Extracting Maximum Data From Your Images

The photograph above was taken at an abandoned row of heritage style houses at Bukit Nanas in Kuala Lumpur. The image has a tremendous amount of detail in terms of light, shadow, colour and texture and I think highlights the amount of information or "data" that can be extracted from a photograph (or in this case a series of photographs) to create a final image that is close to what we perceived in reality with the human eye. I wanted to take this image as an example and describe a little of the process I use to extract this information from the raw images and create the final image above.

The Problem

I'm sure I am not alone when after taking a photograph of a scene which captured our attention we are disappointed with the resulting image which did not really capture or show the essence or mood of what we actually saw with our eyes. A scene with subtle colours and perhaps bright highlights or deep shadows comes out as a bland, rather flat image and does not come close to what we originally perceived with our eyes.

The fact is that our eyes can see a dynamic range in the order of 10 to 14 f-stops. This figure relates to a "static" view by the eye (i.e. looking at one area with no pupil movements) whereas in real life our pupils are constantly and dynamically adjusting for light, similar to a video camera, so in reality our human eye has a dynamic range closer to 24 f-stops.

Our human eyes create a mental image of the scene which is a combination of what the eyes see when they are focused on various parts of the scene as depicted above.

Camera film can capture a dynamic range in the order of 14 f-stops. Modern digital camera sensors can usually capture a dynamic range of 5-7 f-stops and some high end DSLR cameras such as the Canon 5D MkIII can capture a dynamic range of about 11.7 f-stops and the Nikon D800 can capture a dynamic range of around 14 f-stops. So there are indeed some limitations with the camera sensor itself in what it can record and capture.

The Solution

So how do we circumvent this problem? One method is to take a range of bracketed photographs of the same scene and blend these into a composite image which captures the best pixels of all the individual images. - somewhat akin to what the human eye is doing. This technique is referred to usually as high dynamic range or HDR photography. Once a set of brackets images have been captured software is required to merge the images together and "choose" the optimum pixels from each bracket - a technique known as tone mapping. By doing this you can extract a lot of additional information from the shadow areas of the image and also minimise any blown out or overexposed portions of the image from the very bright portions of the image, such as the sky.

Using the image at the start of this post as an example let's step through the process I use to capture, edit, post-process the images to maximise the amount of detail and information from the scene.

Image Capture

When taking a series of bracketed photographs for HDR post-processing it is inherently obvious that the camera needs to be in the same position, as does the lens setup and settings. Ideally the camera should be setup on a stable tripod in a position to best capture the scene with the appropriate lens. Depending on the dynamic range of the scene you can take anything from 3 bracketed images, to 5, 7 or even more bracketed images. If the scene has very bright highlights (e.g. bright sunshine) and very dark shadow areas the more brackets should be taken to cover this dynamic range. 

I initially set up the camera on the tripod in the best location and frame the image as required. Then I would set the camera for  the optimum exposure (shutter speed and aperture) and use this as the mid or middle bracket (0EV) I can then use the appropriate number of brackets needed to capture the dynamic range of the scene - you can check the histogram on your camera to make sure you are doing this and covering the complete range of the scene. I maintain the same aperture setting for all the brackets - in this case f/8. For the image in question I took a series of 7 brackets (-3EV, -2EV, -1EV, 0, +1EV, +2EV, +3EV) as shown below.

The 0EV or middle bracket is the usual or normal exposed image you would take if just taking a single image and is shown below.

Although this image is well exposed and actually captures a fair amount of detail both in the bright areas and the shadow areas there is a lot we can do to extract more information and fine detail from this scene.

Image Editing

Once downloaded to the computer we can start the image editing process. I use Aperture as my main photo catalogue system, editor and for basic image post processing. I start by doing some simple editing on the image such as straightening, cropping. You may want to do some other things such as white balance, etc depending on your specific image. I keep the basic edits simple as we may have to do some more once the HDR post processing has been done such as colour adjustments and sharpening which will be done at the very end of the workflow.

