This video is only 800x500, and the jitter's amplitude appears to be one pixel.
On Tue, Jan 23, 2018 at 3:52 PM, Paul Wessel <pwes...@hawaii.edu> wrote: > Seems resolution independent; I've tried up to 4K. Here is a 2000x1250 > MP4 movie, just showing the text HELL. It is especially noticeable for > angles 20-30. > > www.soest.hawaii.edu/pwessel/bug.mp4 >> <http://www.soest.hawaii.edu/pwessel/bug_200.mp4> >> > > On Jan 23, 2018, at 5:59 AM, Bradley C. Kuszmaul <kuszm...@gmail.com> > wrote: > > 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 >> >> >
