HDR and Focus Stacking Technology
Advantages of Using These Methods
What is HDR Processing?
High-dynamic-range imaging (HDRI or HDR) is a technique used in imaging and photography to reproduce a greater dynamic range of luminosity than is possible with standard digital imaging or photographic techniques. The human eye, through adaptation of the iris (and other methods) adjusts constantly to the broad dynamic changes light in our environment. The brain continuously interprets this information adjusting the iris of the eye so that most of us can see in a wide range of light conditions. Cameras, on the other hand, cannot resolve nearly a wide a range of light variation. When shooting photos of an interior of a home it can be very dark in the interior while the light coming through a window will be extremely bright. HDR addresses this problem.
HDR images can represent a greater range of luminance levels than can be captured using more 'traditional' methods. As noted above many real-world scenes contain very bright, direct sunlight to extreme shade. This is achieved by capturing and then combining several different exposures of the same subject matter. Non-HDR methods take a single photograph with a limited exposure range, resulting in the loss of detail in highlights and/or shadows.
The HDR photographer shoots sets of normal, over and under exposed images often referred to as Bracketing. Most newer high end cameras have the ability to shoot Bracketed images. Quite a few have the ability to process and store a HDR image in camera. However, a major drawback of using in camera HDR processing is that with most cameras the images are stored as jpg files, which rules out any post processing of the image. As a side-note, if your photographer is only shooting photos stored in jpg format it is a sure sign they are an armature. Proffessional photographers virtually always use RAW format to allow themselves maximum capability to do post editing of their images.
Unfortunately, many cameras still do not provide adequate Bracketing Range to yield good results in the typical situation one encounters when shooting in a home. Most lower end to midrange cameras only allow for +/-3 EV Bracketing with one normal, one over exposed and one under exposed image. Achieving good HDR results requires at least +/-6 EV, up to +/-9 EV with 5, 7 or as many as 9 images exposed to intermediate exposures. In order to achieve good HDR images I use an external controller with the camera which allows me to expand the exposure range. I post process RAW images with HDR processing software in the computer to provide optimized results.
The image below was shot without the benifit of HDR processing. Note that the view out the window is blown out to the point it is impossible to tell what is outside the window. The darkest areas of the image have no detail and are noisy.
Below is a HDR processed version of the same image. The immediate feature you will notice is that the view through the window of car and house across the street is clearly and visible. Darker areas of the image such as the elephant on the coffee table is more defined to the point you make our features of its face. The colors are more defined and brilliant. HDR photography requires a photographer with lots of experience working with HDR methods. Using improper HDR processing, it is very easy to produce images in which the contrast and colors are over exaggerated resulting in un-realistic looking images. (Note: Focusing in the image below isn't sharp as one would like. See discussion below about Focus Stacking.)
Focus Stacking: What is it and Why Do We Use it?
Why should you use Focus Stacking? When shooting a photograph for real estate, you want everything sharp and in focus from the front to the back of the scene. Setting to an aperture such as f/16 or f/22 and focusing on object at the Hyper Focal Distance away from the camera can help. Often these larger number values of f-stop introduce Diffraction which degrades the sharpness of the image. Many Virtual Tour photographers will use an 8mm to 11mm fisheye ens to shoot their photos. While this type of lens yield exteamly wide Depth of Field, I find a fisheye lens intruduces distortion that makes it difficult to get good seamless stitching of the images resulting in lots of dis-continuous lines in the image. i prefer to use a 14mm - 24mm lens to avoid stitching issues.
If you really want to maximize depth of field and maintain maximum sharpness, Focus Stacking is the technique you must use. Focus Stacking involves shooting several images with lower f-stop values (that doesn't introduce Diffraction) and the adjusting the focus point to several optimal distances based on lens focal length, camera sensor size and aperture. The images are stacked so that objects very near and far-away object are all sharp and in focus. In the example below, proper focus staking techniques were used resulting in the items on the coffee table (nearest) and house across the street (far-away) all being "Tack Sharp" in focus.
The previous image was focused by focusing the camera to the Hyper Focal distance for the lens used. The following image is a HDR Focus Stacked image. In this image you will notice that focus is sharper. The wheel of the car across the street is better focused. The vertical slats on the banister of the front porch are clearly visible on the house across the street. The checkered boarder along the bottom of the window curtain is discernible. The lettering of the books on coffee table are clear and legible. This extra clarity is result of Focus Stacking. A professional photographer understands and knows how to use Focus Stacking for the camera/lens combination he is using. The external controller I use for HDR photography also supports Focus Stacking combined with HDR.