# Rendering artifact **URL:** \ **Category:** Hardware Questions\ **Tags:** batch, renders\ **Created:** [December 28, 2024, 12:30am UTC](https://forum.logik.tv/t/rendering-artifact/11931 "2024-12-28T00:30:57Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![Fernandovfx](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.logik.tv/fernandovfx/32/4331_2.png) [@Fernandovfx](https://forum.logik.tv/u/Fernandovfx)\ **Post date:** [December 28, 2024, 12:30am UTC](https://forum.logik.tv/t/rendering-artifact/11931/1 "2024-12-28T00:30:58Z")
Hi guys, need help! Fast Framestone, slow storage. Render artifacts (black masks, etc.). Weak NAS or config issue? Running A4500 20GB GPU, latest ![WhatsApp Image 2024-12-19 at 22.35.17](https://us1.discourse-cdn.com/flex020/uploads/thedepartmentofexternalservices/original/2X/9/9af826da00a0ac3a55f43632462fccf002c85c92.jpeg) DKU. ---
**Author:** ![Fernandovfx](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.logik.tv/fernandovfx/32/4331_2.png) [@Fernandovfx](https://forum.logik.tv/u/Fernandovfx)\ **Post date:** [December 28, 2024, 12:33am UTC](https://forum.logik.tv/t/rendering-artifact/11931/2 "2024-12-28T00:33:42Z")
Noting that it’s a 1600-frame sequence in 5K DPX. ---
**Author:** ![AdamArcher](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.logik.tv/adamarcher/32/3529_2.png) [@AdamArcher](https://forum.logik.tv/u/AdamArcher)\ **Post date:** [December 28, 2024, 10:01am UTC](https://forum.logik.tv/t/rendering-artifact/11931/3 "2024-12-28T10:01:16Z")
What colour space are you working in? ---
**Author:** ![Fernandovfx](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.logik.tv/fernandovfx/32/4331_2.png) [@Fernandovfx](https://forum.logik.tv/u/Fernandovfx)\ **Post date:** [December 28, 2024, 10:51am UTC](https://forum.logik.tv/t/rendering-artifact/11931/4 "2024-12-28T10:51:36Z")
Log dpx 12bits ---
**Author:** ![andy\_dill](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.logik.tv/andy_dill/32/15475_2.png) [@andy\_dill](https://forum.logik.tv/u/andy_dill)\ **Post date:** [December 28, 2024, 5:53pm UTC](https://forum.logik.tv/t/rendering-artifact/11931/5 "2024-12-28T17:53:33Z")
Looks like some extreme values in a matte or two mattes being combined via a subtract. Is either of those things happening? ---
**Author:** ![BrittCiampa](https://avatars.discourse-cdn.com/v4/letter/b/ec9cab/32.png) [@BrittCiampa](https://forum.logik.tv/u/BrittCiampa)\ **Post date:** [December 28, 2024, 6:14pm UTC](https://forum.logik.tv/t/rendering-artifact/11931/6 "2024-12-28T18:14:37Z")
Yeah, first place I’d start is with a clamp on my masks ---
**Author:** ![SamE](https://avatars.discourse-cdn.com/v4/letter/s/e36b37/32.png) [@SamE](https://forum.logik.tv/u/SamE)\ **Post date:** [December 28, 2024, 7:48pm UTC](https://forum.logik.tv/t/rendering-artifact/11931/7 "2024-12-28T19:48:31Z")
Not saying this is the OP’s problem, but… If you need a clamp, you probably did something wrong. If you negate, then multiply a matte instead of subtracting, you’ll never have negative values. Also try screening instead of adding when combining to keep the values from going over 1. Better edges are a bonus benefit to these simple techniques. It’s really compositing 101. Shocking how many flame artists don’t have these basic skills. ---
**Author:** ![AdamArcher](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.logik.tv/adamarcher/32/3529_2.png) [@AdamArcher](https://forum.logik.tv/u/AdamArcher)\ **Post date:** [December 28, 2024, 9:02pm UTC](https://forum.logik.tv/t/rendering-artifact/11931/8 "2024-12-28T21:02:28Z")
It does look like a NAN issue to me too, where there is some maths going on that has produced a negative number. Harder to do in Log than in linear but still possible. You want to look through your comp. In a lot of nodes there is an ability to clamp within it instead of adding a clamp node but as Sam suggests, this is a quick fix to correct something. That hasn’t been done properly. Also make sure that none of your footage has been tagged incorrectly in regards to colour space. ---
**Author:** ![philm](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.logik.tv/philm/32/9286_2.png) [@philm](https://forum.logik.tv/u/philm)\ **Post date:** [December 28, 2024, 9:31pm UTC](https://forum.logik.tv/t/rendering-artifact/11931/9 "2024-12-28T21:31:14Z")
@Fernandovfx - Foi uma sessão super divertida, irmão - vamos fazer mais! ---
**Author:** ![ytf](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.logik.tv/ytf/32/109_2.png) [@ytf](https://forum.logik.tv/u/ytf)\ **Post date:** [December 28, 2024, 10:41pm UTC](https://forum.logik.tv/t/rendering-artifact/11931/10 "2024-12-28T22:41:28Z")
I agree it looks like negative values, probably from a comp node set to subtract. If I’m just gmasking out a portion of an existing matte, I do it right in the gmask node with the mask set to outside. ---
