{"id":1573,"date":"2010-12-26T07:49:00","date_gmt":"2010-12-26T15:49:00","guid":{"rendered":"http:\/\/ralphnordstromphotography.com\/wordpress\/articles\/mastering-exposurehistograms-part-2\/"},"modified":"2019-11-18T21:02:00","modified_gmt":"2019-11-19T05:02:00","slug":"mastering-exposurehistograms-part-2","status":"publish","type":"post","link":"https:\/\/ralphnordstromphotography.com\/wordpress\/2010\/12\/26\/mastering-exposurehistograms-part-2\/","title":{"rendered":"Mastering Exposure–Histograms Part 2"},"content":{"rendered":"

A few weeks ago I published the first of a series of articles on histograms, \u201cMastering Exposure \u2013 Histograms Part 1.<\/a>\u201d\u00a0 I eventually want to talk about different types of histograms and how to work with them in the field and during the post processing.\u00a0 But before getting into that I want to take a deeper dive into the histogram itself.<\/p>\n

<\/p>\n

In the first article I defined a histogram as a graph that shows the relative amounts of each shade of gray in the scene we are photographing from pure black to pure white.\u00a0 I need to modify that definition just a bit because we don\u2019t see the world in shades of gray but rather in color.\u00a0 The definition should be, \u201cA histogram is a graph that shows the relative amounts of each tonality in the scene we are photographing from pure black to pure white.\u201d\u00a0 Tonality is lightness and darkness and is one of the three physical properties of light \u2013 tonality (or\u00a0 luminance), hue (or color) and saturation (or purity of color).<\/p>\n

Dynamic Range of the Scene<\/h3>\n

To really understand histograms we need to understand dynamic range.\u00a0 Dynamic range is the difference between the darkest and brightest parts of a scene.\u00a0 The difference is measured in stops.\u00a0 In an outdoor scene on a bright sunny day the dynamic range might be seven, eight or more stops.\u00a0 On an overcast day the dynamic range might be only three or four stops (at least as long as we keep the sky out of the composition).\u00a0 Some situations have very narrow dynamic ranges like during twilight or in open shade.\u00a0 In some extreme situations dynamic ranges can be ten, twelve or even more stops.\u00a0 I’m thinking of photographing slot canyons such as Antelope Canyon.<\/p>\n

Every scene we photograph has a dynamic range whether photographing in a studio or outdoors.\u00a0 In the studio we have control over the dynamic range because we controlled the light.\u00a0 But outdoors we have no control.<\/p>\n

Dynamic Range of the Sensor<\/h3>\n

Our camera\u2019s sensor also has a dynamic range.\u00a0 But with the sensor, the dynamic range is fixed.\u00a0 Digital cameras typically have dynamic ranges of six or seven stops.\u00a0 Some high end digital cameras have dynamic ranges of eight, nine, ten or more stops.\u00a0 But if you have a digital camera with a moderate dynamic range, the only way you can increase it is to upgrade to a more expensive model.<\/p>\n

The histogram on your camera shows the dynamic range of the sensor.\u00a0 The left side of the histogram is the maximum darkness the sensor can capture and right side is the maximum brightness.\u00a0 Said another way, the left side is pure black and the right side is pure white.<\/p>\n

It\u2019s important to understand that the notion of \u201cblack\u201d and \u201cwhite\u201d is from the sensor\u2019s point of view, not the scene you\u2019re photographing.\u00a0 The scene never really has a pure black in it because pure black would be the total absence of light and even the darkest shadow has some light in it.\u00a0 One might argue that a fluffy white cumulus cloud on a bright sunny day might be pure white but specular highlights off of chrome or water are even brighter and the sun itself is brighter still.\u00a0 So the idea of pure black and pure white is really related to the end result, the photograph, and the sensor (or frame of film) from which it is produced and not the scene.<\/p>\n

Mapping the Two Dynamic Ranges<\/h3>\n

The graph of the histogram shows how the dynamic range of the scene you are photographing maps to the dynamic range of the sensor.\u00a0 Because the dynamic range of the scene can vary but that of your camera cannot, it\u2019s unlikely that the two will always match up.\u00a0 If the scene you are shooting has a dynamic range that is less than or the same as your sensor\u2019s then everything works out fine.\u00a0 But if the scene\u2019s dynamic range is greater then that of the sensor, then the graph will completely fill the histogram and begin to climb both sides.\u00a0 This is when you start running into shadow clipping, highlight clipping or both.<\/p>\n

