A quick Guide to HDR Photography 

This is an introduction to HDR Photography techniques for beginners. I will show how you can create HDR images from multiple photographs using different exposures.The Image above shows a beautifull sunrise taken early in the morning.

A natural look is my goal!

Philippe Schoch

Table of Contents

1 What is HDR?

1.1 Exposure Value and Contrast Ratio

1.2 Color Space

1.3 Conclusion

2 In Practice: an Example

3 HDR Workflow

3.1 What do you need?

3.2 How many Brackets do I need?

3.3 Shooting for HDR

4 Checking the Results

5 Issues

5.1 Misalignment

5.2 Ghosts

5.3 Chromatic aberrations

6 Summary

1  What is HDR?

HDR means „High Dynamic Range“. 

Many people have a wrong idea about what HDR photography really is. This technique is used to achieve a greater dynamic range of luminosity than what is possible with standard digital photographic techniques.

HDR is inspired by reality and more specifically by the human eye.

1.1 Exposure Value and Contrast Ratio

First, let us talk about Exposure Value: 

It is a number that describes an F-Number/Exposure time pair. A difference of 1 EV corresponds to a 2-exposure stop.

Any increase of the exposure value by one equals doubling the exposure, any reduction by one equals halving the exposure.

The human eye can perceive about 20 EV of dynamic range in ideal circumstances. That corresponds to a real-life scene with a contrast ratio of 1.000.000:1. This ratio tells the difference in exposure between the brightest (e.g. the Sun) and the darkest (e.g. deep shadow) point of a scene. 

Contrast Ratio = 2^EV.

The Camera takes pictures with a limited exposure range, referred as LDR (low dynamic range) photographs. The result is a lack of details in the bright and the dark areas. 

Regarding camera's dynamic range (examples):

➢ A Canon 5D MK IV has a dynamic range of about 12000:1

➢ A Nikon D750 or Nikon Z6 has a dynamic range of about 22000:1 

➢ A Sony A7III has a dynamic range of about 26000:1 

The advantage of HDR is to be able to represent many levels of light intensity in an image. To do this, several shots of the same scene must be taken with different exposure times (bracketing). The goal is to darken the bright areas and to brighten the dark areas to retrieve the details. 

1.2 Color Space

Typical HDR images contain more bits per pixel than conventional images and allow a much higher dynamic range to be stored. They are stored in 32 bit/pixel (e.g. Radiance or OpenEXR).

However, you maybe also know that it is not possible to display a real HDR photo on a typical monitor without a special conversion step known as tone mapping. Primary purpose of tone mapping is limiting luminosity of HDR image so it fits in the range that monitor is capable of displaying correctly. The tone-mapped image becomes LDR image (Low Dynamic Range). 

LDR pictures are stored in 8-bit bit/pixel (e.g. JPEG) or 16-bit/pixel (e.g. TIFF).

1.3 Conclusion

HDR is in fact a trick, something allowing us to overcome limitations of current devices. It uses photo with much wider luminosity range and it maps it back to the space, which is possible to be displayed on our monitors.

2   In Practice: an Example

In this photo, I have chosen to expose correctly for the highlights. You can see the detail in the sky but the shadows are black.

In this photo, I have exposed correctly for the shadows. Now you can see the shadow details, but the sky is white. 

Here is that photo again, except that this time I have edited it so that the dynamic range better matches that of a screen. To do this, I brightened the shadow detail and darkened the highlight detail.
This is pretty close to the limit of what my camera can do.

Now I have taken 5 brackets and combined them in a HDR Software. As you can see, there is a bit more micro contrast in the image.

3   HDR Workflow

The most important thing in HDR photography is the quality of the bracketing. Good images at the beginning of the process give you a good HDR result.

Do not try to make a bracketing hand-held, you will have too much shakes and the HDR Software will not be able to handle this correctly.

 3.1  What do you need?

 Well, it is very simple:

➢ Camera that has AEB.

