Xlars wrote:
Question: In the simple case that I just want to convert a wide format panorama image to HDRI (the image is a nomal photo with some sky and some ground in it). What do I need to do to convert this into a usable HDRI, lighting my scene with a dome of imagebased lighting? (I know about opening the file and saving as a .mxi in Maxwell Render, but what do I need to do to the image to make it correct spherical HDRI?
Thanks
You have two problems and they should be treated separately:
1) the wide format panorama that you mention, could be a simple planar photograph, or in the best of cases a 360 degrees panorama.
If it is a 360 degrees panorama you have the first problem solved, but in case the photograph you have is just a picture with a FOV angle that is not 360 degrees, you will have to convert it to 360 degrees first.
If you know the picture you have, you could know the FOV angle of the lens used, therefore you will know what to do to convert it to 360 degrees.
Lets assume your picture was taken with a lens that have a 45 degrees horizontal FOV angle. This means that you sees only 1/8 of the 360 landscape. The best solution is going to the site and take the 8 pictures you need. But let´s suppose you cannot do it. One way could be editing the image in photoshop in a way that you could repeat your landscale 8 times horizontally. This new file has 360 degrees in the horizontal plane.
Most panoramas spherical are 1 to 4. eaning the height is 1/4 of the width.
This is that way because 360 degrees is 4 times wider compared to to the 180 degrees that the image has to cover in height.
So, you should increase canvas and fill the sky and the ground with a realistic image.
Now you will realize that it is not that easy. Most of times it is easier to create a panoramic image in a software like terragen, and perhaps add the photograph as part of the visible landscape.
2) the second problem is more difficult than the first.
In order to learn how an HDRI is created you should go to the HDRShop site and read all the procedure.
There is a fake way to convert a jpg to HDRI but you will not get the rtesults you expects as enviroment and lighting.
That way is easy you open a jpg in maxwell and save as HDRI or MXI
It can be done with HDRShop too, open any file and convert to HDRI, but all this is totally fake.
The real procedure is much more complex and would be more or less this way:
3) how to create a spherical HDRI for lighting
Read the HDRShop site
4) how to create an HDRI for lighting and background: buy a spheron camera and you could do it.
Another way would be buy a panoramic head and a digital camera with a wideangle lens, with the correct fov angle. Lets assume your camera sees 90 degrees, then you will need two rows of 4 images to cover the full sphere, but some overlapping is needed, so you will have to do it with at least 5 images per row in 3 rows.
This means 15 images.
But to create 15 HDRIs you will need about 15 images per eaach position.
This means 225 images perfecty calibrated and ordered to be procesed into a stitching software into 15 diferent spherical panoramas, that should be proceces all tgogether into HDRShoiip to create a single Spherical panorama in HDRI format.
This is virtually impossible since there is no time to take 225 pictures in the right order, in a reasonably time so that the scene will not change the lighting.
5) The easiest way is to create a virtual landscape and save a panoramic image in HDRI format like using terragen.
I hope this answer your question.
Ernesto
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