**Author:** ![BrittCiampa](https://avatars.discourse-cdn.com/v4/letter/b/ec9cab/32.png) [@BrittCiampa](https://forum.logik.tv/u/BrittCiampa)\ **Post date:** [December 29, 2024, 12:15am UTC](https://forum.logik.tv/t/rendering-artifact/11931/11 "2024-12-29T00:15:22Z")
> [@SamE](#): > > …problem, but…If you need a clamp, you probably did something wrong.If you negate, then multiply a matte instead of subtracting, you’ll never have negative values.Also try screening instead of adding when combining to keep the values from going over 1.Better edges are a bonus benefit to these simple techniques.It’s really compositing 101. Shocking how many flame artists don’t have these basic skills. I’m an unapologetic disciple of the negate multiply and also the screen methods of combining mattes. I believe I learned it in one of your flame FxPHds a decade ago @SamE! ---
**Author:** ![SamE](https://avatars.discourse-cdn.com/v4/letter/s/e36b37/32.png) [@SamE](https://forum.logik.tv/u/SamE)\ **Post date:** [December 29, 2024, 12:51am UTC](https://forum.logik.tv/t/rendering-artifact/11931/12 "2024-12-29T00:51:52Z")
Sorry to jump on your shit @BrittCiampa. ---
**Author:** ![andy\_dill](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.logik.tv/andy_dill/32/15475_2.png) [@andy\_dill](https://forum.logik.tv/u/andy_dill)\ **Post date:** [December 29, 2024, 1:53am UTC](https://forum.logik.tv/t/rendering-artifact/11931/13 "2024-12-29T01:53:16Z")
@BrittCiampa @SamE I love and respect you both, but may I suggest you combine mattes with the comp node’s blue inputs? 😀 It’ll do the invert and multiply, the screen, and every other option you could want, all in a single node! I highly recommend. ---
**Author:** ![marios](https://avatars.discourse-cdn.com/v4/letter/m/f04885/32.png) [@marios](https://forum.logik.tv/u/marios)\ **Post date:** [December 29, 2024, 2:01am UTC](https://forum.logik.tv/t/rendering-artifact/11931/14 "2024-12-29T02:01:29Z")
And if the above don’t fix it,… I’ve seen similar results caused by mblur, try rendering with mblur off in your masks and/or action nodes, … if that works then you need to do some prerenders with mblur on or mblur workarounds ie RSMB, … ---
**Author:** ![SamE](https://avatars.discourse-cdn.com/v4/letter/s/e36b37/32.png) [@SamE](https://forum.logik.tv/u/SamE)\ **Post date:** [December 29, 2024, 2:16am UTC](https://forum.logik.tv/t/rendering-artifact/11931/15 "2024-12-29T02:16:40Z")
Hey @andy_dill, Can you use just the blue inputs? I never tried it… ---
**Author:** ![ytf](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.logik.tv/ytf/32/109_2.png) [@ytf](https://forum.logik.tv/u/ytf)\ **Post date:** [December 29, 2024, 2:30am UTC](https://forum.logik.tv/t/rendering-artifact/11931/16 "2024-12-29T02:30:39Z")
I do it all the time, but you have to remember to hit f4 twice because you’re looking at the matte output. Hitting it just once shows black. ---
**Author:** ![Fernandovfx](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.logik.tv/fernandovfx/32/4331_2.png) [@Fernandovfx](https://forum.logik.tv/u/Fernandovfx)\ **Post date:** [December 29, 2024, 10:53am UTC](https://forum.logik.tv/t/rendering-artifact/11931/17 "2024-12-29T10:53:17Z")
Fixed it! Rendered steps in batch, and VRAM usage dropped from 100% (red) in Resource Manager ![Screenshot from 2024-12-29 07-47-36](https://us1.discourse-cdn.com/flex020/uploads/thedepartmentofexternalservices/original/2X/2/2d8cdfab795235fcd2cfe4bc93ea112d34565c4e.png) ---
**Author:** ![Fernandovfx](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.logik.tv/fernandovfx/32/4331_2.png) [@Fernandovfx](https://forum.logik.tv/u/Fernandovfx)\ **Post date:** [December 29, 2024, 11:02am UTC](https://forum.logik.tv/t/rendering-artifact/11931/18 "2024-12-29T11:02:27Z")
> [@SamE](#): > > …problem, but…If you need a clamp, you probably did something wrong.If you negate, then multiply a matte instead of subtracting, you’ll never have negative values.Also try screening instead of adding when combining to keep the values from going over 1.Better edges are a bonus benefit to these simple techniques.It’s really compositing 101. Shocking how many flame artists don’t have these basic skills. > [@SamE](#): > > …problem, but…If you need a clamp, you probably did something wrong.If you negate, then multiply a matte instead of subtracting, you’ll never have negative values.Also try screening instead of adding when combining to keep the values from going over 1.Better edges are a bonus benefit to these simple techniques.It’s really compositing 101. Shocking how many flame artists don’t have these basic skills. Apologies for not recalling this specific lesson. I have the FXPHD video tutorials and would appreciate guidance on which one covers this topic. Thank you for bringing it to my attention