Basic HDR Effects


What is HDR?

HDR (or High Dynamic Range) is defined as: “A lighting procedure designed to emulate the way that light levels in the real world vary over an enormous range.” In other words, the pictures you take on your digital camera capture the light at the particular instant you take the shot. This could be referred to as an LDR shot (Low Dynamic Range) and although looks fine, with a bit of processing, can look a whole lot better. HDR tends to bring out detail that previously wasn’t visible and adds a certain depth to an image.

There are two methods which can be used to create a HDR image. In each case, to process and create the end result, you need a total of three pictures which differ from each other in exposure only. The exposure of each image will depend largely on the content of the shot, but as a rough guide, use -2, 0 and +2.

Taking Three Individual Shots

Using this method, you will invariably get a better quality HDR image with less noise. If your camera has the capability of setting automatic exposure brackets, use this method to obtain your three images at -2, 0 and +2 preferably in RAW or TIFF format.

If your camera does not have the automatic bracket exposure feature (most compact point and shoot cameras tend not to have this), it’s not a problem. You will simply have to generate the images manually.

Generating Three Images from a Single Shot

– Take your picture as normal – try to get the cleanest shot you can – noise becomes a problem using this method.

– Using a suitable image editing software package (e.g. Photoshop), create two extra images with a + /- 2 exposure setting. In Photoshop CS2, this can be found under “Image > Adjustments > Exposure…”

– You will now have three photos which, to the eye, look like they have been taken at different exposures. The problem lies in that when the HDR generation stage is carried out, the software reads the EXIF data from the image files (information about the image based on the original camera settings). Since all three images you have were generated from the same original, they will all appear to be of exposure 0 to the software.

– To overcome this problem, use any freeware EXIF stripper to remove this information from your images. This will force the HDR software to read the images at ‘face value’.

Here are the images I ended up with for this example:

Exposure -2:

minus2

Exposure 0:

0

Exposure +2:

plus2

It is now time to create the HDR image.

Method 1:

This method involves using Photoshop to Automate the HDR generation process. This method gives good results, but is not all that customisable. In Photoshop CS2 select “File > Automate > Merge to HDR” and then select the images you created or shot and the software will do most of the work for you. Double check the exposure settings and make any changes you like to the end result.

Method 2:

This method yields a similar result to Method 1, but allows more customisable effects. It is done using software called Photomatix. Again, open the three images in Photomatix (“HDRI > Generate HDR”) and verify the auto detected exposure settings are correct. The program will then display a preliminary HDR output.

You can now tweak the end result slightly using “HDRI > Tone Mapping”

In this guide, for the example used, I used the following settings:

– Luminosity: 5
– Strength: 75%
– Colour Saturation: 65%
– White Clip: 4.310%
– Black Clip: 1.310%
– Light Smoothing: Medium
– Microcontrast Level: High
– Microcontrast Smoothing: 0

But feel free to experiment with your own settings to get a result you like. The end result I achieved with this example was:

HDR

Final Words:

This article is intended to be a rough and ready guide to creating basic HDR images. The example photos used are not of a particularly high quality but serve to give you a rough idea of what to expect. You can use any combination of methods in the LDR and HDR stage and have a play with the effects and settings – particularly the tone mapping in Photomatix.
If you do have a play, feel free to leave comments or questions here or post your results over in the forum. Higher res versions of the photos used in the guide can be made available through the forum if the request is there.

Remember I’m no photography expert!!!


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