Enfuse/Blend

Many times we are complimented on how “real” outNbout images appear, here is one of our secrets…

Why Enfuse?

Enfusing, or Blending, of images is one of our most practiced technique to ensure a “more complete and real tonal range” to our images. The full dynamic range (or gamma) of a typical landscape scene exceeds the spectral range of digital cameras photo cells, therefore areas of extreme darkness or lightness lose their amount of information (color, contrast, sharpness, detail etc.).  If the exposure is biased towards the shadows then the highlights suffer and visa versa, not to mention the increase in “noise”.  If the photo is taken to satisfy the middle of the road then the image will lack the “real” or “three dimensional” aspect of the original scene.

Today a RAW file from a full frame digital camera can have a 12 stop exposure range, thus making the art of image blending possible as each exposure maximizes the potential of that “dynamic portion” of the final image.  This is also known as “exposure fusion”.

The art of enfusing an image involves taking a series of exposures ranging from extreme dark to light and then within the computer “blend” the images together to render a final image that exhibits an exquisite range of detail from both ends of the spectrum with little or no digital noise. Although the technique is not difficult it does require a certain degree of patience and forethought when taking the initial photographs. Instead of taking many photos and then picking out the best one we typically scout out our locations well in advance to determine the best season and time of day to render the shot.

The Final Blended Image

Enfused from 5 original images. See original images at the end of this post

Enfused from 5 original images. See original images at the end of this post

Click here to see the final image after Photoshop Lightroom tweaks

What is Enfuse?

 

The following is an article written by Andrew Mihal explaining the algorithm details of Enfusing.

Enfuse merges overlapping images using the Mertens-Kautz-Van Reeth exposure fusion algorithm (conference paper PDF). This is a quick way to blend differently exposed images into a nice output image, without producing intermediate HDR images that are then tonemapped to a viewable image. This simplified process often works much better than the currently known tonemapping algorithms.

Enfuse can also be used to build extended depth-of-field images, by blending a focus stack…see our article on the topic of Focus Stacking

The basic idea is that pixels in the input images are weighted according to qualities such as proper exposure, good contrast, and high saturation. These weights determine how much a given pixel will contribute to the final image. A Burt & Adelson multi-resolution spline blender is used to combine the images according to the weights. The multi-resolution blending ensures that transitions between regions where different images contribute more heavily are difficult to see.

Enfuse uses three different criteria to judge the quality of a pixel: Exposure, saturation, and contrast. The exposure criteria favors pixels with luminance close to the middle of the range. These pixels are considered better-exposed than those with high or low luminance levels.

How to Enfuse

Field Technique

Although Enfusing can be accomplished taking hand held photographs the results are far more successful and consistent if a sturdy tripod is used.  Therefore the choice of location and environment make this task a bit easier and ensure the best possible results.

  1. Place the camera on a sturdy surface (hint hint… use a tripod)
  2. Crop the scene in the camera rather than in the computer
  3. Determine the base exposure (base the initial exposure upon the desired F-Stop).  We personally use a hand held incident exposure meter.
  4. Activate the camera Aperture Bracketing mode* (typically 5, 7 or 9 exposures with a 1-stop bracket between exposures)
  5. Activate the slow motor drive setting (if available)
  6. Connect the cable release (if available)
  7. Set the base exposure
  8. Set Image type to RAW or Tiff (no jpg please)
  9. Click the shutter – if using the motor drive then all bracketed images will be taken in rapid succession

Field Tips/Comments
– if no cable release is available then take extra precaution not to move the camera or lens focus/zoom throughout the bracketed exposures
– the least amount of time between the first and last exposure will ensure that there minimal change to the series of images (wind blowing tree branches, subject movement etc.)
– *aperture bracketing mode is important as the depth of field must not change throughout the bracket exposures
– if no tripod is available it is still possible to Enfuse/Blend your images depending on the software used as some have the ability to “align” the images prior to blending. There are times that we need to “align” the images when using the tripod as our subject has “moved” throughout the duration of the field photos
– RAW images will render the best results, followed by tiff’s

Computer/Software Technique

There are a number of software applications available for “blending” the images together.
– Photomatix (http://www.hdrsoft.com/)
– Enfuse GUI (http://software.bergmark.com/enfusegui/Main.html)
– PhotoShop
– LR Enfuse (http://www.photographers-toolbox.com/products/lrenfuse.php)

We have used several of them over the years and found that LR Enfuse, a Photoshop Lightroom plugin, renders the best “real” rendition of the original scene.
The primary strength of this product is there is no need to separately export your RAW images as TIFF’s because Lightroom automatically creates them throughout the Enfuse procedure.  This makes enfusing images efficient and straightforward. The alignment of images was excellent regardless whether a tripod was used or not.  The default settings rendered excellent results. The export options include 8 or 16 bit and a selection of professional color spaces.

If you find that the resulting “blend” is too dark or light then selecting a different subset of original images (biased to either extreme) will allow you to get the perfect image in a short period of time.

Then using some basic PhotoShop or Lightroom Develop Edits you can tweak the image to attain the “real tonal range” of the original scene.

Original Images

2 Stops Over Exposed

2 Stops Over Exposed

 

 

One Stop Over Exposed

1 Stop Over Exposed

Normal Exposure

Normal Exposure

One Stop Under Exposed

1 Stop Under Exposed

2 Stops Under Exposed

2 Stops Under Exposed

 

 

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