[chimerax-users] silhouette scaling and image dimension

[Joel Meyerson]

Hi Tom,
Thanks for the detailed answer. That’s very interesting and makes sense.

All the best,
Joel

From: Tom Goddard <goddard at sonic.net>
Date: Wednesday, April 8, 2020 at 9:29 PM
To: Joel Meyerson <jrm2008 at med.cornell.edu>
Cc: "chimerax-users at cgl.ucsf.edu" <chimerax-users at cgl.ucsf.edu>
Subject: [EXTERNAL] Re: [chimerax-users] silhouette scaling and image dimension

Hi Joel,

  Silhouette width is in pixels, not Angstroms, and defaults to 1 pixel (or 2 pixels on retina displays).  You can set the width in pixels with a ChimeraX command "graphics silhouette width 5"

https://www.cgl.ucsf.edu/chimerax/docs/user/commands/graphics.html#silhouettes<https://urldefense.proofpoint.com/v2/url?u=https-3A__www.cgl.ucsf.edu_chimerax_docs_user_commands_graphics.html-23silhouettes&d=DwMFAg&c=lb62iw4YL4RFalcE2hQUQealT9-RXrryqt9KZX2qu2s&r=JnYzuUa3E5p4u7qrfPzeZV8LIgMpwauz4WIvX7NJIi8&m=K053zQd1VRhfO3CTnJFZzXvNR1SKEcYJBzTP6kBXcuk&s=cw6tzeDcjqzQqvP5RrgvbWgFPlAAtm4Vy8ndHCZ_cpk&e=>

Having this rendering effect in pixels is a bit weird.  It is a graphics post-processing operation on a 2D raster image (an opengl framebuffer) that adds edges where the depth jumps, so it is most natural to do in pixels.  If the width were in Angstroms then it would have to be different width at different depths due to perspective projection so it would naturally be a 3D effect rather than the 2D edge highlighting effect that we provide.

  One idea we have discussed is that if you save an image at a different size than what is on the screen, then it should scale the silhouette edge width by the same factor.  We have not done that.  We may some day.  Surface wire mesh display has the same problem -- mesh lines are one pixel widt.  That cannot easily be fixed because modern OpenGL graphics does not provide line widths other than 1 pixel.

Tom



On Apr 8, 2020, at 6:12 PM, Joel Meyerson <jrm2008 at med.cornell.edu> wrote:

Hi,
I noticed that when I save images in ChimeraX with silhouettes on, the apparent width of the silhouette in the output image seems to scale inversely with the image dimensions. For example, these three commands give slightly different silhouette thicknesses. Images attached.

save ~/Desktop/image1.png width 500 height 500
save ~/Desktop/image2.png width 1000 height 1000
save ~/Desktop/image3.png width 2000 height 2000

Is there a way to have a fixed silhouette thickness in output images? I'd also be interested to know why this happens.

Thanks,
Joel
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