the histogram exposed (vi) – multipeak

This series of photographs and their associated histograms covers images with multipeak histograms, which come is many differing forms. None of these images is perfect, but they illustrate the fact that sometimes the perfect image is not possible given the constraints of the scene – shadows, bright skies and haze, sometimes they are just unavoidable.

Histogram 1: A church and hazy hills

This photograph is taken in Locarno, Switzerland, with the church in the foreground the Madonna del Sasso. The histogram is of the multipeak variety, with few highlights. The left-most hump (①) represents the majority of the darker colours in the foreground, e.g. vegetation, and the parts of the building in shadow. The remaining two peaks are in the midtones, and represent various portions of the sky (③) as well as the lake, and hazed over mountains in the distance (②). Finally a small amount of highlights (④) represent the clouds and brightly lit portions of the church.

Fujifilm X10 (12MP): 7.1mm; f/5; 1/850

Histogram 2: Light hillside, dark forest

This is the Norwegian countryside, taken from the Bergen Line train. It is a well contrasted image, with only one core patch of shadow (①), behind the trees in the bottom left (there are a few other shadows in foreground objects such as the trees on the right). The midtones, ②, represent the rest of the landscape, with the lightest midtones and highlights composing the sky, ③.

Olympus E-M5II (12MP): 12mm; f/5; 1/400

Histogram 3: Gray station

This photograph is of the train station in Voss, Norway. It is an image with a good distribution of intensities, with four dominant peaks. The first peak, ①, is representative of the dark vegetation, and metal railings in the scene, overlapping somewhat into the mid-tones. The central peak (②) which is in the midtones, represents the light green pastures, and the large segments of asphalt on the station platform. The third peak, ③, which transitions into the highlights mostly deals with the light concreted areas. Finally there is a fourth peak, ④, which is really just a clipping artifact related to the small region of white sky.

Olympus E-M5II (12MP): 40mm; f/5; 1/320

the histogram exposed (v) – indistinct

This series of photographs and their associated histograms covers indistinctly shaped histograms, i.e. images which have a histogram which does not really have any distinct shape.

Histogram 1: Dark depths

This is a good example of a low-key image, but contains content which makes this an aesthetically pleasing image. The histogram shows as asymmetric unimodal, tiered towards the darker tones. The dark tones, ①, are naturally provided by the black hull of the ship, the dark vegetation, and the water. The midtones, ②, are associated with the lighter vegetation, and the ships reflection in the water. The larger of the two peaks in the highlights, ③, is the side of the ship, and the building on-shore, and the smaller one, ④, basically is the white on the front of the ship.

Olympus E-M5II (12MP): 20mm; f/4; 1/160

Histogram 2: Light buildings

This is an excellent example of an image (Bergen, Norway) which has white clipping, but it doesn’t have much to do with blown-out regions. The whites in the image are entirely associated with the sides of the two larger buildings which are exposed to direct sunlight. This is not a distinct multipeak histogram, but it is divided into four tonal zones: ① the shadows; ② the midtones; ③ the upper midtones and highlights; and ④ the whites.The sun was intense on this day leading to a slightly paler sky, and bleached buildings facing into the sun.

Olympus E-M5II (12MP): 17mm; f/5.6; 1/250

Histogram 3: Red train

This image of a train at the station in Voss (Norway) which has a histogram which covers a broad range of tones. The image has good contrast overall with only two distinct peaks: ① Values 87-124 comprise most of the red and dark gray portions of the train, as well as fine detail throughout the image; and ② Values 234-245 comprises the edge of the train roof. Images which contain a lot of detail and varied tones typically produce histograms containing a lot of “spiky” detail.

Olympus E-M5II (12MP): 19mm; f/4.5; 1/200

the histogram exposed (iv) – multipeak-unimodal

This series of photographs and their associated histograms covers multipeak-unimodal histograms, i.e. images which have a histogram which has a core unimodal shape, yet is festooned with peaks.

Histogram 1: A statue against the sky

This image, taken near Glasgow Scotland, has a broad spectrum of intensity values. The histogram has an underlying core “unimodal” shape, bias towards highlights, a result of both the statue and the clouds. The image has exceptionally good contrast. The jagged, multipeak appearance is an artifact of the broad distribution of intensities, and intricate details, i.e. non-uniform regions, in the image.

iPhone 6s (12MP): 4.15mm; f/2; 1/3077

Histogram 2: Oslo lion

This image, taken in Oslo (Norway), is the “poster-boy” for good histograms (well almost). It has an underlying unimodal shape, mostly in the midtones. It is a well-formed image with good contrast and colour. There are shadows in the image, but that is to be expected considering the clear sky and the orientation of the sun. There are no pure blacks in the image, the shadow tones created by the dark windows. There are also few whites, less than 1% of pixels, that are the result of light reflecting off light surfaces (such as the lion).

iPhone 6s (12MP): 4.15mm; f/2; 1/1012

Histogram 3: Plateau river

This image, taken from a moving train on the Bergen Line in Norway, high up on a mountain plateau. The histogram has an underlying core unimodal shape, composed predominantly of midtones, in addition to the lighter end of the shadows (①). There are no blacks and few highlights to speak off. The image has exceptionally good contrast. The jagged, multipeak appearance is an artifact of the image detail, i.e. non-uniform regions, in the image. For instance the sky tapers gradually from 150 to 190 near the top of the hill.

