Advanced Tutorial 8
The option to display a Histogram graphic on-screen when shooting, or reviewing shots, may seem like a step too far into the technicalities of photography. But don’t be put off! This is a useful tool that, with practice, can greatly aid you in achieving better exposures – here’s how…
Understanding & using the Histogram
The ‘Histogram’ display gives photographers access to a powerful tool for achieving good exposures. An understanding of it will help you take images revealing the maximum detail under difficult conditions.
But given that the display screen shows immediately whether a shot is too dark or too light, allowing you to adjust exposure accordingly, what additionally can the Histogram offer?
What is a Histogram?
Familiar in mathematics, Histograms are graphical displays of data using bars of different heights. Similar to a bar chart, it groups related values into ranges shown as the vertical bars. The Histogram does not replace the need to review images on-screen, but does offer extra information not immediately obvious to your eye.
Its graphical representation of the entire luminosity range highlights exposure problems that are otherwise invisible when viewing on the LCD screen alone.
The brightness of every pixel within a scene is displayed, the output of each grouped with others of the same value, forming the ‘mountain range’ graph.
Your camera’s preview display can lack the absolute precision to see if an image is failing to capture information that may otherwise be visible. The Histogram, viewed on the LCD screen as shown, reveals those points under all conditions.
Put simply, try to avoid exposures with Histograms showing a high bias to the left or right. The left side reveals lowlights or shadowed parts of a scene; pixels this end of the scale will record a very dark grey, even black– leading to potential loss of detail there.
Right-edge pixels will record as white, again potentially losing detail (‘blown out’ highlights). Loss of detail at either end is known as ‘clipping’. Pixels recorded in the central section are ‘mid-tone’, potentially holding the maximum detail.
Reading from left to right, the x-axis shows 256 levels – ‘8-bit greyscale’ (as it is termed, in reference to binary code) from ‘zero’, black, to ‘255’, white. The y-axis shows the number of pixels registering each such value. If you took a 12MP image with your lens cap on, its Histogram would be a single column at zero on the x-axis and 12,000,000 on the y.
Interpreting the display
It is not the actual numbers that are important, though; it is the shape of the curve that is your guide to correction.
Take, for example, this flower image on the right, the Histogram clearly extends off the right-hand edge, demonstrating that many pixels are registering extremely bright – detail in the bright areas (the sky) will be lost due to clipping.
The owl image (shown in the display above) contains fairly even numbers of pixels across the whole range with drop-off at either end – the sought after ‘bell-shaped’ curve. The wide range of dark to light areas demonstrates a good exposure with high contrast.
This tool provides guidance only – you will encounter scenes with such a wide exposure range that you cannot capture both the shadow detail and the brightest highlights. So, it is not always possible to set an exposure for the perfect ‘bell-shaped’ Histogram curve.
Also, you may choose to deliberately overexpose, to blow the highlights. Or, you might underexpose to produce a silhouette. Using the Histogram enables you to judge accurately how much effect adjustments will have.
Expose to the right
Although this beach shot appears pretty bright, the Histogram shows how all the highlight details have been captured –a typical result that is a product of ‘Exposing to the right’ – what we call getting the best tonal range in the conditions.
The display shows most of the exposure is towards the right-hand end of the scale, but very little if any actually reaches the edge – meaning all the bright highlights and detail were recorded:
For those looking to further enhance their images with editing software later, it is often easier to brighten a slightly dull image, rather than recover detail from much overexposed highlights. And for those seeking maximum control, shooting in RAW will yield files that developer software can adjust with considerable finesse. As we discovered in the previous tutorial, using RAW files takes advantage of the full dynamic range capabilities of the camera, rather than just the 8-bit used for JPEGs.
Using your camera’s Histogram in real-time
To avoid the need for too much subsequent work, shoot in ‘Live View’ mode and display the ‘real-time’ Histogram while you shoot. Exposure adjustments will be immediately reflected in its display, allowing you to fine-tune as you go.
A number of factors may influence your exposure, so remember these points when you are out in the field:
- Pure black and bright white will show as clipped – if the Histogram curve reaches either side, they won’t be recorded accurately.
- Reflections of highly polished or mirror-like subjects will always blow out.
- A pure white background should look overexposed, otherwise it will show as dirty grey on your final image.
- An evenly lit scene that is well exposed will show the majority of the ‘peaks’ in the ‘mid- tone’ area – resulting in that sought-after ‘bell-shaped’ curve.
Because Histograms are imperfect and based on a JPEG preview of the scene, familiarity with your camera and its reactions to given conditions will also be your guide. The display is relatively small and actually biased towards representing brighter tones (roughly half relates to the upper 20% of the exposure range), so interpreting the shape and how it relates to the final result takes practice.
These examples may help give an insight to get you started:
1. High contrast
This scene has a larger tonal range than the camera can easily cope with. The exposure for the crashing water is very different to that required by the dark rocks. Try adjusting exposure to capture more of the highlight detail and perhaps accept the loss of detail in the rocks.
2. Low contrast
With a subject with a limited tonal and contrast range, you may well appear to get a very bell-shaped Histogram. Unfortunately, this picture lacks dynamism! Adjusting the exposure to the right should yield a more vibrant image.
3. Bright/dark backgrounds
Bright backgrounds will naturally produce a heavily right-biased curve. In a studio setting with a plain white backdrop, this is perfectly acceptable. So in this picture, strong clipping shows on the right of the Histogram. The reverse is true shooting against black – remember, if you want the blackest of blacks, some clipping at the left edge will likely be required.
These are simple examples of the information that the histogram provides, understanding it will inform the choices when controlling your exposures, although it may take time and practice. Remember there is no such thing as the perfect exposure – just the best you can make to achieve the result you are aiming for.
The LUMIX Advantage
LUMIX G cameras offer the flexibility to position the Histogram on-screen at any point of your choosing, right to the edge of the frame, which allows for precise compositions and important details don’t get obscured.
With touch-screen models such as the G6, you can even drag the Histogram around with your finger.
Now, find an interesting composition with a wide range of brightness levels and shoot according to your camera’s automatic metering. Next, shoot it applying your own exposure compensation after examining the reviewed image. Lastly, using the live-view Histogram, adjusting based on the parameters covered in this tutorial.
Review the three results by comparing the amount of detail in each!
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