Making an HDR image


Published on May 8th, 2009

In my last post about the Rails End Gallery I mentioned that I would do a little tutorial on HDR imaging. There are many tutorials on this subject but I decided to produce a short one as well. It makes a good read and not everyone does the process the same. I am also assuming you know a little about photography so I won’t be explaining all details within this tutorial in great depth. If you want more information, more than I have provided here you can find some links at the bottom of this tutorial.

High Dynamic Range Imaging

HDRI or HDR stands for High Dynamic Range imaging. HDR imaging is the process of blending 3 or more images into one to produce an image to how your eye would see it in real life. Dynamic range refers to the range of brightness levels that are present in a scene. This would be from the darkest shadows to almost featureless black and then up to the brightest whites but before it’s featureless white. In photography and your camera, these levels are measured in stops or f-stops.

Notice the sky is overexposed. This shot was taken under some trees so it was a partially shaded area.

Notice the sky is overexposed. This shot was taken under some trees so it was a partially shaded area.

Now if you were to try and photograph outside using no filters whatsoever on a nice bright sunny day and your in a shaded area, lets say under some trees like the image above, the foreground scene of trees would most likely be exposed properly but the sky on the other hand would be overexposed. This is the same with any other scene where a large amount of dynamic range is present. Your camera cannot capture all of this. This is where HDR imaging comes in. To capture the large dynamic range present in some scenes you need to gather more than just two images of that scene or subject. Read on and you will see what I am talking about.

What You Need To Take HDR Images

You need a computer of course! I assume that you are reading this from your own computer so your already on your way. It will need to be a fairly fast computer as in for processing speed, and will need at least 512MB or 1GB of RAM. This is because when you shoot the images and the program processes them it takes a lot of computing power.

Also you will need a camera that takes some good photos. The camera model I use is the Canon EOS 40D 10.1MP digital SLR camera. A wonderful semi-pro/consumer camera. Yes there are larger models out there but you can do great photos with the new point and shoot cameras as well and smaller consumer SLR models. It is preferred that it shoots in raw file format. Most point and shoot cameras shoot in .jpeg format but some of the newer models are now capable to shoot in raw as well.

The reason for taking photos in raw over .jpeg format is because when you take the image in the camera, it immediately saves this image file to the memory card with no in-camera processing. If you shoot in .jpeg the camera applies in-camera editing to the image file and you lose some of the image data. Also when you combine .jpeg images for use as HDR you can sometimes make the image worse by worsening the artifacts caused by .jpeg compression.

You will need a good sturdy tripod to mount your camera to. The reason for this is so you don’t move the camera too much when you take the differently exposed images. The software program that blends the photographs together can align the photos but not if they are too much out of alignment. So with that said, you will need a shutter release cord as well. If you don’t have one don’t fret, you can use your camera’s timer. Just don’t bump the camera when it’s taking the photographs. All of this is so you keep your hands and any unwanted movement away from the camera. Movement gets exaggerated through the lens.

Next you need some sort of image editing program like Adobe Photoshop. I use Adobe Photoshop CS4 but there are earlier versions out there still. If you use another program to edit images make sure it can edit the raw file format. Then next comes the HDR (High Dynamic Range) program for processing your HDR images. I use HDRSoft’s Photomatix Pro for my HDR processing but there are other programs out there as well. Adobe Photoshop CS2 and CS4 also produce HDR images but I will be using the Photomatix application for this tutorial.

Setting Up Your Camera

Fig.2. The camera modes dial Basic Zone and Creative Zone.

The camera modes dial Basic Zone and Creative Zone.

First, you will need to set up your tripod. Set it to the height you want for your scene and set the camera to take either landscape or portrait format (lengthwise or vertical). Once your camera is set up make sure it is level. Turn on the camera then set your camera to take the largest photo possible. This is to make sure you have the largest image to work with when you are editing it.

Information window at the top of my camera showing you the different shooting info.

Information window at the top of my camera showing you the different shooting info.

Next set your auto-bracket feature, if you have one. You will want to set it to -1/0/+1 EV or -2/0/+2 EV depending on the dynamic range of the scene in front of you. You can also do this by changing the shutter speed manually but either way you will want the camera to take differently exposed images. Also, make sure that the aperture settings (f-stops) stay the same throughout the photo shoot. If they don’t your image once blended will look blurry. A good setting is from f10 to f22.

Menu screen showing Auto Exposure Bracket circled in red.

Menu screen showing Auto Exposure Bracket circled in red.

Use your camera’s creative zone. This is where P, Tv, Av, M are located. If you have not tried this part of your camera I suggest reading up on the different modes to get somewhat familiar with them and how they work. Set your camera to the Av, or M mode to keep the aperture value the same. Also set your camera’s ISO setting to 50, 100 or 200. Anything higher it will start to get too grainy when you blend the images together. Once that’s all set you can start taking photographs!

