Creating a High Dynamic Range (HDR) Image


I have to say that when I was at Photoshop World Boston in September 2005, I was surprised at how many people asked about the new Merge to HDR feature. I think what surprised me the most is the fact that so many people were interested in it even though the photos contain a dynamic range that exceeds what most printers, displays, and humans can interpret. Nonetheless, it is a speed-related feature and I think it's at least useful to know how to use it.

Step One

First, you'll need to shoot several versions (actually two or more) of your photograph with different exposures. See your camera's instruction guide to find out how to do this. The nice thing about using this new feature in Photoshop CS2 is that it's not limited to only those professional SLR cameras. Most of the basic point-and-shoot cameras also have settings for changing exposure.

©MATT KLOSKOWSKI

One note of caution before you start, though. Many people have tried to fake multiple exposures inside of Photoshop. They then try to run those images through Merge to HDR and it just won't work. Sorry to be the bearer of bad news, but I'm just trying to save you some time.


Turbo Boost

As cool as HDR may sound, there aren't many monitors that can display these types of photos. Because of that, my speed tip here is to not spend too much time creating them because you really won't be able to show them off.


Step Two

Next, select the photos in Bridge and choose Tools>Photoshop>Merge to HDR. Photoshop will think for a moment (or a few moments, depending on the size of the photos and your computer's speed) and then display the Merge to HDR dialog.

Step Three

Here's where you can make a few adjustments based on your desired image output. First, you can click the checkbox under each image to preview what your final image will look like. All you really need to use Merge to HDR is two photos. This option gives you a good way to figure out if your final image will look better or worse if you don't include more images.

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Try not to use your camera's auto-bracket feature to create HDR images. The exposure changes are usually too small and the automation may not even run.


Step Four

On the right side of the dialog, from the Bit Depth pop-up menu, you can choose what bit depth setting you'd like to use. For the best quality possible, and to create a true HDR image, choose 32 Bit/Channel. It's possible to use the Merge to HDR command to save the merged image as an 8- or 16-bits-per-channel image. However, only a 32-bits-per-channel image can store all the HDR image data; 8- and 16-bits-per-channel images will begin to lose some of the dynamic range that you'd use Merge to HDR for in the first place.

32-bit images have a very limited number of tools and functions that can be applied to them. It's good to be aware of this, as when you're back in Photoshop you'll likely see most filters and adjustments grayed out and you won't be able to use them.


Step Five

Next, you can adjust the slider under Set White Point Preview to set the white point. Honestly, the default setting here usually works best, but feel free to experiment. Then, click OK and Photoshop will do the merging for you. Don't worry, your originals won't be harmed. Photoshop will merge the images and open a brand new image in a new document.

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You can use the Merge to HDR command to save the merged image as an 8- or 16-bits-per-channel image. However, only a 32-bits-per-channel image can store all the HDR image data, so there's really no point in using a smaller bit depth.


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You can also use Merge to HDR on scanned photos. The only trick is that Photoshop will pop open a dialog asking you for the exposure settings used when you took the photo, so make sure you know them ahead of time.




Photoshop CS2 Speed Clinic
The Photoshop CS2 Speed Clinic: Automating Photoshop to Get Twice the Work Done in Half the Time
ISBN: 0321441656
EAN: 2147483647
Year: 2006
Pages: 113

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