➢ Tripod (very important).

➢ Shutter remote control to avoid vibrations.

3.2  How many Brackets do I need?

The number of images required to cover dynamic range of a scene varies from place to place. However, those images should cover as much luminosity as possible from the brightest to the darkest parts of the frame. 

Sometimes 3 shots will do sometimes 5, 7 or even more. Of course, the number of images depend on the EV spacing between the shots of the sequence but most popular steps are 1.0 and 2.0 EV. Ok, so you might ask whether you should choose 1 or 2 EV spacing?

Using 1 EV gives smoothest tonal gradations. That is what I recommend! 

Below there is a table with some of the most common types of scenes and number of exposures needed to properly capture them.

3.3  How to do

Here is the workflow:

➢ File format: Shoot RAW!

➢ ISO: as low as possible to avoid noise and to have a maximum of dynamic range (I use the sensor base ISO, e.g.100). 

➢ White Balance: fixed value (e.g. Sun or 5500K). It has no impact on a RAW file, but all the brackets will have the              same value.

➢ Set your shooting mode to manual.

➢ Set your exposure bracketing (e.g. 1EV).

➢ Set the number of shots.

➢ Choose a fix aperture depending of the scene (>8 for landscapes).

➢ Choose a scene and check the focus. After that, set your focus to manual (or use back button focus), you do not want the focal point changing between shots. 

➢ Check for the right exposure of the scene that will be your 0EV.

➢ Start the AEB

4  Checking the Results

Now it is time to check your Histogram

For the most underexposed shot, the histogram should look like this:

It is well away from the right side. In fact, it should be beyond the middle. You may think this is too underexposed, but experience shows that the best practice is to underexpose by too much rather than not enough. There can be areas that are extremely bright but too small to register. It is better to play it safe.

For the most overexposed shot, the histogram must look like this:

Because it is pulled away from the left side (after the first quarter), you can be confident you have captured detail in the shadows. 

Regardless of how many shots you took, these are the only two histograms you need to check.

5  Issues

The HDR-World is not perfect, there are some issues:

5.1  Misalignment 

The vertical and horizontal movement between the shots of the bracketed sequence. This can cause issues with photo alignment. 

To minimize this movement it is necessary to use a sturdy tripod and to use remote shutter release as mentioned before. 

5.2  Ghosts 

The next issue I would like to mention here are ghosts. 

Ghosts are caused by the subjects moving between shots: people can walk a few meters, the grass blades are waving, the water is flowing… In fact, you can do nothing against ghosts, but some HDR software like Photomatix will fix this problem.

5.3  Chromatic aberrations

Wikipedia:

“In optics, chromatic aberration (CA) is a type of distortion in which there is a failure of a lens to focus all colors to the same convergence point. It occurs because lenses have a different refractive index for different wavelengths of light (the dispersion of the lens). The refractive index decreases with increasing wavelength.”

Putting it simply chromatic aberration manifests itself as color fringing. Unfortunately, the HDR Software increase this effect during tone mapping. I would suggest to correct the chromatic aberration before loading the files in the HDR software. You can use Camera Raw for example to edit the files, than export them in 16-bit TIFF.

6  Summary

The HDR technique is a strong tool to manage extremely high contrast like sunsets or interiors. 

However, it is not necessary to make every picture in HDR. The sensors of modern cameras have a high dynamic range, so that you can cover the luminosity range of most of the scenes.

In which cases you shouldn’t use HDR:

➢ When a scene has a low contrast, you do not need to do HDR.

➢ For silhouettes. A scene where you actually want part of your image to be clipped. This is the antithesis of HDR.

➢ “Fix” an image or to make it better. You cannot take a bad image and make it into a good one by using any processing technique, HDR included. 

My advice is that if you enjoy doing HDR, as the processing part of it and final look – then do it. Think about a good picture recording at the beginning: that is worth it.

Use it as a tool in your photography arsenal, not on every image and every scene.

Philippe Schoch