A windmill with a painted HDRI background

gsb

Active member
Hello all,

This thread is in response to the question raised in MMounteer's Windmill Model thread < https://www.cheetah3d.com/forum/index.php?threads/14012/ > regarding "painterly" HDRI backgrounds.

Rather than hijack that thread which is focused on their beautiful image with my image, my observations, and any further discussion of using non-photographic HDRI lighting/background, here we are…

Alluvial-Fan-and-Windmill.JPG


This scene/rendering was done rather quickly (using pieces I had previously made for my quiver) to illustrate my answer to the "painterly" question in a timely fashion.

The ocean and all land masses are extremely high-poly models. For what it is worth, only a small part of that overall scene is visible in this image and so the closeup pieces of land could use more polys to smooth out the curves. But that is not important in this context.

The windmill (which is distinctively from another continent and also a high-poly model) was included to provide some, hopefully amusing, continuity to the referenced thread.

On to the point of this post…

The sky is a spherical HDRI I painted in Photoshop. It was used as the source image for a HDRI light with Background: checked.

I would imagine that other pieces of software, perhaps including Affinity Photo, allow for the painting/editing of 32bit HDR images.

In the past I painted HDR images for backgrounds that included objects and land masses. I've moved along from doing things that way for a variety of reasons. One primary reason is the inflexibility in the fixed apparent lighting of a painted background. For my purposes, the tradeoff of enduring slow C3D response times when dealing with 50 some million polygons and triangles is not having to repaint the land on the background whenever I want to change the lighting or when moving the camera around for a different view of things.

To the topic of low or high resolution HDRI for the HDRI Light in C3D…

While I have been using C3D to create models (and test rendering while building a model) for many years, it is only in the past year that I have really started using C3D for serious final rendering. For many years longer than I have been modeling with C3D, I rendered with Electric Image. With new Macs requiring new versions of MacOS, my EI rendering days were drawing to a close with no 64 bit clean EI being released. It was moving on from painting backgrounds with landmasses to modeling the land masses and oceans a year ago that finally forced me to stop rendering in EI. Even though there are many things left behind in that change, the number of polygons C3D can handle leaves EI crashing from lack of memory on my old Mac Pro Cylinder with only 64GB of RAM.

EI provides for the use of synchronized images of different resolutions and bit depths to be used where appropriate. E.g. Low resolution 32 bit HDRI for lighting, high resolution 32 bit HDRI for reflections/refractions, and high resolution 8 bit for backgrounds. All matching spherical ratios.

When I first started using C3D for the final rendering, I continued to use high resolution 32 bit HDR image as the source image in the HDRI Light. I have now switched to using relatively low resolution images for the HDRI Light source image/background.

While, from my experience, I don't think there is a huge difference in rendering times, the memory footprint is certainly lower. And since I no longer include any near or mid-field objects in a background image, only sky and clouds, the low resolution 32bit HDR source images look just fine and dandy. The max dimensions output from C3D is 8192 px square. Perhaps if C3D was able to render a far higher resolution output, a higher resolution sky with clouds might make a noticeable difference.

Again, my work does not rely on a background image for anything but light and sky with clouds. Neither does my work lend itself to using a flat projected rectilinear background plate.

So, this will not address everyone's needs, but hopefully it can be helpful in some way.

Cheers,
gsb
 
Last edited:
Here's my early test. I took a detailed HDRI of a mostly blue-sky sunset into Affiinity Photo and did a find edges before exporting it to a new HDRI. Without the Cheetah objects in the way, the resolution of the HDRI still gets chewed and pixellated in some places - this will be a case where I suppose I would build a lower res HDRI for reflections and use Affinity's Live Perspective tool to build a hi-res backdrop image from a similar camera angle.

2021-06 Filtered HDRI.jpg

2021-06 Filtered HDRI BDrop.jpg

What I haven't found yet is a way to use Affinity to create art styles similar to what I used to do with Photoshop (Stucco, Pointilism, impasto, tiles, etc. ) I used to own a painting program that was pretty good at converting photos into particular art styles, but it died with the Intel Mac transition.

At least the technique seems to work, giving me a way to put more illustrative environment around naturalistic models. That's what I wanted to play with.
 