Here\u2019s an example of just such a scene photographed on a very bright day.\u00a0 It was shot in the town of Colmar in the Alsace region of France.<\/p>\n

\"_A1P6493_scene_dynamic_range\"<\/a><\/p>\n

The dynamic range was a little beyond what the camera\u2019s sensor could capture as you can see in the figure below.\u00a0 The top graph represents the actual dynamic range of the scene and the bottom, the dynamic range as captured by the camera.<\/p>\n

\"high_dynamic_range_histograms\"<\/a><\/p>\n

The scene\u2019s dynamic range exceeds that of the sensor.\u00a0 Therefore the scene\u2019s dynamic range must be compressed to fit into the sensor\u2019s smaller dynamic range.\u00a0 As a result the right end of the scene\u2019s histogram is smashed up against the right wall.\u00a0 The results are dramatic; the graph climbs the wall very sharply.\u00a0 A similar thing is happening at the shadow end of the graph.\u00a0 And while the results weren\u2019t quite as dramatic the graph is still shoved up against the left wall.<\/p>\n

As shot, this image has both shadow and highlight clipping.\u00a0 If the camera is set up to save the image as a JPEG then you\u2019re going to get clipping in the image and there\u2019s not much that can be done with it.\u00a0 However, if the image is stored as a RAW file then there\u2019s a chance the highlights and shadows can be recovered.\u00a0 Here\u2019s an example of what can be done with a RAW file.<\/p>\n

\"_A1P6493_recovered\"<\/a><\/p>\n

If the dynamic range of the scene is less than the sensor\u2019s, the graph will fit well within the histogram.\u00a0 That is assuming the image is not over or under expose in which case the graph will be skewed to one side or the other.<\/p>\n

An example of this is a photograph I shot of the Munster Cathedral in Basel, Switzerland.<\/p>\n

\"_A1P6429_scene_and_sensor_dynamic_range\"<\/a><\/p>\n

This is clearly a very low contrast scene and the histograms of the scene and the camera\u2019s sensor are virtually identical.<\/p>\n

\"low_dynamic_range_histograms\"<\/a><\/p>\n

The sensor has no problem capturing the full dynamic range.<\/p>\n

By the way, here\u2019s an example of what can be done with an image like this.<\/p>\n

\"_A1P6429_recovered\"<\/a><\/p>\n

Two Critical Pieces of Information<\/h3>\n

So the histogram provides us with two critical pieces of information.\u00a0 First it tells is how the dynamic range of the scene maps to the dynamic range of the sensor.\u00a0 The width of the graph shows the dynamic range of the scene.\u00a0 If the graph extends from one side to the other without touching the sides then the dynamic ranges of the scene and the sensor are very much the same .\u00a0 If the graph is touching both sides then the dynamic range of the scene exceeds that of the sensor.<\/p>\n

Second it tells us whether our image is over, under or correctly exposed.\u00a0 The position of the graph shows the exposure.\u00a0 In the graph is shifted to the right the image is probably over exposed.\u00a0 And if it\u2019s up against the right side but not touching the left, then the image is definitely overexposed and you have highlight clipping.\u00a0 If the graph is shifted to the left you have the opposite situation and your image is probably under exposed.<\/p>\n

So the histogram is a very important tool that digital photographers can use to help us establish that all-important foundation for a great photograph, the correct exposure.<\/p>\n

Join me on an upcoming workshop.\u00a0 Click here for more details.<\/a><\/p>\n

To see more of my photographs click here.http:\/\/ralphnordstromphotography.com\/workshops\/<\/a><\/p>\n

(2902)<\/p>\n","protected":false},"excerpt":{"rendered":"

Take a deep dive into the often misunderstood histogram and discover the critical role it plays in capturing great photographs.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[3,281,296,4],"tags":[297,266,279,199],"class_list":["post-1573","post","type-post","status-publish","format-standard","hentry","category-articles","category-expoure","category-histogram-how-to-articles","category-how-to-articles","tag-dynamic-range","tag-exposure","tag-histogram","tag-photography-workshops"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p9Nl7-pn","jetpack_likes_enabled":true,"_links":{"self":[{"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/posts\/1573","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/comments?post=1573"}],"version-history":[{"count":5,"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/posts\/1573\/revisions"}],"predecessor-version":[{"id":4613,"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/posts\/1573\/revisions\/4613"}],"wp:attachment":[{"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/media?parent=1573"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/categories?post=1573"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ralphnordstromphotography.com\/wordpress\/wp-json\/wp\/v2\/tags?post=1573"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}