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مبادئ الإضاءة ..
الشكل والشكل
FORM AND SHAPE
We have used the word " form " rather freely in our discussion up to this point without bothering to give it a precise meaning . We have also made the categorical statement that both light and shade are necessary to depict form . It might be well , at this point , to stop for a moment and see what we actually mean by form . There is a good deal of confusion on this point , and since form will be used repeatedly throughout this Assignment much of what follows will not have its full meaning unless we come to a common understanding of our basic term .
Form is not a simple concept It is not easily defined , nor is its definition easily grasped . It may be better , therefore , to discuss what is meant by form rather than define it technically , since definitions have a habit of employing terms which themselves need further definition , so that the end result is too often a highly condensed statement which , while technically accurate , is no more informative than the term being defined .
Form , as used here , is much more than a synonym for shape . It takes into account not only the outward appearance of a thing , but also its structural meaning and significance . A portrait , for example , or a figure study does not truly depict form unless it also gives an insight into the skeletal structure of the subject . Painters consider a study of anatomy of extreme importance , since without a knowledge of the basic structure of the human body , it is not possible to truly depict its form .
Shape , on the other hand , is a more superficial sort of thing . Shape deals with the outer configuration and appearance of an object . In nature , form and shape are generally consistent with each other . The shape of a normal hand , for example , gives a very good indication of its internal skeletal and muscular structure . That is why scientists can successfully reconstruct complete animals .
from skeletal remains . In man - made objects , this close harmony between form and shape does not necessarily exist . Modern functional design has , as one of its basic requirements , the creation of external shapes that supplement and are consistent with internal structure and function . Victorian ornamentation , on the other hand , usually succeeds in hiding or effacing form .
Our frame of reference is photography . Our discussion must , therefore , be carried on from that point of view and take into consideration the special characteristics and limitations of the photographic medium . While there is a strong fundamental parallel between photography and , let us say , painting as a means of dealing with form , there are important differences as well . The parallelism will cause the photographer and painter to define form in similar but not identical terms ; the differences will be reflected in differences in interpretations and in useage .
The painter deals more intimately with form than does the photographer . He constructs his basic forms first , generally in his rough sketches or outlines , and then clothes them in their outward shapes . One of his most important problems is to clothe or cover his forms with shapes that are correct and consistent . The photographer has no such problem . His subject is ready made and he cannot alter it . He must , therefore , start with the premise that the outward shape of his subject is correct and true to the form that it clothes . ( This , of course , is quite frequently an invalid assumption , but in that case the falsity . not the photographer's but the designer's . ) The photographer's problem is to light the subject in such a manner that his representation of its outward shape will reveal its basic form .
The photographer's concern in lighting for form stems from the nature of his medium . In real life , we are aware of only a small fraction of what we see . The eye quickly moves over any object in its field , selecting only the significant detail and seeing but vaguely , if at all , the great mass of subordinate and uninteresting material as of no consequence . The camera has no such power of discrimination . Everything in its field of view is recorded with full impartiality . The result , almost invariably , is a catalog of detail rather than an evaluation of form . The photographer must supply the discrimination the camera lacks , and he does so largely by his control of lighting .
Let us perform a few simple experiments in light control to see how this works out in actual practice .
Set up a white card and an incandescent bulb at some distance from it , as shown in Figure 1 .
If the lamp is far enough away , the light over the entire surface of the card will be substantially uniform as far as the eye can judge . Tilt the card so that it is at a considerable angle , but leave everything else alone . We now have the condition shown in Figure 2 .
If you watch closely as you tilt the card , you will notice that its brightness decreases as its angle to the lamp increases . This is due to the fact that the card is receiving less light . In Figure 1 , all the light included in angle A reaches the card , but in Figure 2 , the card receives the light from the smaller angle B. This
Figure 1 White card set up so it is uniformly lighted by an incandescent bulb .
Figure 2 White card at samet distance as Figure 1 but tilted at a considerable angle .
Figure 3 White card at same angle to light as in Figure 2 but at half the distance .
demonstrates that the smaller the angle presented to the light source , the lower the visual brightness . You may not have been consciously aware of the truth of this statement before this experiment was performed but , nevertheless , you knew it and you used that knowledge in evaluating the form of any object you were looking at .
