It looks like even the straight lines and circles have jaggies, and your
jittering looks like it's just jaggies spread across the time domain. I
don't think you can expect it to look good at such low resolution without
taking a lot more care about anti-aliasing. Can you increase the resolution?
Bradley C Kuszmaul - via snartphone
On Jan 22, 2018 10:06 PM, "Paul Wessel" <pwes...@hawaii.edu> wrote:
> Hi developers-
>
> GMT (gmt.soest.hawaii.edu) is using PostScript to make plots and one
> application builds an animation from sequences of PostScript plots
> converted to PNG with ghostscript (9.22) and then to MP4 with ffmpeg. We
> have found a problem that may be a ghostscript bug, or alternatively we are
> doing something wrong. When using a perspective view (i.e., using a matrix
> concatenation to simulate perspective), the resulting oblique text strings
> "jitter" when viewed as a movie. For an example, see
> www.soest.hawaii.edu/pwessel/bug_200.mp4. As the movie plays, you will
> see the INDIVIDUAL letters in the word HELL jitter relative to each other,
> despite being set via a single show command (here just a snippet of our
> code; setting currentpoint, font etc are omitted here)
>
> (HELL) dup dup stringwidth pop -2 div exch sh -2 div rmoveto show
>
> where sh is defined as
>
> /sh {gsave matrix setmatrix 0 0 moveto true charpath flattenpath pathbbox
> newpath 4 1 roll pop pop pop grestore} bind def
>
> [a complete PS example of a single frame can be found here:
> www.soest.hawaii.edu/pwessel/bug.ps.
>
> At first we suspected flattenpath but HELL (using Helvetica) has no curved
> segments (?). We also tried to override the flattening with 0.2 setflat,
> but no difference. We suspect some sort of roundoff but it affects the
> different letters in the word differently, and that is not under our
> control. Could any of the operators above be subject to round-off that
> affect individual letters?
>
> Perhaps developers know where this may happen and if there is anything we
> can do on our side to remedy the problem. As you can see there is no
> jittering for plotting a circle or lines. The map frame annotations show
> the same jittering so it affects all text.
>
> Thanks for any insight! We can provide more details, all individual PS
> files, etc upon request. FYI, we have tried both tif and jpg instead of png
> but no difference. We also made PDFs and used OS X Automator to build PNGs
> and made a movie using QuickTime Pro; same jittering (not sure if OS X High
> Sierra uses ghostscript in Preview etc).
>
> Paul Wessel
> Lead developer
> The Generic Mapping Tools
>
>
