Particles looks different when rendered at high resolution

[high-spite]

Hi Dr Sassi and all,

I'm having an issue with the particle system that I need advice on please.

I have custom objects within the RS tag that make the glitter. When rendered at lower res it has a different look to the high res where the particle look a lot smaller and the streak effects look different too which is not what I want

Is there something I'm missing?

[Dr. Sassi]

Hi high-spite,

Without knowing the project settings,

Here is my short demo:

The resolution you provided shows a 1:10 ratio, which means for a 2D object that is a hundred times more pixels in the hi-res than in the low-res. (I rounded your 1460 to 1500 for clarity.)

The energy (light) that a single pixel has in the high-res version, if no post effects are applied, can't grow over one pixel. It creates one pixel.
The energy (light) that a single pixel has in the low-res version, if no post effects are applied, can't grow over one pixel. It creates one pixel.

However, in the low-res version, that pixel has an area that is a hundred times larger. It will show different if both images are shown side by side in the same size.

This is the short explanation. Anything else, I need the file, reduced to the problem.

If it is larger than 1MB, then it can't be attached here as a C4D.

Please use a cloud service, but for security reasons, I will touch only Wetransfer, Google, Dropbox, Apple, or Adobe. Please paste the full URL into the text, no HTML wrapper. The file uploaded as c4d, no compression, no zip, and surely no rar. Sorry for the long request.

All the best

[high-spite]

This post is deleted!

[high-spite]

Hi Dr Sassi, I think I know what you are explaining. Is the way to counter this to simply make the particle size bigger or any other method?

I've uploaded the file to dropbox along with a render at 1500px and one at 9000px for reference.

https://www.dropbox.com/scl/fo/3sdf80lo0c7al2lh27bgc/AKAGuVTsgQwtf5pNEEvjB3Y?rlkey=vpbweac86hqxx38hnjdn5aoj3&st=cif4crdn&dl=0

[Dr. Sassi]

Hi high-spite,

Thanks for the file.

There is no comparison to an image that has 36 times more pixels to define the result.

You might explore the Filter and Filter Size.

https://help.maxon.net/c4d/2025/en-us/Default.htm#html/VPRSRENDERER-REDSHIFT_RENDERER_TAB_SAMPLING.html#REDSHIFT_RENDERER_UNIFIED_FILTER_SIZE

Explore which filter provides you with a better result.

Explore oversampling. Meaning using 9K and going down to 1.5K as defined below:
To do that in one step often harms the outcome.
If you need a single image only, render in 9K and then set the Image resolution in Photoshop twice: first to 4500, then to 1500 (Photoshop> Image Size> Resample Preserve Details 2.0). You may also use three or four steps to scale it down.

In the black frame the downsampled image from the download, as described above.

Another point is the limitation of 8-bit/channel, which doesn't allow good downsampling, as the energy that you might have is gone. Some of your particles have values way above 100% or 1.0. This energy is visually absorbed (based on less contrast) to a certain degree with Bloom and Strike.

You have Bloom and Streak enabled as post effects, both baked into the render and applied as 8-bit/channel only, which will surely contribute to the problem.

Consider adding that later, not on the render directly (baked in), and use 32-bit/channel float (OpenEXR, Tiff, or PSD can handle this.) Later go to any format you need. During production I suggest avoiding 8bit/channel strictly.

Let me know if that works for you.

Cheers