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photo enhancing -

increasing the dynamic range

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    increasing the dynamic range

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index
high dynamic range [HDR] photos
how the enhancement software works
the photomatix software
abelard.org test-drives photomatix
how to do it all, including exposure blending
examples of tone-mapped high dynamic range images

 

high dynamic range [HDR] photos -
too dark in here and too bright out there, impossible to photo: no longer

“Increase the dynamic range of your photos.

“If you have ever photographed a high contrast scene, you know that selecting the correct exposure will not avoid blown out highlights and flat shadows.”

Original image before digital reworking. Image credit: © 2003-2005 Jacques Joffre Improved image before digital reworking. Image credit: © 2003-2005 Jacques Joffre
Original image before digital reworking.
Image credit:
© 2003-2005 Jacques Joffre
Improved image before digital reworking.
Image credit:
© 2003-2005 Jacques Joffre

There are several other ‘worked’ examples on this page.

There are many finished example images at Flickr: the linked page shows examples and provides many links to more images.

how the enhancement software works

This FAQ page explains the principles and the process used to make pictures like the right-hand one above.

“Tone mapping algorithms scale the dynamic range down while attempting to preserve the appearance of the original image captured. Tone mapping operators are divided into two broad categories, global and local.

  • “Global operators
    Map each pixel based on its intensity and global image characteristics, regardless of the pixel's spatial location. An example of a global type of tone mapping is a tonal curve.
    Global tone mapping is OK for processing 12-bit sensor data but usually does not produce photographically pleasing images when applied to 32-bit HDR images. This is because all pixels of the image are processed in a similar way, regardless of whether they are located in a bright or dark area. This often results in a tone mapped image that looks "flat", having lost its local details in the conversion process.
  • “Local operators
    Take into account the pixel's location in the image in order to determine the appropriate scaling for this pixel. So, a pixel of a given intensity will be mapped to a different value depending on whether it is located in a dark or bright area.
    Local tone mapping requires looking up surrounding values for each pixel mapped, which makes it slower (memory access is the major speed bottleneck on today's computers) but tends to produce more pleasing results (our eyes react locally to contrast). If correctly done, this results in an image preserving local contrast as well as details in highlights and shadows, as shown on those examples.”

In other words, having taken a number of photos of the same view, but with different exposure times, the best exposed parts of the different photos are melded together to make a well-lit final picture. The result can be so highly defined that is reminisant of some Pre-Raphaelite paintings, such as those by John Millais.

The Woodman's daughter by John Evrett Millais, 1851
The Woodman's daughter by John Evrett Millais, 1851

the photomatix software

The software to do this melding, is called Photomatix. There is a free trial version to download, or

“Photomatix Pro is a stand-alone program that runs on Mac OS X and Windows 98/Me/2000/XP. The Tone Mapping tool is also available separately as a plugin compatible with Photoshop CS2.

“One license for Photomatix Pro costs US$99 or €79. One license for the Tone Mapping Plug-In costs US$69 or €55.” [order page]

Lead from Limbic

abelard.org test-drives photomatix Four GoldenYak(tm) award

While the software insists that you feed two photographs to it in order for it to do its magic, in my view this is not the best way to use this software. Here’s what you should do:

  • Take a single image and make a copy with a different name in the same folder.
  • In the “Generate HDR” window, select just those two copies of the same image (the original and the one you have just made).
  • Generate and adjust the image as usual.

This method fools the software into thinking it is using multiple images. Using two separate photographs would require at least using a tripod. As you can see below, the results do not suffer.

This software allows you to create various moods of a single scene/photograph rather similar to the famous series of paintings produced by Monet [eg his Rouen Cathedral series].


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After downloading this program and playing with it, we have awarded the Photomatix software Four GoldenYaks (tm) as one of the most useful pieces of photo manipulation software we have come across. The program is particularly useful for two of our main photographic interests: stained glass, where the light contrast between the windows and the building structure are very great, and macro close-ups of flowers etc, where again there is a great contrast between the surface and more ‘hidden’ background foliage.

Another problem with macro photographs is very low depth of field. With the latest advanced digital cameras, this sort of photography is becoming easy-peasy lemon squeezy compared with the array of equipment and setup times of the past.

This software also has functionality for something it calls “exposure blending” (see the next section).

how to do it all, including exposure blending - the auroran sunset

Below is a worked example using Photomatix’s exposure blending function, then followed by HDR and tone mapping. Note that the software writers clearly did not have this sort of manoeuvre in mind when they wrote it, otherwise the Generate HDR screen wouldn’t baulk at creating an HDR from a single image.

On an earlier trip to Lyon cathedral, before I knew about this software, I tried an experiment: I took one photograph exposed for a rose window and one photograph exposed for the surrounding building. I was hoping that I could later find some way to Photoshop the two together. However, as Photomatix is apparently designed for this sort of thing, I tried that instead.

Lyon cathedral - exposed for the stonework. Lyon cathedral - exposed for a rose window.
original photograph of Lyon cathedral - exposed for the stonework. original photograph of Lyon cathedral - exposed for a rose window.


