In this tenth and final episode of the series on fire and smoke with the Fluid simulator in Blender 4.5, we won’t go through full tutorials but rather share tips and suggestions on how to modify the appearance of fire both during rendering and afterward, using Motion Blur, Color Management, and Node Compositing in post-production.
This tutorial is part of a 10-episode mini-series on the basics of Fire and Smoke in Blender 4.5. For the complete list of episodes, click here.
Video Transcript
Hello everyone! In this tenth and final episode of the series on fire and smoke with the Fluid simulator in Blender 4.5, we won’t go through full tutorials but rather share tips and suggestions on how to modify the appearance of fire both during rendering and afterward, using Motion Blur, Color Management, and Node Compositing in post-production.
We’ll also discuss the settings for rendering fire and smoke in Eevee.
Let’s start with a setting that affects rendering itself, without post-production. This is the choice of Color Management, which is made in the Render tab. In particular, the Filmic mode seems to produce flames with more saturated colors. Selecting High Contrast makes the fire appear more intense.
On screen, I’m showing a comparison: on the left, a render made with AgX, and on the right, one made with Filmic and High Contrast. Color Management affects the entire image, not just the fire, as we can see by looking at the stones at the bottom. In a moment, we’ll see how to isolate and adjust only the flames in Compositing.
Another option we can enable in the Render tab is Motion Blur, which is very useful when rendering these simulations since flames are never perfectly still between frames. In a previous episode, we mentioned that the Domain has a field related to Velocity Scale for Motion Blurring, but Motion Blur must also be enabled at the rendering level in the Render tab. In this tab, the Shutter parameter defines how many frames before and after the current one are taken into account.
Higher values result in stronger motion blur.
On screen, I’m showing a comparison between a render with Motion Blur disabled, one with Motion Blur enabled and the Domain’s Velocity Scale set to 1, and a render with Motion Blur enabled and the Domain’s Velocity Scale set to 10, intentionally exaggerated to highlight the differences. Unfortunately, there’s no magic formula for finding the right value for Shutter or Velocity Scale, since the best choice depends on the needs of your current project. Testing is necessary. Keep in mind that enabling Motion Blur and increasing Shutter or Velocity Scale values will significantly increase rendering times.
For any rendering, the final look also depends on good Node Compositing in post-production.
Fire is no exception, and in this case, we can also take advantage of the Emission Render Pass, which allows us to isolate the pixels of light-emitting sources, such as Emission or Volumetric Materials, for compositing. So, I enable this Render Pass in its dedicated panel before running a test render and moving to the Compositing Nodes editor.
Using the Emission information, which gives us the flames in color on a black background, we can apply various Compositing nodes to improve blur, glow, contrast, or even color.
The result of these operations can then be applied back onto the original render. Blender offers different blending modes and factors for this purpose.
For example, I’ve processed the flames separately, blurring them and adding different types of Glare effects, before applying the result to the original render through a Mix Color node set to Screen.
I’m also quickly testing brightness adjustments using the C channel of an RGB Curves node.
I even try modifying only the Red channel within the same node.
The final result may be a bit too strong, but I can always adjust the Factor value as needed.
I can also disable or re-enable the entire setup by selecting the Mix Color node and pressing M, that is the Mute function, which toggles the node on or off.
Before moving on to the tips for rendering settings in Eevee, let me show you a final comparison of the options we’ve discussed so far. On the left, you can see a render with AgX as the Color Management, without Motion Blur and without Compositing. On the right, you can see the same scene rendered with Filmic set to High Contrast, Motion Blur with Shutter set to 1 and Velocity Scale set to 10, plus a bit of post-production done with the node setup I just described.
OK, now we can move on to the rendering settings in Eevee.
Up to now, I’ve always used Cycles for rendering, but Eevee introduces some necessary differences since its key feature is real-time rendering.
In Eevee, fire and smoke simulations are represented as slices of the scene that are then stacked like translucent sheets. Among the parameters to configure are the start and end points of these slices relative to the observer’s position. The settings that control the quality of the final result are mainly found in the Render tab, specifically in the Volumes section.
The first parameter in this section is Resolution, and intuitively, the closer this value is to a one-to-one ratio, the higher the quality will be. With lower ratios, quality decreases, but render times are shorter.
As mentioned earlier, the viewing volume is divided into slices called Steps. The Steps parameter works together with the Custom Range Start and End options, which are enabled by default. The space between Start and End, beginning from the observer’s position forward, is divided into the number of slices specified by Steps. Each slice is rendered, and the combined result produces the final image. Obviously, we don’t need the default 100 meters, so we can reduce the Start and End values to match the Domain of the simulation and concentrate the Steps within that space to achieve a better result.
These are the most important parameters to understand in this section, especially to explain why simulations sometimes disappear when moving around in the scene!
As for shadows and their quality, in the Sampling Shadows section of the Render tab you’ll find the Volume Shadows checkbox, which is disabled by default. Enabling it allows you to also set the Steps value, which, of course, is tied to the quality of the result.
And that wraps up this final tutorial in the series on the basics of Fluid simulation for fire and smoke in Blender 4.5! I hope this series has been useful to you.
If you’d like to thank me, the best way is to subscribe to the channel and leave a Like on the video.
Thanks, and see you soon!