HDR Post Processing

For the HDR processing I use Photomatix Pro and I have this installed as a plugin for Aperture which makes it very efficient as the final HDR image is then saved back into the Aperture library, where I like to maintain all my raw and processed images. I have a variety of my own preferred settings for Photomatix but basically what I am trying to do is to create a balanced, well exposed image with maximum information, i.e. retain detail in the highlights and bring out details from the dark shadow areas, without making the image too extreme which many HDR images can tend towards if you are not careful.

The resulting HDR processed image is as below.

Although the image does have more detail in it there are still areas which are a little too dark such as inside the porch area and the doorways to the left and right. I also want to bring out more of the lovely colours and texture in the walls and that front gate so now I will move onto more advanced post-processing to maximise the detail and information from this image.

Advanced Post-Processing - Stylisation

I have been increasingly using the wonderful Perfect Photo Suite from onOne Software and have recently been testing the latest Version 8. Using the Perfect Effects module we can extract more detail from this image and stylise it to the way we want it as detailed below. This module has a extensive library one-click presets, filters and other powerful tools to bring out the most from your image.

The first filter I usually go straight for is the wonderful new Dynamic Contrast which has a number of options, as seen in the left column of the software interface, and these help tremendously to bring out contrast and texture from your image.

You can then sequentially add in filters to work the image to your desired finish point - the stacked filters are listed on the right hand panel so you can adjust each of these individually and the way they are applied to the image. Highly flexible and very easy to adjust and see what you need for your particular image.

I now add in a Bleach ByPass filter at around 50% layer opacity to lighten the image.

I want now to bring out just a little more colour from the walls so I use the Colour Adjustment filter and the Increase Colour option to do this.

I then use the Adjustment Brush (lighten and detail) to bring out information in the dark porch areas, the doorways left and right and of course that wonderful old green gate. This allows you to brush in the adjustments to specific areas of the image and the new Perfect Brush is wonderful at recognising the areas you are working on and not going "outside the lines" as you apply or remove adjustments.

Final Image

All of these changes are subtle and hard to see in a small web image - you really need to see this fullscreen. Of course the post-processing stylisation is really a personal thing and each person will have their own style or requirement for an image. This post briefly outlines the philosophy of the process and describes some of the software tools that allows the user to extract the "data" and then customise it or stylise it to reach the final vision that the user has. I feel the finished image as below and at the top of this post really brings out everything I imagined or saw in the scene and has successfully managed to extract a vast amount of image information or data from the original raw files recorded by the camera.

Authors Note: The author bears no responsibility for anyone calling the iMassage telephone number which is stencilled on the building wall of this image!!

Got Noise?

Even using a high end SLR with a large sensor digital noise can occur at high ISO settings causing pinkish, pixelated speckles which can detract from an image. 

There are a number of sources of noise:

• Heat generated might free electrons from the image sensor itself, thus contaminating the "true" photoelectrons. These "thermal electrons" give rise to a form of noise called thermal noise or dark current.
• Another type of noise is more akin to the 'grain' obtained by using a high ISO film. When we use a higher ISO, we are amplifying the signal we receive from the light photons. Unfortunately, as we amplify the signal, we also amplify the background electrical noise that is present in any electrical system.
• In low light, there is not enough light for a proper exposure and the longer we allow the image sensor to collect the weak signal, the more background electrical noise it also collects. In this case the background electrical noise may be higher than the signal.

So why is using a larger image sensor better? Each photosite on the sensor itself generates electrical noise that can contaminate its neighbor. In a larger image sensor, the photosites can be physically further apart and thus be less affected by that contamination. A larger image sensor also means that the photosite can be larger, thus have a larger light gathering capacity. It is therefore able to generate a larger signal to noise ratio. That is why a digital camera with 6 million pixels crammed into a 1/1.8 in. image sensor has more noise (especially at high ISOs) than a 6MP digital camera using the much larger half-frame (APS-sized) image sensor.

Let's look at an example. The photo below was taken in a very dark internal room of the Preah Khan temple in Siem Reap, Cambodia where I came across a lovely old lady praying. Using only available natural light I shot this image at ISO 3200.

