{"id":17721,"date":"2011-08-19T11:07:54","date_gmt":"2011-08-19T11:07:54","guid":{"rendered":"http:\/\/www.labri.fr\/perso\/barla\/blog\/?p=17721"},"modified":"2012-07-09T16:04:06","modified_gmt":"2012-07-09T16:04:06","slug":"light-science-and-magic","status":"publish","type":"post","link":"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=17721","title":{"rendered":"Light science and magic"},"content":{"rendered":"<p id=\"top\" \/><em>Fill Hunter, Steven Biver, Paul Fuqua<\/em><\/p>\n<h4>Light, the raw material of photography<\/h4>\n<ul>\n<li>Why does the contrast of the light have such a dramatic effect on the appearance of the highlight on the bottle but almost no effect on the pepper? As you look at the examples, you already know that the difference in the lighting is caused by the subject itself. p.23 <em>Material perception differs for different materials, since material appearance may be more or less invariant to lighting.<\/em><\/li>\n<li>Translucent subjects are of little special importance to photographers because their translucence usually requires no special lighting consideration. This is because they always absorb some of the light and reflect some of the light, in addition to transmitting it. p.27 <em>What about back-lighting?<\/em><\/li>\n<\/ul>\n<h4>The management of reflection and the family of angles<\/h4>\n<ul>\n<li> All white things produce a great deal of diffuse reflection. We know this because they appear white regardless of the angle from which we view them. (Walk around the room you are in now. Look at the white objects and the black objects from different angles. Notice that the apparent brightness of the black objects may change with viewpoint, but the white objects stay about the same.)  p.33 <em>This is a nice way to distinguish between a white object and a shiny one. <\/em><\/li>\n<li>So we now have seen that neither the angle nor the size of the light source affects the appearance of a diffuse reflection. However, the distance from the light to the surface of the subject does matter. The closer the light gets to the subject, the brighter the subject becomes and, at a given exposure setting, the lighter the subject appears in the finished picture. p.36<\/li>\n<li>The brightness of the image of a direct reflection is the same regardless of the distance from the source. [&#8230;] Notice, however, that the size of the reflection of the lamp does change. This change in size keeps the inverse square law from being violated. p.38 <em>Could this be used to retrieve light distance to the subject?<\/em><\/li>\n<li>Fig 3.5 &amp; 3.6<em>. <\/em>p.39<em> The comb not only is highly variant in terms of material appearance, but its shape also seems to change!<\/em><\/li>\n<li>A viewer looking at a surface sees each of these points at a slightly different angle. Taken together, these different angles make up the family of angles that produces direct reflection. In theory, we could also talk about the family of angles that produces diffuse reflection. However, such an idea would be meaningless because diffuse reflection can come from a light source at any angle. Therefore, when we use the phrase family of angles we will always mean those angles that produce direct reflection. p.40 <em>This is without taking into account local occlusions!<\/em><\/li>\n<\/ul>\n<p><em><a href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2011\/08\/Mask-all.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-thumbnail wp-image-17981\" title=\"Mask-all\" src=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2011\/08\/Mask-all-150x150.jpg\" alt=\"\" width=\"150\" height=\"150\" \/><\/a><a href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2011\/08\/Mask-polar.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-thumbnail wp-image-17991\" title=\"Mask-polar\" src=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2011\/08\/Mask-polar-150x150.jpg\" alt=\"\" width=\"150\" height=\"150\" \/><\/a><a href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2011\/08\/Mask-unpolar.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-thumbnail wp-image-18001\" title=\"Mask-unpolar\" src=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2011\/08\/Mask-unpolar-150x150.jpg\" alt=\"\" width=\"150\" height=\"150\" \/><\/a><br \/>\n<\/em><\/p>\n<h4>Surface appearances<\/h4>\n<ul>\n<li>One of the first steps in lighting a scene is to look at the subject and decide what kind of reflection causes the subject to appear the way it does. The next step is to position the light, the subject, and the camera to make the photograph capitalize on that type of reflection and minimize the others. p.50 <em>Ultimately depends on intent.