Image Exposure 101

February 26, 2018  •  Leave a Comment

I have been asked on numerous occasions how I get the colour into images that I post online. Do I enhance? How do I get the particular look I am after?.

As photographers whatever the scene before us, whatever has caught our eye, be it a particular composition, a Sunrise or Sunset, one thing to bear in mind is the given dynamic range of the sensor you'e trying to capture the image with. If the sensor does not have a large dynamic range, you will not be able to capture the shadow detail whilst preserving the highlights. Larger sensor cameras, DSLR and Medium Format systems have a larger dynamic range. The problem with the exposure rerading that the camera makes, is that it tends to be biased toward the brighter part of the scene, usually the sky. The downside to this bias is that it will leave your foreground underexposed. Most modern sensors can cope with some changes to alter the dynamic range during post processing, but at a sacrifice of leaving some shadow noise to deal with.

So how can you maximize the dynamic range (the ability to capture shadow detail as well as highlights) without losing one or the other. The following images will give you some idea of the steps you can take to get an image that will give you the optimum exposure detail to able to undertake your image enhancement.

My usual way of capturing a wide dynamic range scene IE a bright sky with cloud detail, is to use a graduated ND filter. By using a filter like this, it allows you to preserve the Sky details, whilst keeping the rest of the scene correctly metered. Here are some examples of this.

So in the shot above, I established my composition, using the suggested meter reading I captured the shot, while my Pentax made a good fist of the exposure, it left the sky overexposed thus losing some detail in a quite glorious sky.  I already knew that this would happen, and I would have to do the following, either use an ND grad filter, or by creating a series of images of differing exposures then create a blended image. What would be the reasons for choosing the latter?

One thing about an ND grad is that it will lower the exposure for everything that is within the graduation, my filter are 150mm and the gradient goes from the top down to halfway, so the remaining 50 percent of the filter is clear. This is all fine and dandy if you are shooting a scene like a seascape where you have a nice perfect horizon, but using it anywhere else can cause exposure issues if anything other than the sky sits within the gradient, such as this lovely Silver Birch tree.

The above image had a 1 stop ND grad filter applied, you can clearly see that the shadow detail in the vegetation is preserved, whilst the filter starts to preserve the sky. The red outline is where the grad was used

Using the 2 stop ND has shown the sky details but its starting to block the detail in the tree from being shown.

 

So finally a 3 stop filter ND filter is applied, The Sky has become darker, however the level of detail in the highlights is very much improved. The drawback is how the hill behind the tree has almost no detail, and has turned quite dark along with the tree.

 

The alternative method of getting a nice balance exposure on an image, is to bracket the exposure, most cameras have this ability, and will be within the menu system of the camera. I shoot in manual so the easiest way for me to do this is to choose the correct aperture for the depth of field required, and the correct shutter speed to preserve the details in the image, if it were a windy day for instance, and I was using a slow shutter speed then some elements of the image may blur. So the way I shoot in manual is to shoot a normal exposure one where the camera indicates it's correct. Then shoot one image over exposed, and one or two images underexposed. I usually don't bother going anything above plus one, you can do, but my preference is just the one shot over.

 

You can clearly see in this image that the highlights are blown, but the shadow area beneath the tree contains much more detail.

 

In this shot, the sky detail is being preserved but the shadow detail is being sacrificed.

 

Perfect sky, but no shadow detail retained in the foreground.

 

So with these 3 exposures chosen I can then blend these in Lightroom using the create HDR option, HIgh Dynamic Range. There can be negatives associated with using this technique, which I will cover at the end.

Here are the blended 3 images. An image that retains both highlight and shadow detail. Which is much easier to work on with fine-tuning and sorting out the various aspects of the image that you want to highlight, or bring out.

 

Please bere in mind when shooting your exposures for HDR, that if you are shooting during a windy day, then each frame you take may have some cloud movement during the exposures that have to be dealt with by the HDR algorithym, and may produce some image ghosting. Each method has poitives and negatives, it's whatever you prefer to do in your image workflow.

If you start your editing and enhancement process without a correctly exposed image which should have a broad dynamic range, then any adjustments you make can have in some cases a detrimental effect on other parts of your image. Having a good balanced image, is not only good practice, but by doing so you give yourself the best opportunity to enhance the image as you want. This especially applies to large prints, as any defects will be magnified.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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