At this stage of our experiment , if you didn't know the location of the lamp , you could not tell whether the lesser brightness of the card in Figure 2 was caused by its angle to the light source , its greater distance from the light , or simply whether the card itself was a light gray instead of white . All of these conditions would bring about the same result ..
Now let us bring the light much closer to the card as in Figure 3. The distance from the lamp to the near edge of the card is considerably less than to the far edge , and this difference will show up as a gradual change of brightness from one end of the card to the other , as illustrated in Figure 4 .
The variation in light intensity on our test object gives us a number of important clues as to its shape and the location of the light source . We conclude that the surface of our card is flat and uniform , since only this type of surface would give the uniform tone gradation we are getting . We also conclude that the light source is at an angle and quite close to the card to account for the strong shading off from maximum to minimum brightness . It is important to note that it is the variation in light intensity that makes these conclusions possible .
Figure 4 Illustration of fall - off of light on surface as it recedes from light source .
Now let us set up a white cube with the light source off to one side and higher than the cube . The photograph we get under those circumstances is shown in Figure 5 .
Viewed from the front , we see three surfaces . Each surface has a different degree of brightness . The variation in brightness over the cube's surfaces gives us important evidence as to its shape and the location of the light source . Let us go through the reasoning , step by step , that enables us to arrive at our conclusions .
The top is the brightest side , which tells us that this surface is nearest the light source , or is at less of an angle to it than the other two sides . The front is intermediate in tone , and this tells us that the light is in front of the cube as well as above it . The right side is darkest and is , therefore , farther from and at a greater . angle to the light than the other two sides .
Each of the three surfaces is uniformly illuminated , so we conclude that the light is at a considerable distance in relation to the size of the cube and also that each surface is smooth and regular . The boundary of each surface is made up of sharp , straight lines . This tells us that each edge is sharp and straight . All in all , we know quite a bit about our test object simply by noting how the light varies in intensity over its exposed surfaces .
Now let us examine Figure 6. This time there are no sharp straight lines . dividing the various surfaces . Instead , the front surface has a broadly defined highlight area which shades off gradually to areas of lower illumination to the right . We conclude , therefore , that the front surface presents a constantly and uniformly changing angle to the light - in other words , it is curved . The top surface , because its illumination is uniform , is obviously flat . We conclude , from this variation in light intensity , that our test object is a solid cylinder .
Figure SA Cube equally lighted from all sides so no clue of shape exists . This " object " could be a hexagonal cut out .
Figure 5 Cube lighted normally from upper left results in three degrees of brightness . These brightness differences give the clues as to the object's shape .
Figure 6 Object lighted from upper left . The gradual darkening indicates a curved surface .
You might , at this point , say that we are a bit disingenuous in our arguments that we can recognize the shape of our test object by its outline without going into a lot of mental gymnastics . That may be true to a limited extent with the simple geometric shapes we have discussed here , but as we shall see , it is definitely not true when our shapes become complicated to any degree .
In Figure 7 , we have lighted a test cylinder so uniformly as to eliminate all tone variation insofar as the camera can see them . We can , for all we know , be looking at a sheet of paper or a card cut out to simulate a cylinder . Nevertheless , we would generally conclude that our test object is a solid cylinder rather than a card cut - out because we have no particular reason to suspect trickery and it isn't very often that we see cut - outs designed to simulate solid objects .
Figure 7 Even though we know this object to be a cylinder , with the even lighting it could be paper cut out to simulate a cylinder .
Figure 8 The subject is the same as in Figure 7 , but the light now comes mainly from the left . The shadows on the right and top tell us that this is neither a paper cut - out nor the cylinder of Figure 6 .
A glance at Figure 8 will show beyond question that both conclusions about Figure 7 were wrong . We see now that it is not at all the same cylinder as in Figure 6. Instead , the top surface is cut into a series of ridges . What is more .
important to our discussion , we see these ridges only because of the interplay of light and shade over their surfaces .
