Wednesday, December 18, 2013

Creating High Dynamic Range Images with Luminance HDR

Realization came as I waited outside the restrooms at the Charles Russel Museum in Great Falls, Montana. Yes, it felt as strange to me then as it likely does to you reading this now. Fortunately, it had more to do with the relationship of art to photography and tonal values than anything else a person might imagine “realization” to mean.
I was looking at a somewhat recent painting of a grand Montana landscape. I saw clear detail of bark in heavily shaded trees growing in a calm and pretty glen in the foreground. I could see that there was detail in the clouds surrounding a mountain in the background. It was then that I realized the challenges of photography in these kinds of situations that are more easily solved in painting. How do we keep detail in the shadows, prevent bright clouds from being “blown out”, and manage the tones of the overall scene in a realistic manner?

In film photography, contrast can be carefully manipulated through the complex use of color filters to create black and white masks. One of my favorite photographers to use this approach is Christopher Burkett. His work is absolutely stunning and clearly illustrates how photography is art in the manner of controlling all of the tones across the entirety of a vast scene.
For those of us who use digital cameras, there are several software tools specifically designed to help us manage High Dynamic Range images. Such software holds the promise of helping a photographer reveal shadow detail, while retaining highlight tones and pleasing tonal values across a scene. A popular application is Photomatix. It's not too expensive, yet, being a strong advocate for Open Source Software, I used something called qtpfsgui.
At some point, the qtpfsgui project was re-energized with new software developers and the name was changed to Luminance HDR. It was then that the application became rather unstable on my computers. The software would crash when using certain tone mapping operations. I was never able to produce a full resolution Canon 5D Mark II file (5616 x 3744 pixels) without the application suddenly disappearing. So I stuck with qtpfsgui version 1.8.x.

Recently, out of curiosity, I wondered how the Luminance HDR project was proceeding. The software was now up to version 2.3.1. After installing it on my old Windows 7 laptop I quickly saw that much had changed. As I tested the latest version, I realized that Luminance HDR has become a solid, stable piece of software. I can now create full resolution 5D Mark II output files and the tone mapping operations behave in a rock-solid, consistent manner.

I am very happy with the progress that has been made. So, here is an overview of how I use Luminance HDR to process my HDR images.
Step 1 – Capturing an Image
My old Canon 5D Mark II provides a method, called exposure bracketing, to capture a scene in three exposure steps. The ability to over- and under-expose, that is, to set the exposure value (EV) range, is limited to plus or minus 2EV. Still, this is useful for most situations I find myself in.

I use a tripod when making these kinds of exposures in order to keep the three images aligned. It makes the image stacking operations (which we will soon encounter) easier. Many current cameras from Canon, Nikon, and Sony provide in-camera HDR processing, which allow handheld HDR photography, thus eliminating the need for a tripod, unless a photographer finds himself in a dimly lit environment.
In any event, the trick is to capture as much detail in the highlight and shadow areas as possible. This is information the software can use to create a tone mapped image.

Step 2 – Launching Luminance HDR
Starting the Luminance HDR application brings you to a large desktop-like layout. Take a moment to familiarize yourself with the location of the rich selection of operations. To keep things simple, and to show a nicely streamlined process flow, we will use only a few of them here.

Step 3 – Invoking the HDR Creation Wizard
Clicking “New HDR Image”, found on the left end of the tools bar, brings you to an information page which you might find interesting the first time you run the program. Click “Next >to continue to the next operation.

Step 4 – Accessing the Images
The Creation Wizard helps you locate and load your images into the program. Find the big green “+” in the center of the window and click it.

Step 5 – Selecting the Input Images
The image selection window allows you to navigate to and choose the images to be processed. In this example, I have selected three images of the same scene with exposure values of +2EV, 0EV, and -2EV.
If your camera provides an HDR-ready image, select just the single file. All the highlight and shadow information will already be integrated for further processing.

Click “Open to continue.

Step 6 – Viewing the Selected Images
You are now returned to the Creation Wizard window. The list under “Currently Loaded Files displays the names and exposure values of the images that were loaded. The “Preview area shows the currently-selected image.
If you used an older camera that created three separate files, and if you handheld your camera, you will want to select the “Autoalign images checkbox found below the preview area.

Click “Next > to continue.

Step 7 – Passing Through the Editing Tools Window
You will now be in the Editing Tools window. For the way I use the software, there is nothing needing to be done here.

