>Hmmm, Interresting. I actully just made a LED panel and I'm having some
>problems. When the picture is moving the dots seems to be double (is this
>what you call "seams"). I fount out that I could remove this by setting
>the
>refresh rate down to once per frame. But then I get flickker due to the
>low
>refresh rate.
>What can I do to prevent this when I change the refresh rate?
>And how these special refresh algorithms working?
>Can the problem be solved by double the display buffer, and how?

>Thanks in advance

>   Lars


At a previous employment, we exclusively made custom LED signboards.  The trick
to a smooth scroll is to have each dot of every column or row ( depends on which
way you are scanning), to be illuminated for the same length of time.  My guess
is that you are doing a column scan refresh.  These columns extend from column 1
to n.  When a pixel moves from column 1 in one section to column n in an
adjacent section, that dot will be illuminated for two consecutive scans.  The
visual effect is that characters seem to distort only at the seam boundaries.
The fix we used was some fairly complex rules to "predistort" the characters as
they crossed the boundaries.  It worked fine until you tried to pause a
scrolling message, then distorted characters were visible.  I no longer work for
that company, so I do not have the details on the distortion any more.

If your pixels are doubled across the entire signboard during a scroll, then you
are not moving you characters in memory correctly.  The character MUST advance
one pixel for each refresh field.  If the character advances slower that one
pixel for each refresh field, then smearing of doubling occurs.  Remember in a
scrolling message display the scroll rate determines the refresh rate.  The
faster you scroll, the faster you must refresh and vice versa.  Slow scroll
rates always flicker, its the nature of the beast.

Good Luck

---- Steve