All text and photographs © Emil von Maltitz 2010


High Dynamic Range Images – Part II

Tonal blending using layers and masks


IIn the previous article on blending high dynamic ranges images I looked at my personal favourite technique of simply creating large basic selections and blurring the edge of these selection masks to bring through broad areas of tonal value. When done carefully, this technique can mean for very natural looking images that still have tremendous tonal depth. The problem is that for some images these basic masks don’t work. For instance - image have very fine detail that also happen to have a very high tonal range. Here simple selections don’t work and the photographer has to resort to a more complex selection in order to single out shadows or highlights.

It is this style of imagery that the standalone programmes such as Photomatix excel at. Here the tonality of the various images is mapped out in their respective luminance values and then blended together according the range of tonal values that the photographer desires. This is one of the ways in which you can get that ‘HDR look’. I personally am not all that fond of this ‘look’ but recognise that it is a useful tool in the photographers box of tricks. Here is my approach to creating tonal mapped images without the dedicated software (although you will obviously need an editing suite like Photoshop, Elements, Gimp or Corel Paint).

Creating a tonal mask.

The most important part of tonal mapping is actually working out where your tonal values lie. This is actually very easy. Make sure that you have the channels palette open on the screen. Here you will see four different layers: RGB, Red, Green and Blue. Clicking on Red, Green or blue channels turn the image into a greyscale image relating to the respective channel. Hitting ‘ctrl + left click’ hereafter referred to ctrl + click) selects that channel (you will usually see the marching ants appear). If you ctrl + click the RGB channel you select all the tonal values that are brighter than 50% grey. The beauty of the selection is that it is self-feathered. In other words if we were to go into quick mask you will see various shades of mask, meaning that the tones are selected according to their tonal value as well. Creating a mask of this selection would therefore create a negative mask.

highlight layer Shadow layer Base layer

Putting this into practice then:

Step 1 Open the 3 images that you have created your HDR with.

Step 2 Layer them in a stack so that they are optimised for the highlights at the top of the stack (the darkest image), optimised for the shadows in the middle (lightest image) and your base exposure at the bottom (the average exposure). It’s a good idea to auto-align the images so that they match up perfectly. You can do this by going to Edit>Auto Align Layers... and following the prompts on the dialogue that appears. Auto usually works well.

Step 3 There are two ways to go about this next step. Both work, but have subtle differences depending on the image in question. I would recommend trying both and seeing which




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