<\/em><\/li>\n<li>We could offer you mathematical formulas to calculate an acceptable distance between the light and the subject at any given angle (and for any given acceptable side-to-side exposure error). p.58 <em>Nice first guess for light placement!<\/em><\/li>\n<li>The solution is to move the light to a very shallow angle to the surface so that it skims across, as seen in Figure 4.15. This gives each particle of texture a highlight side and a shadow side. p.63 <em>Another first guess that may be in conflict with the previous one if the goal is to not show texture.<\/em><\/li>\n<li>The texture in this type of surface can be helped still more if we use as small a light source as possible. This is because small light sources produce sharply defined shadows. If the particles of texture are tiny, their image may be too small to resolve sharply. p.63 <em>Could make light source parameters change to better reveal various surface details when rotated!<\/em><\/li>\n<li>Notice that this arrangement could not be more different from the one that worked well for the white cloth. Instead of raking the light from the side, we have put it above the subject. This nearly eliminates the small shadows that defined the cloth texture. Instead of a small light source, we have a large one. p.66 <em>Diffuse reveals form through dark tones, while reflections reveal shape through bright tones!<\/em><\/li>\n<li>The only remedy for this problem is a small gobo that fills the family of angles that causes direct reflection on the label but that is not large enough to extend into the family of angles that produces direct reflection on the rest of the subject. (Gobo is photospeak for anything that goes between the subject and the light source specifically to block part of the light.) p.73<\/li>\n<li>Figure 4.26 is a piece of highly polished wood lit to produce both direct and diffuse reflection. A medium-sized light source has been positioned to reflect in the lower portion of the wooden surface to show the glossy finish. Notice that the slight physical texture in the surface is also revealed by the direct reflection.  p.75 <em>The edge of the highlight reveals shape.<\/em><\/li>\n<\/ul>\n<h4>Revealing shape and contour<\/h4>\n<ul>\n<li>The most obvious solution to this problem is to add another light to fill in some of the shadow. This is not always the best solution, nor is it always necessary. [&#8230;] But placing the fill light over the camera may light the subject too evenly. That costs the very depth we are trying to achieve. [&#8230;] We can avoid adding problems by using a fill light that is as soft as possible and as dim as possible, provided it is still bright enough to do its job. p.93<\/li>\n<li>Sometimes we have to add more fill from a white light source to overcome the color cast caused by the background surface. We may also need to cover part of the background surface with black cards to get rid of off-color reflected fill. p.95 <em>Color bleeding <\/em><em>may sometimes be avoided.<\/em><\/li>\n<li>Finally, remember that surface detail, subtle variations in both color and texture, are most visible in the mid-ranges. p.101 <em>May show small details in the mid-range, and bigger protrusions via shadows and highlights.<\/em><\/li>\n<\/ul>\n<p><em><a href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2011\/08\/Doll-unfill.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-thumbnail wp-image-17971\" title=\"Doll-unfill\" src=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2011\/08\/Doll-unfill-150x150.jpg\" alt=\"\" width=\"150\" height=\"150\" \/><\/a><a href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2011\/08\/Doll-fill.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-thumbnail wp-image-17961\" title=\"Doll-fill\" src=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2011\/08\/Doll-fill-150x150.jpg\" alt=\"\" width=\"150\" height=\"150\" \/><\/a><a href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2011\/08\/Doll-diff.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-thumbnail wp-image-17951\" title=\"Doll-diff\" src=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2011\/08\/Doll-diff-150x150.jpg\" alt=\"\" width=\"150\" height=\"150\" \/><\/a><br \/>\n<\/em><\/p>\n<h4>Metal<\/h4>\n<ul>\n<li>Bright or Dark? One of the first decisions that we have to make when we photograph a piece of metal is how bright we want it to be. Do we want it to be bright, dark, or something in between? The answer to this question determines the lighting. p.113 <em>It seems that both polarities are okay for metals. This may be because although there is an quasi-invariant<\/em> <em>for diffuse durfaces (dark tones in concavities), there cannot be one for metals since reflections may fall anywhere (if ignoring inter-reflections).