Although the image is still good, especially given the poor lighting conditions, there is visible noise in the image which is more obvious when zoomed in as shown in the image below. You can see the pixelation particularly around the background pink coloured jos sticks just to the left of the lady's face as well as in certain areas of the lady's face.

Noise Ninja is a very effective and productive solution for removing noise and grain from digital photographs and scanned film images. It is a must-have tool for anyone shooting in low-light or fast-action situations -- including news, sports, wedding, and event coverage -- where high ISO photography is required and the resulting noise compromises the image.

Noise Ninja often yields a two-stop improvement in effective image quality, while preserving important image detail. In addition, it can produce cleaner, smoother enlargements from low-ISO images.

Noise Ninja can be used as a plug-in to Aperture or as a standalone application. Using simple slider controls as shown above you can adjust the luminescence strength and the colour (chroma) strength plus carry out sharpening whilst visualising the results of these adjustments on-screen. The picture below shows the original photo above and the noise reduced image below.

The final noise reduced full size image can be seen below.

HDR

What is HDR?

In image processing, computer graphics and photography, high dynamic range (HDR) or high dynamic range imaging (HDRI) is a set of techniques that allows a greater dynamic range of exposures (the range of values between light and dark areas) than normal digital imaging techniques. The intention of HDR is to accurately represent the wide range of intensity levels found in real scenes ranging from direct sunlight to shadows. High Dynamic Range Imaging was originally developed in the 1930s and 1940s by Charles Wyckoff. Wyckoff's detailed pictures of nuclear explosions appeared on the cover of Life magazine in the early 1940s.

Tone Mapping

The process of tone mapping together with bracketed exposures of normal digital images, giving the end result a high, often exaggerated dynamic range, was first reported in 1993, and resulted in a mathematical theory of differently exposed pictures of the same subject matter that was published in 1995. In 1997 this technique of combining several differently exposed images to produce a single HDR image was presented to the computer graphics community by Paul Debevec. This method was developed to produce a high dynamic range image from a set of photographs taken with a range of exposures. With the rising popularity of digital cameras and easy-to-use desktop software, the term "HDR" is now popularly used to refer to this process. This composite technique is different from (and may be of lesser or greater quality than) the production of an image from a single exposure of a sensor that has a native high dynamic range. Tone mapping is also used to display HDR images on devices with a low native dynamic range, such as a computer screen.

Bracketing

The technique of taking HDR photos means taking bracketed shots at different exposures; one at the correct exposure and others which are underexposed and overexposed to create a number of images covering a range of exposures, e.g. -2EV, -1EV, 0EV, +1EV and +2EV. This technique is particularly useful when taking a high contrast scene - I’m sure we have all experienced those difficult shots with deep shadows and bright sky where you either have no detail in the shadows or blow out the sky completely.

Single RAW HDR

However rather than taking a number of bracketed shots when shooting in RAW format you have the opportunity to make a pseudo HDR image from just one image. As a RAW image has a higher dynamic range compared to a normal jpeg image you can produce a number of jpgs or tiffs from one RAW image at different exposures. You can produce 3 images at -2EV, 0EV, and +2EV or if you use 5 images, -3EV, -1.5EV, 0EV, +1.5EV and +3.0EV then use these images at different exposures to create a pseudo HDR image.

There are a number of HDR processing applications but I use Photomatix which has a number of tools to assist you in this process.

Example

Now let's take this image of Ta Phrom temple in Siem Reap, Cambodia and see how we can do a pseudo HDR technique. Here is the photo taken at 0EV exposure and as you can see we have some very dark shadow areas and a very bright sky overhead resulting in an average exposure which does not bring out any detail in these two areas.

So taking the original RAW image in Aperture we can adjust the exposure setting to a number of settings such as here, -3EV, -1.5EV, +1.5EV and +3EV to produce four more jpg images.

-3EV

-1.5EV

+1.5EV

+3EV

We then import all the five jpg images into Photomatix where we can run through a tone mapping process which blends these 5 images into a single image. Here is the final HDR image which you can see clearly has well defined exposure of the sky and the dark shadow areas.

