An HDRI is a High Dynamic Range Image. But there is more to it than that. HDRI are used in 3D rendering to create an actual "environment" that provide both the lighting and the reflective properties of the scene.
Now the process to create a real HDRI image goes like this... The image is taken as a combination of pictures where the camera is rotated shot by shot in a full circle and then tilted upwards to capture the sky and then again downward to catch the floor. The upwards shot is called the Zenith while the downward shot is called the Nadir. The nadir can be challenging because certain steps must be taken to remove the tripod from the scene if one is used. So in the case of my camera with a fisheye lens I would take about seven total pictures but bracketed three times that makes twenty-one total images to combine for the fully spherical panoramic image.
Now if you want a really well stitched panorama there is more to just rotating the camera in a circle to take the shots. There is thing called the "nodal point" which is simply the point in the lens where the light pinches off before redirecting towards the sensor of the camera. So basically you don't want the camera to revolve around it's base but rather around the point in the lens, the nodal point. There are certain tripod extensions for this which can range from almost a hundred dollar to many hundreds of dollars.
An HDRI in Action
A photograph that is of high dynamic range is made up of multiple exposures combined into one to create an image that shows the details in the dark areas as well as the light areas more accurately than a normally exposed photograph. This is very useful in shots such as landscapes where you want the sky and clouds as well as the ground exposed correctly without blowing out the sky detail or the ground appearing too dark from underexposing. On my website hdriland.com you can see example of this such as in a church where you want the dark interior to be exposed correctly as well as the bright stained glass windows.This using multiple exposures as called bracketing and most good cameras can do it automatically if set to do so. Some cameras such as my Canon DSLR will create three bracketed images automatically while pricier cameras can do five or even more exposures creating even more dynamic range. Now to make a spherical panorama these exposure must all be stitched together to create the image that when mapped to a sphere will correctly show the full 360 degree scene.
Bracketed Image
Now the process to create a real HDRI image goes like this... The image is taken as a combination of pictures where the camera is rotated shot by shot in a full circle and then tilted upwards to capture the sky and then again downward to catch the floor. The upwards shot is called the Zenith while the downward shot is called the Nadir. The nadir can be challenging because certain steps must be taken to remove the tripod from the scene if one is used. So in the case of my camera with a fisheye lens I would take about seven total pictures but bracketed three times that makes twenty-one total images to combine for the fully spherical panoramic image.
Now if you want a really well stitched panorama there is more to just rotating the camera in a circle to take the shots. There is thing called the "nodal point" which is simply the point in the lens where the light pinches off before redirecting towards the sensor of the camera. So basically you don't want the camera to revolve around it's base but rather around the point in the lens, the nodal point. There are certain tripod extensions for this which can range from almost a hundred dollar to many hundreds of dollars.
This "Nodal Ninja" Panoramic Head Costs Almost Six Hundred Dollars!
But don't be discouraged...I bought my panorama head for like seventy dollars on EBAY and it works great.
Ok so you have your numbers of images it's time to stitch them together and create our fully spherical panorama. There are software programs that do all this but I use one called PtGui which from what I read is the one of the best. When I load the images PtGui automatically knows that they are bracketed images and links them together. Ptgui does a miraculous job of stitching the photos together but if not you have to manually add "control points" to tell PtGui how to stitch the images. This is rare for the regular images but it is essential when trying to stitch the nadir shot to the image. The process can go quickly and sometimes it's quite tedious. But once you are ready you get to do the final stitch for your HDRI that you can use in your 3D programs. You can create an LDR (low dynamic range) Jpg for previewing or of you just want the image to view but you can chose HDR for your HDRI export. Now when you export your HDRI you will get a giant resolution 32bit image in .HDR format, while the jpg is only 8bit. This image can be opened in Photoshop as well as 3D renderers. The results can quite astounding when compared to the 8bit JPG image. You should be able to see the dynamic range of the photo easily. The HDRI can be a massive file sometimes going over 250 MB's. If you want to see an example head over to my site hdriland.com and download an HDRI for free. There are also some short tutorials for once you get your HDRI within a 3D program.
Comments
Post a Comment