HDR – Part 1
Here comes a biggie… This is going to be at least a 2 or 3 part entry. Get some popcorn ready because this is going to be interesting.
HDR (aka: High Dynamic Range), is a type of image processing that takes as few as one high bit RAW image and as many as 9 or more bracketed exposures of the same frame and processes the data into a single 32bit per pixel image. Now it is far more in-depth than just taking those frames and squishing it into one file, but I don’t care how that works. Instead I am going to share what to do with it and how to do it yourself. (If you want technical details on it, I will link some articles that explain the technical aspects in depth.)
First of all, because I am an Intel Mac Pro user, I am slightly limited in my software options for HDR processing. Lucky for me the best option for Mac users is one of the most popular for both PC and Mac users. Photomatix Pro is currently on version 3.1.3 and costs about $99 (at the time of this post) for either platform. That price also includes a plug-in for Lightroom 2.x to export images directly into Photomatix and re-save processed images back into your Lightroom library. Sorry Aperture users, the plug-in for you is an extra $79 charge.
Now we’ve all seen the over-processed HDR photos that simply don’t look real at all and the first thing that comes to mind is “Ugh, what the?” Don’t be afraid, that is only their personal taste for processing. You can process the image as realistic or hyper-real as you want later. Personally, I tend to prefer processing mine closer to the realistic end of the spectrum but I will touch on the extreme later as well.
Here is an example of an HDR I created using a 9 shot bracket with my Nikon D300 and my then brand new Nikkor 14-24 F2.8 wide-angle zoom lens. Pardon the subject matter, I was doing this to test how extreme I could get with HDR while keeping it as realistic as possible. The bright daylight pouring into the windows directly in frame as well as the many windows in the bedroom area of the suite was the only light source for these shots. The same results could have been done with fewer shots but perhaps with slightly less detail.
Although I did get a single exposure with the room exposed just about right, no matter what the window was automatically blown out by 2 or 3 stops. On top of that, the corners of the room and other areas in shadow were still underexposed. This is where HDR can really show it’s place in the post processing world.
As you can see above, the HDR version looks as natural as if you were standing in the bathroom (er, sitting on the toilet in fact) gazing out the window into the San Diego morning sky. And I can assure you that the full size version lacks no detail. In fact, it has more detail across areas of the frame that were otherwise under or over exposed in the unprocessed image. Plus since it can utilize the best image data from each of the files processed into the HDR, it can actually reduce noise and other artifacts that would normally be present giving a better overall image than you started with.
Now on to building the HDR file itself…
For a “true” HDR, we need 2 or more shots. (I will cover single shot HDR in another post.) Ideally the bracketed shots should be taken on a tripod to minimize movement and I like at least a +/- 1 stop difference between frames. Starting with Photomatix version 3.x, it can now directly process RAW files so unless you already processed your files out of your favorite RAW processing software to 16bit TIFF and want to start with those instead, go ahead and use the RAW images. (Starting with a 16bit TIFF is very good but one more step in the process that takes time.) The RAW files contain more bit depth and often extra detail that the JPEG out-of-camera simply lacks. (Shh, I don’t want to hear it. Turn on camera raw when shooting brackets for HDR at the very least.) Now go ahead and load your bracketed shots. When loading it gives you the option of “Generate HDR”, “Exposure Blending” and “Open Files Only”. Right now I want to go ahead and use Generate HDR. This will bring up a second dialog box with more options. Most are self explanatory but if you forget, just mouse over the option and it will give a description of what each is for.
Since I do most of my planned HDR brackets using a tripod, I don’t worry about having the software align the images since they should already be in nearly perfect alignment. Although I don’t typically shoot things that move, sometimes an object will fly through one frame or something will catch a breeze. For those situations you can enable a filter that will help eliminate issues with any shots that may have had moving objects but I almost never use this as it slows the process and I have found it doesn’t help much or can even introduce it’s own problems. Otherwise, I do normally have “Reduce Noise” checked but tend to keep “Reduce Chromatic Aberrations” unchecked. And depending on if you are working with JPEG, TIFF or RAW files, some of the options may be grayed out. But for JPEG and TIFF files I typically use “Take tone curve of color profile”, this does not apply when working with RAW files. Now press “Generate HDR” to begin processing your images.
When you click to start the process, depending on the image sizes, how much money you spent on your new Mac Pro last year and how many files you are trying to merge into one HDR, you can go get a cold beverage of choice while you wait. (This can take a few minutes.) One thing I can suggest is while learning the software, copy the images to another folder and scale those images down to about 1000px on the long side first and play with the smaller versions until you get the hang of it. This will save you a lot of time with both processing and tone mapping. Although some of the tone mapping settings will slightly vary with the different scale, most will carry over just fine. You can always save the settings you like on the sample size and re-open the full size files and re-load the settings again to process the full size HDR.
About 5 minutes passed by now and you’ve slugged down a beer or two, you will now see what appears to be…. Yikes!
Of course no display can handle a 32bit file so the software displays it like this. Not to worry, you are not even half way done yet. For the sake of crashing, I would go ahead and save this HDR file with the group of other files so you have it handy for practice and if the software freezes up on you. The next step, Tone Mapping.
HDR – Part 2 is now online.