Taking The Shots

Photo of the gallery. The exposure value set for this image was 0. It's the base exposure the camera sets automatically.

Photo of the gallery. The exposure value set for this image was 0. It's the base exposure the camera sets automatically.

Hook up your shutter release cord or set your timer if you do not have a release cord then take the shots. Make sure though before you take the set of photos that you turn auto-focus to manual as if you keep it set the camera might focus on something different in every image and that will also produce a blurry image once blended. Make sure your camera, or subject doesn’t move or this will create ghosting or registration errors once blended. After your photos are captured and saved take some more, maybe from a different angle. Keep bracketing the shots. Experiment.

For this image I had the auto-bracketing feature set to -1 EV.

For this image I had the auto-bracketing feature set to -1 EV.

Sometimes you may have to do more than just three images and this is where you will have to change the shutter speed manually. Depending on the dynamic range present in your scene you may need up to 7 or more differently exposed images to capture all the dynamic present. Using your camera’s histogram will show if you have captured everything from the darks to the brights. If you look at the three photographs of the Gallery you will notice the differences in the brightness of the images.

For this image the exposure value was set for +1 EV.

For this image the exposure value was set for +1 EV.

Processing

Once you are done taking photographs bring the whole lot back home and start uploading them onto your computer. Save them wherever you save your other photos and make sure they are easy to find. I have a folder set up to upload them to then I rename the images using Adobe Bridge and put the images into different categories. However you name them is up to you.

Next if you shoot in raw, you can process the whole lot of bracketed images you took of that subject in Camera Raw. You can edit for white balance and sharpness, etc but don’t change the exposure settings. Once the images are all blended they will be brighter and if need be can turn up Luminosity if you want. Once your done editing save them all as TIFF files.

Now open Photomatix Pro on your computer. Next click on Generate HDR image and the dialogue window Generate HDR – selecting source images will pop up. This is where you get those TIFF files you just saved. Select the files and then click “ok”.

The next window will be Generate HDR – options dialogue window. This is where you select the different options for processing your HDR image. The first set of options is the align source images. You can select either By correcting horizontal and vertical shifts or By matching features. The one I use the most is matching features. This will align your images up and then crop the small excess off if there is any or click Don’t Crop if you don’t want the program to crop the image.

The next settings that I will group together are Reduce chromatic aberrations and Reduce noise. I have these two checked off as they help in fixing any major noise in your images and aberrations (fringing) during processing. Sometimes depending on what ISO setting you may have used noise can be compounded by combining all those images together. I suggest leaving these two selected unless you want to do the noise fixing later on in Photoshop.

Attempt to reduce ghosting artifacts is the next setting. Artifacts appear in HDR images when an object has either moved through the frame of the image or moved during your photo session. Blowing leaves and moving water can also cause ghosting but moving water can be pleasing if your shooting waterfalls or rivers. People walking around during the different images can also cause ghosting effects. If you shot three images and the person was moving you will see that person in three different spots in each photo. This is difficult in removing but can be done. It’s best to shoot on calm days and away from the public unless you know how to remove these using Layers in Photoshop. I usually have Background movement selected but depending on what and where you took the photo this is up to you. Select either Background movement or Moving objects/people.

Next select the Take tone curve of colour profile and then push Generate HDR. Once the program is done processing you will get something that will look a little odd. Hard to explain till you see it for yourself but because its a 32 bit image, your computer monitor can’t display it properly. To get the image to display properly you will need to tone map it.

Tone mapping is where the magic all begins of HDR imaging. This is where you get to select the amount of colour saturation you want, luminosity, micro contrast, etc. You will need to experiment with the tone mapping process to get the image you want to show. This is trial and error and more of an experimenting process for you. Try each setting, one at a time to see what effect it has on your image then carry onto the next setting. There really is no right or wrong setting. Some of the settings for me usually changes from picture to picture but I generally select a strength of about 80, colour saturation of 55 and light smoothing on either high or very high. Everything else is per taste. Also if you hover your mouse pointer over some of the setting sliders information about them will pop up.

The Final Image

HDR-00043

The final tone mapped image.

After you have adjusted the settings you want for the desired look, click Process. This will apply all the adjustments you made to your image and after a few seconds, depending on the speed of your machine you will get the final image displayed on your screen. Then choose Save As and save it to your computer. Make sure you save it as a 16 bit TIFF file as you will want the biggest file possible if you want to further process it in Photoshop, and then your done. I hope you will enjoy trying out HDR processing and making some stunning images.

I will be getting a Links page for the many sites that has photography information, tips and tutorials for you to read…usually free. On these sites are information about HDR imaging and how to process the files. Also you can do a YouTube search for HDR information as many photographers have made video tutorial. Three sites you can check out if you have not done so already are HDRSoft’s Photomatix Pro, NatureScapes.net and The Luminous Landscape.


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