Rendered images look bad, but look fine when using "render region"

[rebar_eater]

I'm trying to produce a basic rendering, but when I render, setting the quality to "best" and using a high resolution, the final results look pretty bad, with visible jagged edges. However, when I render only a portion of the image using the same settings, things look much better. Here an example, showing the two side by side:

A cropped portion of my full rendering:

The same portion using render region:

There's a huge difference, particularly in the smoothness of the mullion lines, despite the two being the same resolution. So why do things look so much cleaner using render region? and is there some way of getting the full image to render with this quality?

[barthbradley]

Why not render region? Sounds like that's the solution here.  Asked and answered. No?  

Help | Define the View Area to Render | Autodesk

[rebar_eater]

Sure, I could do that, but then I have to render my full rendering as a series of smaller images, each taking 30+ minutes to render, during which the computer is debilitatingly slow, and then stitch everything together in photoshop. It's much more convenient for this and any future renderings I do, to be able to set things up, hit render at the end of a work day, and come in to work the following morning to a complete rendering.

Surely this can't be Revit behaving as designed and intended, and something must be going wrong. I'd rather find out what it is and fix it, rather than using a time-consuming workaround.

[barthbradley]

https://help.autodesk.com/view/RVT/2022/ENU/?guid=GUID-0DDD1A6A-8F53-45FF-8BC2-419FBF61500C

[TripleM-Dev.net]

I assume there's a large difference between the region and the full view size?

A smaller portion of the view with the same settings (size output in pixels / dpi) will increase the accuracy of the render. Set the size and/or dpi setting higher, this would normally help.

I haven't used revit rendering personally in a long time, we mainly use plugins for the rendering, so I could be off.

[rebar_eater]

Increasing the resolution doesn't do anything. Both of the images I shared there have the same resolution, the only difference being that one is from when I rendered the whole image and cropped it down to that area, and the other is from when I selected only that region to render.

It's not like it scaled up the resolution of that particular area to match the overall resolution of the full image, it's just that for whatever reason, when rendering a smaller portion of the image, the quality goes up, which seems strange. No other renderer I've used has done this.