# I now understand how to stop particles moving in my CT Scan 'model' :)

edited July 2016

I'm starting slowly, with a simple 10 particles in a row, as a cone with no radius, so they're all in a single line.

Then I set the timeshift to -1.0 seconds and set their lifetime to 60s and their initial speed to 400.

Oh yes and I keyframed the particles per seconds from 10 to 0 after 1 frame.

So I have 10 particles that appear instantly and move off together in a line.

But what I actually want is for them to not move at all after they've been created, but even if I keyframe the Movement speed to anything at all, including backwards, after they start moving on the first frame, they ignore it and just keep going.

Same if I change the acceleration or scale. Nothing changes. At all.

I also changed them to a built-in rock shape and that did nothing too. even with the scale set to 1000% and the speed to -4000 after the first frame, it stayed the same size and speed.

What am I doing wrong, how do I get them to not move after they've been formed?

• edited July 2016

Think of a particle as shooting a bullet from a gun. Once the bullet leaves the gun its velocity and trajectory are set and only the forces of nature can change this. These forces being gravity, wind and basic air friction.

In Hitfilm we can simulate gravity and wind with directional forces. Sadly we do not (yet) have an air/fluid friction "force".

edit: also striking an object can be simulated in Hitfilm with deflectors. The friction and bounce properties are how we control this interaction.

• Moderator
edited July 2016

@NormanPCN 's answer is  correct as far as it goes. And it's a pretty good analogy. But he left out the Lifetime panel.

The settings in the control tab change spawn parameters. That is to say, when a particle is spawned it is assigned the values of the current control settings and it follows them

You need the Lifetime panel. (Was it you I did a breakdown of that with?)  Anyway, the Lifetime panel is where you can tell particles how to vary behavior over their life. For example, you could set Lifetime Movement so all particles slow from 100% initial speed to 0%.

There's also a Time Scale parameter. You could change this from 100% on frame 0 to 0% on frame1. This would stop the particles in their tracks.

Or,if you need particles in a line, set movement to zero and keyframe/move the emitter point to drop them where you want.

Another way to create a line would be to create a quad emitter with either X or Y size set to zero, basically creating a line emitter. Set this to Boundary, Grid and set one dimension to 10 divisions, the other to 1--against forcing a straight line spawn at equidistant intervals. With a speed of 0, again.

• Moderator

"Was is you I did a breakdown of that with?"

Uhhhhhhhhhh what?

• Moderator

• Isn't there also a keyframable "Speed" property, or am I shrooming?

• Hi, sorry, was AFK and now it's time for bed, but I'll pick this up tomorrow.

@Triem23 Nope, wasn't me you went over particles with. First time I've played with them. I want to try that solid image from a CT scan thing from that thread a few weeks back, but it's a steep curve as no tutorial shows how to do something remotely like that.

Weird to have keyframing available on the Speed, Acceleration and Scale that don't actually do anything. Unless they work at other times (when?) why aren't they locked to be incapable of keyframing (like Transform properties are in the editor), with a little dot instead of the circle ?

Because otherwise it's a wee bit confoooosing.

• edited July 2016

"Weird to have keyframing available on the Speed, Acceleration and Scale that don't actually do anything. Unless they work at other times (when?)"

They do something. All particle system parameters affect how a particle is created. Once created, only the Lifetime panel can change the particles attributes and all attributes are not available in the lifetime panel.

Once a particle is created they in a sense each have their own independent timeline. That timeline goes from 0% lifetime (creation) to 100% lifetime (death). The lifetime panel is this timeline.

• Moderator

I'll find the breakdown I typed up and re-paste it here.

If you're trying to do something similar to the MRI scan @NxVisualStudio did, I think he used the Time Scale to freeze his particles, but, really it's easier to move the emitter and just use a 0 Speed on the particles to set that up.

The particle sim is probably the most powerful tool in Hitfilm, but it's also the most complex by far. So be prepared to mess around a lot.