<\/em><\/li>\n<li>Changing the distance of the light source changes the brightness of the background but not of the metal. This seems to give us nearly infinite control of the relative brightness of the two. Sometimes it does, but not always. This is because the focal length of the lens can also indirectly influence the effective size of the light. p.128 <em>Thus if we are allowed to move a bit the viewpoint, we have more degrees of freedom.<\/em><\/li>\n<li>However, we have also said that the black plastic is glossy. And we know that glossy things do produce direct reflection, even if they are too black to produce diffuse reRection. This means that we can light the metal by bouncing light off the plastic surface as in Figure 6.27. p.138 <em>Thus if we are allowed to change the material of &#8220;background&#8221; objects  (that appear in the image as opposed to cards and gobos), we can take  advantage of multiple bounces in light placement ! <\/em><\/li>\n<\/ul>\n<p><em><a href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2011\/08\/Spatula_bright.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-thumbnail wp-image-18011\" title=\"Spatula_bright\" src=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2011\/08\/Spatula_bright-150x150.jpg\" alt=\"\" width=\"150\" height=\"150\" \/><\/a><a href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2011\/08\/Spatula_Dark.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-thumbnail wp-image-18021\" title=\"Spatula_Dark\" src=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2011\/08\/Spatula_Dark-150x150.jpg\" alt=\"\" width=\"150\" height=\"150\" \/><\/a><a href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2011\/08\/Spatula_NegBlend.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-thumbnail wp-image-18031\" title=\"Spatula_NegBlend\" src=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/wp-content\/uploads\/2011\/08\/Spatula_NegBlend-150x150.jpg\" alt=\"\" width=\"150\" height=\"150\" \/><\/a><br \/>\n<\/em><\/p>\n<h4>The case of the disappearing glass<\/h4>\n<ul>\n<li> When we light metal, we are primarily interested in the surfaces facing the camera. If they look right. then minor adjustments can usually take care of the details. Lighting glass, however, requires attention to the edges. If the edges are clearly defined, we can often ignore the front surface, altogether. p.149 <em>Refractions are important too!<\/em><\/li>\n<li>If we want to produce a picture that clearly and pleasingly reproduces the glassware, we must do the following: 1) Produce strong lines along the edges of the subject. These lines delineate its shape and set it apart from the background. 2) Eliminate distracting reflections of the lights and other equipment we are using. p.151 <em>May surface details be lost?<\/em><\/li>\n<\/ul>\n<h4>The extremes<\/h4>\n<ul>\n<li> More often, white-on-white subjects are only slightly darker than the background, and we dare not further brighten them with fill. Instead, we usually add a black card, again to one side. This blocks some of the light reflecting from the background and produces a shadowed side to the subject. p.249 <em>The choice to use gobo\/black cards versus light\/white cards also depends on the subject material.<\/em><\/li>\n<li>We have explained why direct reflections are usually not very important to white subjects. The few we see are generally helpful to add a bit of dimension, but compared with the diffuse reflections, they tend to be too weak to be major players in the lighting event. p.254<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Fill Hunter, Steven Biver, Paul Fuqua Light, the raw material of photography Why does the contrast of the light have such a dramatic effect on the appearance of the highlight on the bottle but almost no effect on the pepper? As you look at the examples, you already know that the difference in the lighting &#8230; <a title=\"Light science and magic\" class=\"read-more\" href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=17721\" aria-label=\"Read more about Light science and magic\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[621],"tags":[],"class_list":["post-17721","post","type-post","status-publish","format-standard","hentry","category-books"],"_links":{"self":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/17721","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=17721"}],"version-history":[{"count":11,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/17721\/revisions"}],"predecessor-version":[{"id":22751,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/17721\/revisions\/22751"}],"wp:attachment":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=17721"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=17721"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=17721"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}