Is it a photo that looks clear and bright?
Is it a photo that looks sharp and detailed?
Is it a photo that contains no digital noise and digital artefacts?
Is it a photo that reproduces colour very accurately?
The truth is that it’s a combination of these and other factors that will contribute to what we finally determine good image quality. Only when we become more experienced and our technical ability improves will we come to understand the differences in image quality.
I aim demonstrate how you can improve the image quality of your photos by increasing its dynamic range with the use of practical examples and processing tips. This is not intended to be very technical and it’s not a lesson in Photoshop but just a way to help you to understand and utilise the potential of your camera in order to improve image quality.
Image Quality and Dynamic Range
One of the ingredients that contribute to good image quality that many enthusiast photographers regard as important is a camera’s ‘dynamic range’.
The dynamic range of your camera describes the ratio between the maximum and minimum measurable light intensities from white to black that your camera can record, or in other words from the brightest highlight to the darkest shadow.
The dynamic range capability of a camera will determine how much detail and colour information is discernible from the brightest highlights to the darkest shadows of a photo. What the camera reproduces aims to be close to what we saw in the original scene so it's best to shoot a RAW file to ensure you make the most of the dynamic range on offer
When a scene exceeds the dynamic range of a camera it results in the highlights being washed out and the shadows being reduced to black (highlight and shadow clipping), hence little detail can be seen these areas of the photo.
If your photography is more about artistic interpretation and/or special effects rather than faithful reproduction then this may not be of much concern to you. However, knowing how to produce good image quality in the first instance means you can deviate from it successfully to meet your artistic endeavours. If you know the rules then you know how to break them. This will enable you to be adaptable and broaden the scope of your photography.
High Contrast Scenes
High contrast scenes that contain very bright and very dark areas are the most problematic when trying to produce a good exposure and will push the limits of your cameras dynamic range. Conversely, a low contrast scene contains less levels of tone and falls within the boundaries of your cameras dynamic range, producing images that look very natural. See image 1 and 2.
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| Image 1 - high contrast (out of camera JPEG) |
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| Image 2 - low contrast |
Optimum ISO
The base ISO (minimum ISO) setting of your camera is often the optimum ISO setting. Optimum meaning this ISO offers the widest dynamic range so can record more information in the highlight and shadow areas of an image. It is also the ISO setting that will produce the least digital noise. As ISO sensitivity is increased the dynamic range of your camera is reduced. Some cameras offer ISO 100 as the base ISO but others may only offer it as an ISO extension, which means it is not the optimum ISO setting and therefore does not offer the widest dynamic range. It is useful to know the optimum ISO setting of your camera if you want to make good use of its dynamic range. On Olympus or Panasonic cameras it’s usually ISO 200.
Increasing Dynamic Range in Practice
Increasing the dynamic range of your photo effectively means optimising the exposure to include a wider range of tones, giving a smoother transition from highlights to shadows. Flash lighting is one way to increase the dynamic range of a photo by filling in the shadow areas with extra light while the camera exposes for the highlights. I won’t go into using flash but will concentrate on post processing as a way of increasing dynamic range.
Adobe Photoshop Elements 11 has been used for this example. The RAW file is opened in Photoshop activating the Adobe Camera Raw (ACR) workspace.
Image 3 shows the high contrast RAW photo opened in the ACR workspace with no adjustments made. As you can see the hard sunlight has blown the highlights and although not much clipping has occurred in the shadow areas, they still are too dark. To make things more difficult it was shot at ISO 400, which is not the optimum ISO.
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| Image 3 - ACR workspace |
Note the shape of the histogram at the top right hand corner of the screen showing the brightness levels of the photo. The left side of the histogram indicates shadows, the right side highlights and the centre mid-tones. In the histogram when the graph is skewed to the extreme left or right it means there is highlight and/or shadow clipping occurring (over and/or under-exposure).
On the histogram there are two boxes containing a triangle. The highlight clipping box (top right), indicates clipping in the viewing area with a red warning. Click this box to activate warning. Move highlights or whites slider to adjust. When the box turns black it means there's no clipping occurring.
The shadow clipping box (top left) indicates shadow clipping in the viewing area with a blue warning. Move blacks or shadows slider to adjust. The exposure slider can also be used for adjustment.
Image 4 shows the highlight and shadow clipping warnings activated to guide your adjustments.
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| Image 4 - clipping warnings activated |
Image 5 shows the adjustments made to recover the exposure in order to reproduce the scene closer to what I saw in reality. The highlights and shadows sliders are the important tools here as that's where the main adjustments need to be carried out. Study the adjustments palette to see the sliders final adjustment values.
If you observe the histogram you'll see that the mid-tones have been lifted and the red highlight warning on the image has almost disappeared. I've also used cloudy white balance to give a warm tone to the photo, which is simply a short cut instead of using custom white balance to adjust the colour temperature.
This is intentionally an extreme example to challenge the dynamic range of the camera so you can see the difference. There comes a point when the full dynamic range of the camera has been utilised and no further correction can be made. At this point you can only aim to balance the exposure.
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| Image 5 - final adjustments |
Now lets look at images 6 and 7 paying particular attention to the goods for sale and the foliage. Image 6 is the original JPEG and image 7 is the RAW corrected image. Open them in separate tabs and toggle between the two to see the difference. It is now much easier to decipher what the goods for sale are as they now appear more clearly - the foliage is also much clearer.
I'm not saying the photo is now perfect bearing in mind that it was taken in hard sunlight at a less than ideal ISO 400, but the dynamic range of the image has been successfully increased. There is now more detail present in the highlights and the shadows and it's technically an improvement on the original.
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| Image 6 - original JPEG |
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| Image 7 - corrected |
Image 8 has been added to be compared to image 6 and 7. I've tweaked the adjustments that were made on image 7 slightly brightening the highlights and lowering the contrast of the image. It's subtle but the difference can be seen. You can make as many adjustments to the raw file as you want until you get a look that you find acceptable.
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| Image 8 - tweaked |
The final look of the photo is really down to the photographer. If I'm trying to increase the dynamic range then it means I'm usually trying to achieve a realistic looking image rather than a stylistic one. In this circumstance exposure accuracy will be given more importance. If my post processing is for creative purposes then the rule book gets thrown out of the window! The important thing is that you know how to correct a photo should you need to.
Practice this with your own photos and make a point of shooting some high contrast scenes to work on.
Important processing tips
a) When brightening shadows digital noise is introduced. Noise reduction will have to be applied if the effect of noise is not to your taste. I did not apply any noise reduction to the final image because the noise that was introduced took on a film appearance that I find appealing.
b) Increasing the dynamic range (highlights and shadows correction) in processing can have a negative affect on the contrast and render the image looking unnatural. The clarity slider will help to balance this by adjusting the local contrast (targeted areas of low contrast) where necessary.
c) Colour accuracy will be affected when brightening shadows and darkening highlights. Use the Vibrance and Saturation sliders to improve colour accuracy. Use +Vibrance along with -Saturation to get a realistic looking image.
Definitions
1) Dynamic Range - the ratio between the maximum and minimum measurable light intensities from white to black (highlights to shadows).
2) Clipping - loss of detail or information in an image.
3) Highlight Clipping - areas of the image that are over-exposed. Loss of detail in the highlights.
4) Shadow Clipping - areas of the image that are under-exposed. Loss of detail in the shadows.
Finally
Don’t become obsessed with the concept of image quality; it’s not the be all and end all of photography. It’s better to take lots of photos and improve gradually until both the technical and artistic sides unite and you begin to create better images.