Black & White

Even in the modern digital age black & photography still has a magical appeal to many people and can dramatically change the drama and impact of a photograph. Many of the modern digital SLR cameras have pre-set settings to generate black & white or sepia toned pictures to offer this capability but a far better way to do this is to do this in the post-processing phase.

I always take RAW format photos which allows me the ability to do some post-processing adjustments where needed such as exposure, white balance, etc. Although these RAW images are full colour, using a powerful black & white post processing software such as Silver Efex Pro from Nik Software, I can generate a large variety of black & white image effects.

Silver Efex Pro offers the power to control professional quality black & white images with patented U-Point technology to selectively control tonality and contrast in the image, a state-of-the-art grain engine to recreate traditional style black & white images, emulation of many popular film types and stylizing of images with popular tints and toners.

Let's look at how we do the black & white processing .... here is an original colour image of the famous Taj Mahal at Agra in India.

Silver Efex Pro is a plug-in to Aperture so we simply select Images, Edit With, Silver Efex Pro to bring up the application.

The default view is as below with a neutral black & white effect.

Or we can split the screen with the original colour and black & white effect.

We can then choose a number of pre-set effects from the left hand column, such as the High Structure effect as shown here.

Here are another two examples:

Dark Sepia

Antique Plate

Alternatively we can change the individual settings for brightness, contrast, structure, colour filters, film types or stylizing. We can adjust grain to reproduce an "antique" film effect. We can also add in control points to adjust brightness, contrast and structure in specific areas of the image which can be useful for example to reduce blown-out areas as shown in the example below where the top right of the Taj Mahal dome is over exposed. Each control point has individual sliders for brightness, contrast and structure as well as the area of influence.

The finished image produces a dramatic black & white effect as seen below.

Panoramic Photography

Panoramic photography has always been one of my interests and usually there are numerous opportunities to use this technique to highlight a dramatic view or landscape which normally cannot be captured within the limitations of a one frame shot. During a recent visit to Paris I took an early evening walk by the famous Louvre Museum which was beautifully lit up illuminating the wonderful contrast of the famous glass pyramid with the backdrop of the older architecture of the museum buildings; an ideal candidate for a panorama.

I shot 8 individual frames covering the extent of the buildings using an approximate 25% overlap between frames using an ISO of 800.

After running through my basic workflow in Aperture I exported the 8 frames as full resolution jpeg files and then imported these into Kekus Digital's Calico 1.4rev2 application where the frames where interpolated, blended and then merged into a horizontal panorama as shown below.

Here is another typical landscape which can be an ideal opportunity to create a dramatic panorama. These 5 shots were taken at Suances on the northern Atlantic coast of Spain all taken at ISO100.

Again after post-processing through Aperture the 5 frames were exported as jpegs, imported into Kekus Digital's Calico 1.4rev2 application where the frames where interpolated, blended and then merged into a horizontal panorama.

Calico software is an automatic multi-row photo stitcher application. Calico was developed with ease of use in mind and unlike many other stitching programs, does not limit you to a single row of images or a 3x3 mosaic. With Calico, you can shoot several rows of images or a single row.

Photo Tip - Motion Effect

On a recent holiday in Spain I came across a lovely old merry-go-round at the beachfront in San Sebastian which was a great subject for a photo. Thinking a little creatively I wanted to capture the sense of motion so dialed in a slow shutter speed to my camera. Problem ..... this was mid-day and extremely bright so even at the smallest f22 aperture the shot was completely blown out and overexposed. I abandoned these shots and assumed them to be in the reject category - luckily I never usually delete any shots on the camera.
I forgot about the merry-go-round shots I had taken until later when post-processing my holiday photos I came across the completely blown-out merry-go-round shot as shown here.

Going through my normal Aperture workflow, and out of curiosity, I grabbed the exposure slider and pulled this back dialing in a -2.00 EV value and miraculously managed to pull out a reasonable picture highlighting the merry-go-round movement as I had wanted.

This shows the advantages of using RAW format when taking photos allowing you the ability to adjust key parameters such as exposure in the post-processing phase.