Adobe Photoshop CS5 for Photographers - Martin Evening [178]
If you shoot three or five exposures and separate these by two exposure values (EV), this should allow you to capture a wide scenic capture range efficiently and quickly. You can consider narrowing down the exposure gap to just 1 EV between each exposure and shoot more exposures. This can make a marginal improvement to edge detail in a merged HDR image, but can also increase the risk of error if there is movement in any of the individual exposures.
Really still, still life
The Merge to HDR Pro dialog can automatically align the images for you, but it is essential that everything else remains static. You might just get away shooting the HDR merge images with a hand-held camera using an auto bracket setting, but if so much as just two of the pictures fail to register you won't be able to create a successful HDR merge. If you do resort to hand-holding the camera, use a fast motor drive setting, raise the ISO setting at least two stops higher than you would use normally for hand-held shooting and try to keep the camera as steady as possible (hand-holding the camera should absorb some of the mirror shake movement).
HDR file formats
True high dynamic range images can only originate from a high dynamic range capture device or be manufactured from a composite of camera exposures using a method such as the Merge to HDR pro option (which is described over the following pages). Photoshop's 32-bit mode also uses floating point math calculations (as opposed to regular whole integer numbers) to describe the brightness values, which can range from the deepest shadow to the brightness of the sun. It is therefore using a completely different type of image mode to describe the luminance values in an image.
If you want to save an HDR-created image out of Photoshop, you are offered a choice of formats. You can use the Photoshop, Large Document format (PSB) or TIFF format to save an HDR image file. These file formats can store Photoshop layers or adjustment layers, but the downside is the file sizes are at least four times that of an ordinary 8-bit per channel image. However, there are ways to make 32-bit HDR files more compact. You can use the Open EXR or Radiance formats to save your HDR files more efficiently and the Open EXR format will very often be only slightly bigger than an ordinary 8-bit version of an image. The downside is you can't save Photoshop layers using OpenEXR, but this could still be considered a good format choice for archiving flattened HDR images, despite the fact that it is utilizing less of the data than a full 32-bit per channel format such as PSB or TIFF.
How to fool Merge to HDR
Some people have asked if it is possible to take a standard single shot image, create versions of varying darkness and merge these together as an HDR image. The thing is, you can't fool Merge to HDR Pro since it responds to the camera time exposure EXIF metadata information in the file rather than the ‘look’ of the image. However, you can now use Image Adjustments HDR Toning to create a fake HDR look from a normal dynamic range image. The way it does this is to convert an 8-bit, or ideally a 16-bit per channel image to 32-bits per channel mode and then pops the HDR Toning dialog shown in Figure 7.3, which allows you to apply HDR toning adjustments as if it were a true HDR original. Note, this only works if you are editing an image that is in RGB or Grayscale mode and has been flattened first. This isn't true HDR to LDR photography, but it does provide a means by which you can create an ‘HDR look’ from photographs that weren't captured using a bracketed exposure sequence.
Figure 7.3 This shows an example of HDR Toning being applied to a normal 16-bit per channel image (top) to produce the fake high dynamic range effect shown here (bottom).
Merge to HDR Pro
Now that you've learnt what a high dynamic range image is, it's