What are these weird white specs/lines showing up when rendering with Mantra - Looks fine in Render Region!?

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Hi,

I am a 2nd Year VFX student. I am learning to use Houdini during my summer break so sorry if this is a noob question. I am currently making a scene in which a hallway has a FLIP water Sim falling down the stairs. I am using a Alembic building which i exported from Maya. Anyways, my main issue at the min is that every time i render out the scene, there are weird white specs on the texture of the building (It is just a simple concrete texture, the ones that are pre loaded in the SHOP network. I have altered various settings in the render node, however the problem persists. Any ideas? I am using a set up of a Spotlight, two area lights, an environment light and GILight. It is really confusing me, as when i am using the Render Region Tool, the scene looks fine.

I have attached an image of what keeps rendering out with a rough draft version of my scene.

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flood.1.png (5.0 MB)

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This is with the Concrete texture instead, looks fine in render region (excuse the half rendered image), but again same weird lines and specs appear.

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Screen Shot 2016-07-25 at 20.56.16.png (766.0 KB)

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try setting the sampling quality on the lights to 2 or 3 that might help
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Hi, it has made it better, however i an now getting smaller specks, a noisy image and a ridiculously long render time

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Screen Shot 2016-07-26 at 09.29.14.png (1.6 MB)

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Actually fixed the issue, messed around with the color limit, looks fine now, thanks for the help
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Yes color limit will threshold the specular hits you are getting.

Try replacing the spot point light with a small sphere shape area light say the size of a regular light bulb or slightly bigger. Sometimes the infinitely small point lights (with or without spot light parameters on) may cause these sharp hits.
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I can see that you have Preview on render region turned on.
Disable it and you will get same output as when you render the image.
The preview on usually takes way longer then doing full render. Im not even sure if it ever finish as its refining it self constantly. Useless in Mantra, very useful for arnold.

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