Incidentally, the rotating  wireframe building in this shot is built with the particle sim in basically the same way as NxVisualStudio's MRI shot.

https://youtu.be/JoEyTPzgkX0

For the MRI shot Tony set up his emitter to shoot particles in a straight line (point emitter, cone trajectory, 0 radius) and using Time Scale to freeze everything once built. I did the same emitter trajectory type, but had zero movement on the particles and moved the emitter, dropping particles as it moved. To the way I think, it's easier my way, but it's another demonstration of how in Hitfilm there's usually three different ways to do anything!

Now, the other key to building a "3D Object" with the Particle Sim is setting up a layer as a texture source (by, say, bringing all the MRI slices in as an image sequence). You can set up layers as texture sources then decide if you want a particle to be a still frame from that layer or moving video from the layer. For Tony's MRI and my building this means keyframing the source frame of the texture layer so the slices are dropped in the right location to build up the volume. If keyframing attributes in the Control Panel effected particles after spawning, then this trick wouldn't work, so it's also a demo of why the Particle system is set up so "Controls" effects the spawn state of a particle and the Lifetime Panel effects what happens after the particle is spawned.

One more video example: this "80's retro"  3D landscape display is made with the particle sim. A Lightning filter was used in an embedded composite shot to make a slowly evolving bolt. A duplicate of this composite shot was made and a grid filter was added to the lightning to make some moving dots (basically where the lightning intersects the grid).

Both of these composite shots were embedded in in particle sim comp.

There are two point emitters, cone trajectory, 0 radius firing particles towards the camera.

One emitter is using the lighting comp as a texture source. This emitter is creating 6 particles/sec and is making the horizontal lines of the 3D grid. The other emitter uses the "Dots" composite creating 60 particles/sec to create the "vertical" lines of the grid.

https://youtu.be/WuZ_kVNkqBM

• Moderator

Found it. Man, I post a lot here. Took awhile to find. Here on page 2 of Andy001z's thread we talk about the Lifetime Panel a bit with a breakdown of how it works.

http://hitfilm.com/forum/discussion/comment/72811/#Comment_72811

Also, check this thread: in the first post on page 1 Simon listed most tutorials available up till last August. Scroll down to the Particle sim sim listing and look at "Anatomy of a Particle Sim," "Introducing the new Hitfilm 2 Texture System," "Advanced 3D Particle Behavior," "Creating a Clone Army," and, "Advanced Particle Physics" 1 and 2. Those should get you up to speed for anything using image or video textures.

• @Triem23 ; (RHD) Thanks, a lot to go through there and I did look at a few of those tutorials as well as one by @InScapeDigital, but after a while got 'can't see the wood for the trees' blindness.

Also found the blend modes when using an image sequence as the Layer source only has Normal, Add and Multiply. Well Multiply did the same as Normal, so a big black square around the images. They're greyscale .JPGs, so have no Alpha, so I'll have to reexport them as .PNGs after using Demult on them, I guess.

@NormanPCN what I meant was this. where I can add keyframes until I'm blue in the face, but only the initial condition counts, so why is it keyframable here at all if the lifetime panel is where it all happens?

No change at all after the second keyframe....

http://i854.photobucket.com/albums/ab106/pickaname2/keyframe1.jpg
http://i854.photobucket.com/albums/ab106/pickaname2/keyframe2.jpg

Getting dragged out to go shopping so I'll get back to this later.

• Moderator
edited July 2016

Embed the JPG Image Sequence and Demult it to remove the black background.

Keyframing the initial conditions is important, (as always) depending on the shot. NxVisualStudio's MRI shot, my wireframe building and procedural landscape rely on keyframing a start texture frame. I've done shots where a ship crashes and burns out, but I keyframed particles per second, particle scale and particle alpha so the rising smoke trailed off as the explosion ends rather than cutting out.

I have a current sequence where debris emitters have speed,  particles/second and scale, mass and rotation  keyframed so I have an initial blast of large debris chunks from an initial explosion trailing off to fewer, but smaller/lighter chunks continuing to spawn representing crumbling structure around the impact point. In this case the keyframes of the spawn conditions change the nature of the debris. Initial high-speed particles are blown out by the explosion. Later slow speed particles are just falling. Large, high-mass particles have more "inertia" (less pull from gravity) while smaller, lighter particles have less inertia.

