Always different number of pixels when rendering

[herbieherb]

I made a somewhat strange discovery while developing my ExportImages script. It's that Vectorworks always produces differently sized images when rendering raster images. Most of the time, this only makes up a few pixels. But I still wonder why this is the case and if it can be prevented. For certain images, a pixel-exact export is necessary, if no changes should be visible during later layouts, e.g. in Indesign.

Here's the thread where we found the issue:

 

 

Edited June 24, 2020 by herbieherb

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No response from anyone at VW?

 

I don't suppose anything has changed, as far as this problem is concerned, in VW2021?

[Andy Broomell]

No change in 2021.

 

As far as I can remember, this has been an issue since the day I started using Vectorworks.

 

 

Edited October 21, 2020 by Andy Broomell

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@Marissa Farrell you offered some help on @herbieherb's original thread about the image exporting script that this is related to. Are you able to offer any insight here?

 

This strange behaviour really causes some quite big problems when pixel-exact re-renders are needed. If there was any way around it, it would save a lot of pain.

[Andy Broomell]

I want to link this thread here as well:

 

 

[Andy Broomell]

For clarity, I think there are two distinct issues:

1. Viewports often render pixels slightly different from one rendering pass to another, particularly around the perimeter of the viewport where the rendered pixels are offset slightly and inconsistently from the viewport's crop.
2. Exporting the rendered pixels of a viewport is messy (i.e. impossible) as described in the thread linked above.

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6 hours ago, Andy Broomell said:

For clarity, I think there are two distinct issues:

1. Viewports often render pixels slightly different from one rendering pass to another, particularly around the perimeter of the viewport where the rendered pixels are offset slightly and inconsistently from the viewport's crop.

 

I've a feeling (would need to double check) that it's not just the pixels that change but somehow the underlying image will be very slightly compressed or stretched in the X or Y direction. In other words, you can't even resolve it by cropping the troublesome perimeter area out of the resultant bitmap.

[Andy Broomell]

Indeed, I have encountered that too, which becomes a pain the butt when compositing in Photoshop. 

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I don't suppose there's been any progress on this in the meantime?

 

My workaround had been to re-render a bunch of viewports in one pass, if i needed them all to match pixel-for-pixel.

 

However VW seems to have a new behaviour where it will now sometimes freak out and crash if I ask it to render multiple viewports in one go.