HDRI, Equirectangular Images, 360 degree panoramas, and Poser scenes

My personal notes and observations

Summarised in an Adobe Spark video which I uploaded to Youtube.

Making Equirectangular Images for 360 backgrounds

Introduction:

Equirectangular images are useful for mapping onto full skydomes (of the appropriate geometry), to provide a 360 background in 3D CG scenes. Additionally, if the software permits mapping HDRI versions of the equirectangular image, the image can be used to cast light on the scene without need for adding virtual lighting.

For clarity, I should mention that panoramic images which are now easily created using smartphone cameras, will map correctly onto cylindrical 3D geometry, but not to full 3D skydome geometry. Only an equirectangular image will map correctly to a full 360 skydome.

And for added clarity, I should add that an HDR image is not the same as a 360 image, terms which are often loosely used and conflated with each other in CG. An HDR image (or HDRI) is a tone-mapped image and the format itself actually contains several bracketed images (in real-world photography, a series of images with different exposures). The HDRI lights the 3D scene. A simple Jpg or Png does not contain this information. A 360 image is an equirectangular image, ie, an image which maps correctly onto a full 360 geosphere (discussion of correct sphere geometry to use, is outside the scope of this discussion), and is used to provide background imagery in the 3D scene. So, ideally, one wants to use a HDRI which is equirectangular for one's full geosphere skydome.

Modifying a non-equirectangular scenery image into an equirectangular version:

Software I use: GIMP and Clip Studio Paint EX

Let's just focus on getting 360 equirectangular images done for this discussion (not the HDRI part).

There are several legitimate image resources such as FexyPano, Pixabay and Pexels. When looking for images, try to select scenery taken with the camera's landscape orientation mode, and with the horizon approximately midway of the image.

I use GIMP to work on the first part of this editing process. Because equirectangular images must be width twice of height, the first thing to do is change the image size to those proportions. Then apply Filters | Distorts | Spherize . In the Spherize pop-up window, change Mode to horizontal. Save the image with a different filename. (For this example, I use JPG format for convenience).

I use Clip Studio Paint EX for the next stage of this process. Create a blank new image in the equirectangular proportions (for this example, say 1200 pixel width and 600 pixel height). Next I import the image from the GIMP procedure.

Import | Pattern From Image, then under Tool Property, make sure the Tiling is set to Reverse, the Tiling Direction to Horizontal; uncheck the Keep Aspect ratio, and set the Scale Ratio W value to 50. Of course it looks weird, but at least it is equirectangular and the horrid seams are made less obvious.

Sometimes, the distortion is so great, that it is best to also set Scale Ration H value to 50. Then move the result to the upper half of the image. (In this case, the image will only map the top half of your 360 geosphere but there is no severe distortion). Save the resultant image.

END Of TUTORIAL

Here is my Adobe Spark presentation on this approach, which I uploaded to YouTube.

Using HDRI 360 image on Cycles Root Surface of Geosphere

This discussion is for Poser Pro 11

Various 360-image casting light in Poser scene

I rendered WhiteMagus' cityscapes using Daz Studio Pro's spherical camera, with image dimensions of width and height=2x width. I used the resultant 360 equirectangular images in Poser, applying them to a spher geometry. The 360 image casts light into the scene in Poser. Here I show various 360 images I used to cast light, and how the scenes look when rendered in Poser. I am using the Pauline figure and my own clothing and clothing textures.