The Lifetime panel is set so that each particle slows (representing wind/air resistance) down from explosion velocity while gravity (a force)  pulls things downwards.

• edited July 2016

@Triem23 Ah yes, that would work too, cheers.

Oh yes, I keyframed a few other things, lifetime, set the number of particles to 10 for one frame, then to 0 etc.  That worked as expected, It's just those particular ones in the images above do diddly squat AFAICS.

Which threw me for a loop, because setting the speed to 0 after one frame of setting it to 400 is what I expected to work in the same way, but it's ignored completely and the Lifetime panel is required. I understand (now) once you've shot a bullet it can't be controlled as such, as per Norman's explanation, but don't understand why the interface allows you to do something has no effect. Or I'm misunderstanding that that does interact with the Lifetime panel. Not investigated that yet...

The weird and wonderful world of particles has many avenues to explore...

• Moderator

Lifetime panel controls (except Alpha and Color) are relative to the Controls settings. I.e. if a particle system is spawning with a speed of 100, and you have a Lifetime Speed curve with a deceleration from 100% to 50% particles spawn with a Speed of 100 and slow to 50. If, as the sim runs, you keyframe the Speed to raise to 200, those particles will spawn with a speed of 200 and slow to 100.

So these Lifetime settings are Relative Multipliers of the Controls Value

The Alpha and Color Lifetime Graphs override the Controls values. Alpha and Color are absolute settings.

The interface isn't allowing keyframing of values that do nothing. You are changing the spawn values of particle parameters, which are then fed to the Lifetime graph for modification.

• edited July 2016

Ah, gotcha. It's because I have set the number of particles to zero after the first frame that it has no apparent effect as it's for effecting subsequent particles that are emitted (which Norman actually did say. In bold too...) - which I have set to...none. Doh!

• Moderator

Correct!

Controls define spawn behavior, Lifetime modifies this behavior over life. Time scale modifies the speed of the entire sim.

Incidentally:

A particle SIMULATION is a  LAYER with one, or more EMITTERS.

Each Emitter can have one or more PARTICLE SYSTEMS and/or MOBILE EMITTERS.

A Mobile Emitter behaves like a particle from it's parent emitter, but it spawns it's own Particle System.

Each Particle System or Mobile Emitter, as well as the Particle System spawned from a Mobile Emitter has it's own unique CONTROLS settings and it's own unique LIFETIME settings.

A Particle System can use a photo/video layer, a 3D model or an inbuilt texture to render a particle. Video textures will animate. Animation applied directly to a 3D model source layer will propagate down to each particle duplicate.

All Lifetime settings can be viewed as MULTIPLIERS of the associated Controls values, except for ALPHA and COLOR which OVERRIDE the Controls values.

A Particle Simulation Layer may contain one or more DEFLECTORS that act as obstacles for particles. A Deflector can be a cube defined in the Sim or a 3D photo/video/plane layer.

Each Simulation can have one or more FORCES defined either globally or as a cubic volume within the Sim.

Deflectors and Forces are GLOBAL within the Simulation. Individual Particle Systems or Mobile Emitters can be set to ignore Deflectors and/or Forces, but you can't have "Particle System A" reacting only to "Force 1"  and "Particle System B" reacting only to "Force 2." A either reacts to 1 and 2 or ignores 1 and 2.

Multiple Emitters/Systems in a single Simulation Layer will calculate and render faster in 3D unrolled mode than single Emitters/Systems on multiple Simulation Layers.

Make sense?

• Probably, I'll let you know when I've played about a bit more. Cheers.

• edited July 2016

@Triem23 OK, found time to come back to this again and....got it working fairly well, apart from the actual display quality part.

Lifetime didn't seem to do what I needed, as it was only expressed in percentages and I needed frame level control, so for this, I didn't need to use it at all.