Click “Next > to continue.

Step 8 – Choosing Settings for HDR Creation
There is a selection for “Choose one of the predefined profiles”. The default is “Profile 1”. The various profiles blend the image layers in different ways. “Profile 1 is a very good place to start. In fact, you might not ever use anything else.

I sometimes use “Profile 6”. It blends with a bit of Gaussian blur and produces an HDR image with less noise than “Profile 1”. Still, much of the time I stay with the default profile.

Click “Finish to continue.

Step 9 – Choosing Settings for Tone Mapping
The image is finally ready for tone mapping, which is, for me, the entire point of processing HDR images. It is where the tonal values across a scene are manipulated in potentially visually pleasing ways. This is where the magic happens. If an HDR image is not tone mapped, it will likely look flat and unappealing.

Luminance HDR gives the user a rich variety of options for creating wonderful images. These are the “Operator selections found in the upper left portion of the application desktop. Each operator takes the input HDR image and processes it in its own way. Additionally, each operator has its own collection of parameters with sliders that allow you to further modify the actions of the tone mapping. Exploring the possibilities as they apply to your images is time well spent.
In this example, I have selected the “Mantiuk '06 operator and set the “Contrast Factor to 0.60. I set the Result Size to 5616x3744, which is the full resolution file size of a Canon 5D Mark II.

Step 10 – Initiating Tone Mapping
Press the “Tonemap button, which is at the bottom of the controls on the left side of the work area.

When completed, the tone mapped image will appear in a new “Untitled” tab window on the right side of the work area.

Step 11 – Adjusting Levels
The dark areas of the tone mapped image in this example were too gray for my tastes, so I decided to adjust the color levels by selecting “Adjust Levels from the tools bar to open the Levels and Gamma dialog box. Clicking and holding the tiny left-hand triangle under the Input Levels graph, I slid it to the right to the point where the input level information for the image started. Clicking “OK saved the change and returned me to the Luminance HDR work area.

Step 12 – Saving the Tone Mapped Image
It's now time to save the tone mapped image.

Selecting “Save As from the tool bar opens a window where you can navigate to the desired save location and gives you the field to enter an output filename. The output filename is preselected based on the tone map operators and parameters. You can, of course, change the name to anything you like.
When ready, click “Save. You can now safely exit the Luminance HDR application.

Your HDR image is now ready for processing in GIMP. Here is my final image.

In this example, I took three images of a steam-powered crane with the camera facing into the sun. The three images were underexposed, overexposed, and properly exposed. They were stacked up and tone mapped using the Luminance HDR Open Source Software application.

You can see that the output of the HDR process includes information in the shadows as well as good detail in the clouds surrounding the sun. Compare the Luminance HDR and GIMP-processed file to the original exposures found at the start of this tutorial and you will perhaps see what I mean.
In this way, a photographic artist can create images with as much detail in the highlights and shadows as a painter might paint in extremely high dynamic range lighting situations encountered in the wilds of Montana.


Unknown said...

wow! what a post. Really good. I have learn many things from your post and site. Waiting for your next post.

HDR image editing software

Unknown said...
This comment has been removed by the author.
Unknown said...

Sorry to disagree. It's way too buggy and limited to be used as a professional tool. At least in a Ubuntu enviroment...

Unknown said...

Thank you for your help. This was very helpful!

Alt said...

I know this is an older post, but I can't find a solution to a problem I'm having.
When I try to save an image after I'm done editing it, it only saves at a resolution of 400px across.

I don't know if it's something I'm doing wrong, or maybe I only have a preview version or something, but it's driving me crazy!

I have version 2.3.0

Christopher Mark Perez said...

Alfredo - I've not experienced any bugginess in the installs I've done. Certainly none as bad as when the Luminance folks took over from the earlier developers. Not to say there aren't any bugs, I've just not encountered them. Well, no yet, at least and I've been a pretty heavy user.

Alt - There's a pull-down selection in the tool that allows you to set the output file size. There are several selections. So give that a try (you might have to look around a little to find it) and see if it helps. Note: Depending on the filter, some can change their effect based on the output dimensions.

Alt said...

Thank you for the response! I've since figured out the resolution problem, like you said, but now I'm have trouble with how much it changes after I adjust it! It's altering the image so much it's not worth using... and I don't understand why the resolution would change how the image appears.

But I guess this is built in and not a glitch si complaining won't help.
Thanks again,