Olympus E-M5(II) (12MP): 12mm; f/7.1; 1/400

the histogram exposed (iii) – bimodal

This series of photographs and their associated histograms covers aesthetically pleasing bimodal histograms.

Histogram 1: A sky with texture

This image (of a building in Edinburgh) has a broad spectrum of intensity values. The histogram is bi-modal with two distinct humps. The right peak is associated with the overcast sky (and white van). The left shallow mound comprising both midtones and shadows makes up most of the remaining image content. There is a small flat region in between the two that makes up features like the lighter portions of the building. Note that pixels maps on the right of the histogram below show the associated pixels in black.

Histogram 2: Out on the lake

This photograph of the Kapellbrücke was taken in Lucerne, Switzerland. The histogram is bimodal, and asymmetric, and reflects the information in the image: the left hump (①) is associated with the lower portion of the image (shadows and midtones), and the right peak (② highlights) with the sky. There is relatively well contrasted image. The clouds have some good variation in colour, as opposed to begin pushed completely into the whites.

Fujifilm X10 (12MP): 7.1mm; f/9; 1/800

Histogram 3: Carved in stone

This is a photograph of the Lion of Lucerne, in Lucerne, Switzerland. It provides a classic asymmetric bimodal shaped histogram. The left mound, ①, contributes the images dark, shadowy regions, whereas the remaining, larger peak ②, bias towards highlights, defines most of the remaining image. It is well contrasted given that a shadow is cast on the sculpture as it is relief into the wall. The overlapping region between the two entities, ③, forms the transition regions from ① to ②, often visualized in the picture as regions of low “shadow”.

Fujifilm X10 (12MP): 21mm; f/3.2; 1/850

the histogram exposed (ii) – highlight-clipping

This series of photographs and their associated histograms covers good renditions of highlight clipping, i.e. photographs in which there are regions of white pixels, but they either genuinely exist in the image as white regions, or do not directly impact the aesthetics of the image.

Histogram 1: A bright overcast sky

The image was taken on a very overcast day in Montreal. This is a good example of an image with highlight-clipping in the histogram, which is neither good nor bad. The building itself does not suffer from a lack of contrast, although the non-sky region can be enhanced slightly with no ill effects on the sky (because it is already basically white). This is a common situation in outdoor, overcast scenes. In an ideal world, more texture and contrast in the sky would be great, but in reality you have to use what nature provides.

Histogram 2: White buildings

This photograph was taken in Luzern, Switzerland. It is a well contrasted image, with a somewhat indistinct, multipeak histogram. The pixels are well distributed over the range of intensities, except for the spike at values 240-255. Here highlight clipping seems as though it has occurred because there are quite a number of white pixels in the image. However this density of white pixels comes not from anything being overblown, but rather from the white buildings in the image (of which there are many).

Fujifilm X10 (12MP): 7.1mm; f/4.5; 1/950

Histogram 3: A bit of overblown sky

This photograph was taken in Grabs, Switzerland. The histogram is a nonuniform, and basically unimodal in shape, with the exception of a huge spike in the whites causing clipping. But this is a case of the highlight clipping not really affecting the core content of the image, i.e. it comprises the overblown sky in the top-left of the image. On a bright, partially overcast day, this is not an unusual scenario.

Fujifilm X10 (12MP): 7.1mm; f/2; 1/900

the histogram exposed (i) – unimodal

This is the first post in an ongoing series that looks at the intensity histograms of various images, and what they help tell us about the image. The idea behind it is to try and dispel the myths behind the “ideal” histogram phenomena, as well as helping to learn to read a histogram. The hope is to provide a series of posts (each containing three images and their histograms) based on histogram concepts such as shape, of clipping etc. Histograms are interpreted in tandem with the image.

Histogram 1: Ideal with a hint of clipping

The first image is the poster-boy for “ideal” histograms (almost). A simple image of a track through a forest in Scotland, it has a beautiful bell-shaped (unimodal) curve, almost entiorely in the midtones. A small amount of pixels, less than 1%, form a highlight clipping issue in the histogram, a result of the blown-out, overcast sky. Otherwise it is a well-formed image with good contrast and colour.

Histogram 2: The witches hat

This is a picture taken along the route of the Bergen-Line train in Norway. A symmetric, unimodal histogram, taking on a classic “witches hat” shape. The tail curving towards 0 (①) deals with the darker components of the upper rock-face, and the house. The tail curving towards 255 (③) deals with the lighter components of the lower rock face, and the house. The majority of midtone pixels form the sky, grassland, and rock face.

Olympus E-M5MArkII (16MP): 12mm; f/6.3; 1/400

Histogram 3: An odd peak

This is a photograph of the statue of Leif Eriksson which is in front of Reykjavik’s Hallgrímskirkja. It provides for a truly odd histogram – basically the (majority of) pixels form a unimodal histogram, ③ , which represents the sky surrounding the statue. The tiny hillocks to either side (①,②) form the sculpture itself – the left forming the shadows, and the right forming the bright regions. However overall, this is a well formed image, even though it may appear as if the sculpture is low contrast.

Leica D-Lux 6 (10MP): 14.7mm; f/2.8; 1/1600