Step 1: exposure blending

two photos of Lyon cathedral (interior) exposure blended together
two photos of Lyon cathedral exposure blended together.  
  • From the File menu, open the images you want to blend, i.e. the two images above.
  • Next, click on the Combine menu and then click on H&S Detail - 2 Images.
  • A window will pop up. Just press OK [I first ticked the align images before combining box, because as you can see I hadn’t used a tripod].

That gives the first image. My example is to the left. It seems to work pretty well, considering that my original photographs were somewhat overexposed and blurry. Aligning the two images also seems to have worked without trouble.

The Combine menu has four other options. The Average option doesn’t seem to work very well. H&S Detail - Auto, H&S Detail - Adjust and H&S Detail - Sensitive sometimes give slightly better results than the H&S Detail - 2 Images option that I used for this example, but they are fiddly and take longer to render for not much gain.

The most useful of the three is probably H&S Detail - Adjust. Notice the slight ‘painted’ effect on the columns in my version. This seems to be a function of the Radius, which you can set in the window that comes up if you use the H&S Detail - Adjust option. The larger the radius, the more like a painting the picture becomes. You can also set the light level if you use H&S Detail - Adjust, although for some reason the software calls this option, “Blending Point”.


Step 2: making an HDR image

blended Lyon cathedral photo turned into an HDR image
the blended photo turned into an HDR image.  
  • First save your blended image using the File menu. Do this twice, using different file names, so that you can fool the software into making an HDR image from a single picture.
  • Next, click on the HDRI menu and then click on Generate HDR.
  • Click the Browse button and find and highlight the two copies you just saved with your mouse. Click Select, click OK.
  • An Exposure time setting window will come up. Ignore it and click OK. This window doesn't come up if you use images directly downloaded from a standard digital camera. This is because most modern cameras automatically and invisibly encode the exposure information in the image.
  • Then appears the Generate HDR - Step 2: Response curve options window. Leave it set to Use standard response curve (recommended) and click OK.

You now have an HDR image made from the exposure-blended image you created in Step 1. My example is to the left. This gives pretty much exactly what I wanted when I took the pictures (ignoring the blurring of course).


Step 3: playing with tone mapping

blended Lyon cathedral HDR image souped-up a bit
the HDR image souped-up a bit.  
  • Click on the HDRI menu, and on the Tone Mapping option.
  • The Tone Mapping window (see screenshot above) appears, full of weird and interesting knobs and dials.
  • Play! You can watch the results in the preview window.
  • When you are satisfied, click OK.

You now have a tone mapped version of the HDR image you created in Step 2. In my case, I created a rather nice ‘medieval sketch’ which is as ever the image to the left. Notice that my playing seem to have cleared up most of my camera shake along the way.

The images in the first section were created using just Steps 2 and 3.

examples of tone-mapped high dynamic range images

Here are a few versions the auroran sunset made from some of his photographs:

a field - original deliberately under-exposed version
original deliberately under-exposed version
(I took a whole series ranging from over to under exposed, as the tutorials advised!).
 
a field - version adjusted for vivid colours and broody clouds
version adjusted for vivid colours and broody clouds.
 
a field - version adjusted for vivid, but almost natural colours
version adjusted for vivid, but almost natural colours.
 
a field - candyfied version
candyfied version.
 
a field - brighter and less detailed candy-colour version
brighter and less detailed candy-colour version.
 
a field - desolate wasteland version
desolate wasteland version.
 
a field - adjusted version where the colours almost match reality
adjusted version where the colours almost match reality.
 
a field - adjusted version with 'concentric' rings of colour
adjusted version with ‘concentric’ rings of colour.
 
a field - adjusted to look like a snow queen's land
adjusted to look like a “snow queen”’s land.
 
a field - adjusted to look as if a storm is coming in
adjusted to look as if a storm is coming in.
 
a field - adjusted from a deliberately *over*-exposed version of the same shot
adjusted from a deliberately over-exposed version of the same shot.
 
pink flower - my original photograph
my original photograph.
 
pink flower - adjusted for candy-bright colours
adjusted for candy-bright colours.
 
pink flower - adjusted to a darker, veinier type of flower
adjusted to a darker, veinier type of flower.
 
pink flower - now the flowers are dying!
now the flowers are dying!
 
pink flower - adjusted so the background leaves show properly
adjusted so the background leaves show properly.
 
original photograph of me and a friend
original photograph of me and a friend.
 
souped-up version of me and a friend
souped-up version.
 
screenshot of the tone mapping adjustment screen
screenshot of the tone mapping adjustment screen.  

end notes

  1. In photography, the dynamic range refers to the spread between the maximum and minimum measurable intensities of light - the maximum being white and the minimum, black. When you photograph something with very bright areas, as in bright sunlight, or very dark ones, as with deep shadows, the dynamic rage of light can be (considerably) greater than you camera’s handling capacity. An example of such a lighting extreme is when photographing in a dark church or cathedral, where the camera will either record a stained glass window as being too bright, or the surrounding stonework as too dark. This can be exacerbated if the exposure setting on the camera is not precise.
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