So, instead I keyframed the animation frames to follow a point as they were generated with 0 speed, which stretched them out over 90 frames to get the depth correct for the 'model'. By setting the amount of points to 30 per second over 3 seconds, then to 0, I got the 90 frames I wanted. I can animate the camera around it OK, and it 'works', but I have an issue with the detail.

I moved the images to a comp and added Demult, so they'd show through each other, and in the particle effect, I used Normal, because Add bleached things out too much. But, in order for it to look like a semi-transparent image, I have to turn the opacity of the images in the composite down to 4% or they start to drown each other out. I tried playing with the contrast, but even 100% doesn't have a massive effect at 4% Opacity (before the Demult).

I don't know why the particles only have Normal, Add and Multiply blend modes (Multiply just seems to turn them invisible), when what I think I want is probably Screen.

I tried using Normal as the blend, then setting the Overall Blend type in the Composite Images to various settings, but they either all appear to do nothing different, or go invisible. i.e there is no difference between Add and Normal there, when there is a difference between Normal and Add in the Particle system.

The principle works, in that I can highlight areas on different images in colour and they stand out in the 3D image when it's rotated (apart from side on, when it looks like an open window blind, of course), but I was hoping for more clarity/contrast.

Any suggestions?

Here are a couple of images where I highlighted my knackered shoulder and also, I think, part of my Aorta/Blood Supply.

One image is a Screengrab from Hitfilm (obviously. ) The white version is when I loaded the .PNG into Paint Shop Pro and it crushed the Alpha channel, but weirdly, made the highlighted sections stand out better, so...that's a win.

http://i854.photobucket.com/albums/ab106/pickaname2/shoulder.jpg
http://i854.photobucket.com/albums/ab106/pickaname2/shoulder2.jpg

• edited July 2016

I worked it out.

Using Hue & RGB Key I was able to isolate various sections. The first obvious one was the Red Bloodflow section and the other was the skeleton, which even keying on the green shoulder: I was able to adjust and get to include the rest of the high contrast areas - bones - and include those.

Another layer with the inverse of that key removed the bones and just left the muscle/soft tissue behind.

So with 3 layers: Bones, Soft Tissue, Blood, I was able to adjust the transparencies of each one and overlay several particle systems to get the higher contrast look I wanted.

It just occurred to me that I could also vary the transparency of the skeleton from front to back (the images scan in that order) so that the front ribcage is less transparent than the sides and back so that it obscures the internal tissues less on that final combo shot, although not sure how that would look as it rotated.
Render time went up from 8 minutes for one layer to 45 minutes with 3 and the keying, so I'll try that later.

Edit: Just tried that and realized they should have all been set to 3D unrolled to combine properly, not 2D (which was fine when it was only a single system), for that to work properly - which it now does brilliantly - so long render coming up anyway.

The last image is of the properly 3D combined particles with the more transparent front ribcage.

http://i854.photobucket.com/albums/ab106/pickaname2/shoulder3.jpg
http://i854.photobucket.com/albums/ab106/pickaname2/shoulder4.jpg
http://i854.photobucket.com/albums/ab106/pickaname2/shoulder5.jpg

Proper 3D version.
http://i854.photobucket.com/albums/ab106/pickaname2/shoulder6.jpg

• Staff

That's looking pretty good!

• Thanks.  Once I thought to use multiple particle layers, I can emphasise different parts pretty easily now.

I isolated the heart with a feathered circular mask keyframed to exclude other areas around it as it changed shape over the frames, added some light blue tint (rather than using fill on individual areas of images in a paint program, as I did with the shoulder and blood supply) to make it stand out a little more, then increased the opacity of that layer and put it inside a flesh tinted version of the chest with opacity reduced to 1%. Result: almost solid looking heart floating in a ghostly body cavity.

I've now got better visualisation options of my knackered shoulder than the consultant had.

http://i854.photobucket.com/albums/ab106/pickaname2/shoulder7.jpg

• Moderator

That's looking really good.

Hmmmm... I should find the disc of MY shoulder's MRI data. We can compare injuries. ;-)