around the problem. Maybe I will also try setting the 'region' (during scanning) as a colour drawing rather than a colour photograph.
I will check out the links you suggest and see if I have a de-screen filter on my scanner but I cannot ever remember seeing it.

[sjj1805]

There will be a descreen option in your scanning software, you just have to find it. If the software has a help file you might be able to do a search.

[jparnold]

I cannot find descreen (or de-screen) anywhere including the HELP.
I also checked the HP web site which shows the de-screen feature but NOT for my model.
I have an older scanner (HP Scanjet 5200C).
Do you have a nice simply map of scotland?

[sjj1805]

I shall be home in a hour and will sort one out for you
or you could try
http://maps.live.com/

[jparnold]

Thanks Steve,
I have found some maps including at maps.live - I think I am ok now.