Up to this point we have dealt only with completely diffuse , neutral white surfaces . Such surfaces , however , are rare . Most surfaces have some degree of specularity that is , they are more or less shiny , and all surfaces absorb some part of the light striking them , so they have some tone value .
مبادئ الإضاءة ..
الشكل والشكل
FORM AND SHAPE
We have used the word " form " rather freely in our discussion up to this point without bothering to give it a precise meaning . We have also made the categorical statement that both light and shade are necessary to depict form . It might be well , at this point , to stop for a moment and see what we actually mean by form . There is a good deal of confusion on this point , and since form will be used repeatedly throughout this Assignment much of what follows will not have its full meaning unless we come to a common understanding of our basic term .
Form is not a simple concept It is not easily defined , nor is its definition easily grasped . It may be better , therefore , to discuss what is meant by form rather than define it technically , since definitions have a habit of employing terms which themselves need further definition , so that the end result is too often a highly condensed statement which , while technically accurate , is no more informative than the term being defined .
Form , as used here , is much more than a synonym for shape . It takes into account not only the outward appearance of a thing , but also its structural meaning and significance . A portrait , for example , or a figure study does not truly depict form unless it also gives an insight into the skeletal structure of the subject . Painters consider a study of anatomy of extreme importance , since without a knowledge of the basic structure of the human body , it is not possible to truly depict its form .
Shape , on the other hand , is a more superficial sort of thing . Shape deals with the outer configuration and appearance of an object . In nature , form and shape are generally consistent with each other . The shape of a normal hand , for example , gives a very good indication of its internal skeletal and muscular structure . That is why scientists can successfully reconstruct complete animals .
from skeletal remains . In man - made objects , this close harmony between form and shape does not necessarily exist . Modern functional design has , as one of its basic requirements , the creation of external shapes that supplement and are consistent with internal structure and function . Victorian ornamentation , on the other hand , usually succeeds in hiding or effacing form .
Our frame of reference is photography . Our discussion must , therefore , be carried on from that point of view and take into consideration the special characteristics and limitations of the photographic medium . While there is a strong fundamental parallel between photography and , let us say , painting as a means of dealing with form , there are important differences as well . The parallelism will cause the photographer and painter to define form in similar but not identical terms ; the differences will be reflected in differences in interpretations and in useage .
The painter deals more intimately with form than does the photographer . He constructs his basic forms first , generally in his rough sketches or outlines , and then clothes them in their outward shapes . One of his most important problems is to clothe or cover his forms with shapes that are correct and consistent . The photographer has no such problem . His subject is ready made and he cannot alter it . He must , therefore , start with the premise that the outward shape of his subject is correct and true to the form that it clothes . ( This , of course , is quite frequently an invalid assumption , but in that case the falsity . not the photographer's but the designer's . ) The photographer's problem is to light the subject in such a manner that his representation of its outward shape will reveal its basic form .
The photographer's concern in lighting for form stems from the nature of his medium . In real life , we are aware of only a small fraction of what we see . The eye quickly moves over any object in its field , selecting only the significant detail and seeing but vaguely , if at all , the great mass of subordinate and uninteresting material as of no consequence . The camera has no such power of discrimination . Everything in its field of view is recorded with full impartiality . The result , almost invariably , is a catalog of detail rather than an evaluation of form . The photographer must supply the discrimination the camera lacks , and he does so largely by his control of lighting .
Let us perform a few simple experiments in light control to see how this works out in actual practice .
Set up a white card and an incandescent bulb at some distance from it , as shown in Figure 1 .
If the lamp is far enough away , the light over the entire surface of the card will be substantially uniform as far as the eye can judge . Tilt the card so that it is at a considerable angle , but leave everything else alone . We now have the condition shown in Figure 2 .
If you watch closely as you tilt the card , you will notice that its brightness decreases as its angle to the lamp increases . This is due to the fact that the card is receiving less light . In Figure 1 , all the light included in angle A reaches the card , but in Figure 2 , the card receives the light from the smaller angle B. This
Figure 1 White card set up so it is uniformly lighted by an incandescent bulb .
Figure 2 White card at samet distance as Figure 1 but tilted at a considerable angle .
