08
High Dynamic Range Images
by Tom ·
Often, to make sure I get the correct exposure, I will take several bracketed images of the same scene. Take a look at these three images I made during a visit to Mission San Juan Capistrano:
The one on the left is exposed the way my camera thought it should be. Notice the lack of detail in the shadow areas and the complete washout of the sky. The center image was taken at the same time but underexposed by 1.5 stops. It shows the blue in the sky and even a few clouds. We don’t often get clouds in Southern California, so we want to make sure they show up when we do. The right image was overexposed by 1.5 stops. If you look carefully, you can see some the beams in the ceiling of the colinnade. Our job now is to take these three images and combine them into one image that shows the elusive clouds AND the woodwork in the ceiling of the colonnade.
One way to get detail in all the important places in this image is to load all three versions into Photoshop, choose HDR from the File:Automate menu, and merge the three 16-bit images into one 32-bit high dynamic range image. This works well and is a great feature of Photoshop. I have trouble with it, though. Since a computer monitor cannot display all 32 bits of dynamic range and my printer cannot print 32-bit images, I have to compress the image back to 16 bits. Photoshop does this for me (go to the image menu, select mode:16 Bits/Chanel) and it will allow you to have some control over the compression process, but it takes more experience than I have to get the detail I want in the places where I think detail is important.
So I use layers and masks to do the deed. As with the HDR automation, I open all three images in Photoshop. Then I copy the underexposed and overexposed images onto the normally exposed image. Make sure your focus is on the image you want to copy, select the entire image (ctrl-a on my PC) and copy it (ctrl-c). Then focus on the correctly exposed image and paste the clipboard into it (ctrl-v). The new image comes in as a new layer. Repeat this for the other image. Now you have one Photoshop file with three layers, the properly exposed background layer, an overexposed layer and an underexposed layer. Right now only the top layer is visible. Select the top layer and make a hide-all layer mask. You can either do this in the Layer menu or hold the alt key and click the mask icon at the bottom of the Layers pallette. Do this for both the imported layers.
Now you should have a properly exposed background that is completely visible because the over- and underexposed layers are masked out. Click on the overexposed layer’s mask, select the brush tool and set the color to white. I generally use a fuzzy brush with about 30% opacity and 30%-50% flow. Then paint (with the mask selected) the areas that you want to make brighter. They will start to appear as you lighten the mask that is hiding the darkest areas.
Then go to the underexposed layer’s mask and do the same for the areas that are too bright in the background. If you make a mistake, either go back in the history pallette or make black the foreground color and paint over your mistake. By varying the size and hardness of your brush, you can have absolute control over the areas you want to lighten or darken. You can also use curves or levels layers to tweak the different layers or the composite image.
I tried this with the three photos above. Here’s the result:
The sky is probably a little more dramatic than I would make it for a print. I wanted to make sure you get the idea.
Have you used this technique? Do you prefer some other technique? Leave a comment and let me know.
Tags: Photoshop
June 23rd, 2008 at 7:43 am
What if you have an image that has washed out or dark areas, but you only made one exposure? If you set your camera to capture RAW images, you’re in luck. Just use your RAW conversion software two times, one with the exposure control set to give detail in the shadows and once to give detail in the highlights. Then combine the two in Photoshop just like you would if you had made bracketed exposures. RAW captures are wonderful because they give you flexibility on exposure and color during processing. If you capture using JPEG format, everything is set when you click the shutter and you can’t change it later without losing information in the image.
June 23rd, 2008 at 7:56 am
As I was playing with this image after I wrote about it, I discovered that using the magic wand tool to select areas to lighten or darken works well. I set the tolerance to make sure the entire area I wanted to adjust is selected. By unchecking contiguous, I was able to select and adjust all the dark or light areas, not just the ones I could paint over. After you have the area you want to change selected, invert the selection (ctrl-I) because you will be using it as a mask, load the inverted selection (select menu, load selection) and make a mask for the bright or dark layer you want to let show through. It will look pretty bad. So use the Gaussian blur filter on the mask to feather the edges until it looks good. Finally, open the blending options for the layer and move the blend if sliders to make the photo look great. You’ll probably get better results if you split the sliders to feather blend.