Hello,

Here are a four renders of a scene, each of which uses a different HDRI as the source image of the HDRI Light with Background: Checked.

While all four renders use a different HDRI for the lighting and background, each of the four HDRIs started out with the same high resolution HDRI spherical photograph.

The source pano is a 32bit 1.3GB OpenEXR file which is 16,792px x 8,396px.

Note how the lighting and look of the models in the scene remain quite consistent across all four renders.

This first render uses the source, full res image.

gsbX-highResHDRI.jpg
 
This render uses a low resolution version of the image. The background is quite pixelated, but the lighting is fine.

gsbX-lowResHDRI.jpg
 
This render uses the low resolution file with some "painterly" filters applied. I make no claim to the aesthetic desirability of the effect, just that it is clearly not a photographic look.

gsbX-lowResHDRI-painterly.jpg
 
This render uses the high resolution file with some "painterly" filters applied. The look is rather subtle. Most Photoshop paint effect filters don't work on 32bit images, those that do, and have adjustable scale, seem to run out of memory, even with a fair amount of available RAM.

gsbX-highResHDRI-painterly.jpg





As is the often the case when trying to give a photograph a "painterly" look, a high resolution source image isn't always the best route to getting there.

Cheers,
gsb
 
Oh and by the way, all four of the above images were rendered in Falcon to only 150 spp at 2048px x 2048px for example purposes.

The render times for all four image was 58 seconds, even though the size of the HDRI files were different.

I downsampled to 50% in PS and exported them as jpegs for posting.

Thanks to Martin for getting C3D to handle 1.3GB HDRI images with total ease.

Cheers,
gsb
 
As I mentioned somewhere else: To get good quality as a background, just use a backplate (if you're talented enough, you could even do a render without your objects and then use the render of the hdri as a template for overpainting ...). But with a normal jpeg you don't have all that trouble and don't have to compromise quality-vise.
 
Hasdrubal wrote
As I mentioned somewhere else: To get good quality…

and this is what he wrote in the Windmill thread < https://www.cheetah3d.com/forum/index.php?threads/14012/ >
Just an aside: (HDRI as background works only well with lower res renders (or very big hdris and wide camera angles). As big as the hdri may be, you only see part of it in the render (for example only 2000 px or less in the width from a 16 k hdri. Such a big hdri would at the same time unnecessary raise the render times. Instead there are hdris (even free ones, for example on hdriheaven) coming with a matching backplate (a high resolution picture as background image). So you can use a 2 k hdri for lighting (in such situations even less would work; meaning "fast") and still have a believable situation with the background (though that's of course depending on the quality of the pair). In this case one could change the backplate into something painterly)

Hello,

Yes, there are many things to consider when choosing a technique to use for a background of a scene. Whether or not an HDRI as a background works well, for anything, may not seem to be quite as simple as "it only works well for lower res renders", but it is pretty close to being absolute… depending on one's definition of low resolution.

That said, and anyone's talent aside, the desired result of any effort goes a long way to helping determine what techniques are best used.

E.g. if one is animating a camera circling a static object, it seems that a spherical HDRI background might be a far better choice than a flat background plate.

With that in mind, Hasdrubal's general observation about only a small part of an HDRI Light background image being seen at any given time in a scene is absolutely correct. If one is rendering a 4096px wide image, using a camera with a 45° horizontal view, then only 1/8th of the width of a HDRI background image will be visible (360/45 = 8). To have the background be the same apparent resolution as the image being rendered, i.e. the background won't be pixelated, then the total width of the spherical HDRI would need to be 32,768px (4096 x 8).

If one has determined that a spherical HDRI background is best for the job, and is attempting to create a painterly style of a photograph (or using a painting) for that HDRI, then it might be best to choose a painterly style that does not degrade stylistically when pixelated.

Again, for the most part I've moved on from using background images, be they flat plate, cylindrical plate, or panoramic spheres. The spherical panorama sky/clouds that I paint are what I use for HDRI Light source images with Background: checked. Sky and clouds still look pretty good when pixelated. For the work I do these days, everything else is a model and nothing was ever a photograph.

Thanks and cheers,
gsb
 
Back
Top