Saturday, July 29, 2006

HDR Tutorial

Ok, here we go. In response to the multiple requests that I have received for HDR info and tips, I figured I would write a brief walkthrough of the HDR process, some of the tools used and a few tips that I have found helpful.

HDR or High Dynamic Range imaging is a process whereby multiple exposures taken at different light levels are blended using special software into a single image that harnesses the best of each of the individual shots to produce a composite image that is more akin to what the human eye sees when it views a scene.

It allows for the deep shadows and intense bright light to be filtered out of an image, and as such tend to produce some remarkable images.

As for the process itself, there are a few different methods. I have played around with most of them and tend to find the 3x method the best. It involves taking 3 individual images (you can take more 5,7, etc but I find 3 seems to work just fine) of the same shot with multiple exposure values. You then blend these images into a single shot using software specifically designed for this purpose.

The best way to capture these images is through the use of a tripod (camera shake is your worst enemy here) and the Auto Exposure Bracketing setting on your camera.

A tripod will make your camera rock solid and eliminate shake, but also means you have to carry more with you so there is a tradeoff there.

The Auto Exposure settings can be found on most higher-level point and shoot cameras as well as all prosumer and above DSLR’s. Your manual should tell you how to adjust these settings. Once you do, you can set the AE values and the camera will do the rest, which relieves a lot of the headache of adjusting the values manually. More info on this can be found here.

The last trick that I suggest is the use of the timer function or a remote trigger. Things even as little as a shutter press can make the difference between a perfectly composed HDR and one with a bit of blur.

I personally like to use Photomatix:

Currently it is the most popular HDR software out there, and for good reason. It is easy to use and produces consistently beautiful results.

Post processing from there is up to your personal discretion. I use Photoshop and Gimp to clean up my images if there is something that needs done, but for the most part most of my stuff goes straight from Photomatix to Flickr.

Other Methods:
There are other methods for HDR images, and depending on the situation, they may work better for your needs. The option of converting a single RAW into a HDR image is a nice one and provides the photographer the option of capturing things in motion whereas the 3x process would only produce blurry images. This process involves capturing the image as a RAW file with your camera and then in post processing using your RAW conversion software to create 3 individual images with different exposure values (High, Medium, and Low). And then using the same process mentioned above to create the finalized image.

You can also convert directly from RAW to HDR in the automation settings in Photomatix, however I find this process creates tones that are not nearly as natural as can be achieved doing it the other way.

Panoramic HDR:
Panoramic HDR is something that I have recently discovered and have been playing with.

I am currently using a traditional 3x HDR process where I use Photomatix to create the individual images.

I process the first image to where I want it settings-wise and then I save the setting as an .xmp file. That way I can apply that same exact setting quickly and easily to each subsequent image.
I then use Panorama software, to stitch the resulting HDR images together. This seems to work pretty well and makes for some stunning looking panoramas.

I hope that helps a bit and gives you a brief tutorial on HDR. Please stop by my Flickr site , and if you have any other questions please feel free to drop me a line and I will be more than happy to assist you if I can.