HDR or High Dynamic Range is the ability to capture the full luminance spectrum of the real-world. This is extremely difficult to achieve and is usually reserved for movies, special effects and some other specialty photography. What’s marvelous about Photoshop, is that you can photograph a subject (multiple times at varying exposures) and then merge the images to create a single HDR image. Here’s how you execute the process…
To make an HDR merge work, you need to take at least three photos of the exact same subject – one for the highlights, one for the midtones and one for the shadows. You should probably take up to six images, just to be safe and to obtain the most data possible. Be sure to use a sturdy tripod so the images can lie on top of each other seamlessly.
Open up Photoshop and choose File > Automate > Merge to HDR. In the new dialog box, click Browse to find and select the multiple images of varying exposure that you took. If you didn’t use a tripod to take the images, you can use the Attempt to Automatically Align Source Images option, but hopefully you used a tripod.
A second dialog box appears with thumbnails of the images that will be combined, a preview of the final result, a Bit Depth menu and a White Point slider. The first consideration to make is Bit Depth, as you’ll want to choose 32 bits to capture the entire dynamic range of your subject. The White Point slider sets the values of the minimum and maximum white level. This enables you to control the overall contrast for the image, as well as controlling the amount of clipping (when the image information is too much or too little to handle). The slider enables you to adjust the image’s exposure to see deeper into the details. Once you click OK (and after processing), you’ll have a single image with the High Dynamic Range that you’re looking for.
The problem with a 32-bit image is that you can’t print it AND maintain the HDR that you just strove for. So what’ll you need to do is convert the HDR image to a 16-bit image. Do this IMAGE > MODE > 16 bit, and you’ll get a Conversion dialog box. But when you do that, you have to adjust the Toning Curve to deal with the clipped shadows and highlights (the range) that is now too wide for 16-bit.
Select Local Adaptation and you’ll get a Curve window, in which you adjust the curve line to reduce the bottom of the output curve in order to bring back the shadows. You’ll need to experiment with the upper and lower end of the Curve in order for this converted image to look as pleasing as possible. And it will, because you’ll have more dynamic range in this one image than you would in any normal single photograph.
At this point you’ll notice that the converted HDR image is lacking sufficient contrast, so again go back in to the Curve and place points on the curve to adjust and refine the contrast to where you want it. Then you’re ready for the final conversion to 16-bit. At this point you’ll have an extremely fascinating image that is properly exposed, but is giving you greater depth of detail in the highlights as well as the shadows.
Before & After HDR Conversion
At the end of the day when you create an HDR image, you create an image in which you’ve added more color information and more contrast information AT THE PIXEL LEVEL. These images push the limits of what you can do with photography in terms of dynamic range… and the resultant down-converted image (which you can make prints from) will be more vibrant than anything you can take in a single photo. As a caution, one must be careful when taking the bracketed images to be used in an HDR Merge where there is a moving subject; otherwise you’ll have a ghost in the final HDR composite image.