Figure 3 White card at same angle to light as in Figure 2 but at half the distance .
demonstrates that the smaller the angle presented to the light source , the lower the visual brightness . You may not have been consciously aware of the truth of this statement before this experiment was performed but , nevertheless , you knew it and you used that knowledge in evaluating the form of any object you were looking at .
At this stage of our experiment , if you didn't know the location of the lamp , you could not tell whether the lesser brightness of the card in Figure 2 was caused by its angle to the light source , its greater distance from the light , or simply whether the card itself was a light gray instead of white . All of these conditions would bring about the same result ..
Now let us bring the light much closer to the card as in Figure 3. The distance from the lamp to the near edge of the card is considerably less than to the far edge , and this difference will show up as a gradual change of brightness from one end of the card to the other , as illustrated in Figure 4 .
The variation in light intensity on our test object gives us a number of important clues as to its shape and the location of the light source . We conclude that the surface of our card is flat and uniform , since only this type of surface would give the uniform tone gradation we are getting . We also conclude that the light source is at an angle and quite close to the card to account for the strong shading off from maximum to minimum brightness . It is important to note that it is the variation in light intensity that makes these conclusions possible .
Figure 4 Illustration of fall - off of light on surface as it recedes from light source .
Now let us set up a white cube with the light source off to one side and higher than the cube . The photograph we get under those circumstances is shown in Figure 5 .
Viewed from the front , we see three surfaces . Each surface has a different degree of brightness . The variation in brightness over the cube's surfaces gives us important evidence as to its shape and the location of the light source . Let us go through the reasoning , step by step , that enables us to arrive at our conclusions .
The top is the brightest side , which tells us that this surface is nearest the light source , or is at less of an angle to it than the other two sides . The front is intermediate in tone , and this tells us that the light is in front of the cube as well as above it . The right side is darkest and is , therefore , farther from and at a greater . angle to the light than the other two sides .
Each of the three surfaces is uniformly illuminated , so we conclude that the light is at a considerable distance in relation to the size of the cube and also that each surface is smooth and regular . The boundary of each surface is made up of sharp , straight lines . This tells us that each edge is sharp and straight . All in all , we know quite a bit about our test object simply by noting how the light varies in intensity over its exposed surfaces .
Now let us examine Figure 6. This time there are no sharp straight lines . dividing the various surfaces . Instead , the front surface has a broadly defined highlight area which shades off gradually to areas of lower illumination to the right . We conclude , therefore , that the front surface presents a constantly and uniformly changing angle to the light - in other words , it is curved . The top surface , because its illumination is uniform , is obviously flat . We conclude , from this variation in light intensity , that our test object is a solid cylinder .
Figure SA Cube equally lighted from all sides so no clue of shape exists . This " object " could be a hexagonal cut out .
Figure 5 Cube lighted normally from upper left results in three degrees of brightness . These brightness differences give the clues as to the object's shape .
Figure 6 Object lighted from upper left . The gradual darkening indicates a curved surface .
You might , at this point , say that we are a bit disingenuous in our arguments that we can recognize the shape of our test object by its outline without going into a lot of mental gymnastics . That may be true to a limited extent with the simple geometric shapes we have discussed here , but as we shall see , it is definitely not true when our shapes become complicated to any degree .
In Figure 7 , we have lighted a test cylinder so uniformly as to eliminate all tone variation insofar as the camera can see them . We can , for all we know , be looking at a sheet of paper or a card cut out to simulate a cylinder . Nevertheless , we would generally conclude that our test object is a solid cylinder rather than a card cut - out because we have no particular reason to suspect trickery and it isn't very often that we see cut - outs designed to simulate solid objects .
Figure 7 Even though we know this object to be a cylinder , with the even lighting it could be paper cut out to simulate a cylinder .
Figure 8 The subject is the same as in Figure 7 , but the light now comes mainly from the left . The shadows on the right and top tell us that this is neither a paper cut - out nor the cylinder of Figure 6 .
A glance at Figure 8 will show beyond question that both conclusions about Figure 7 were wrong . We see now that it is not at all the same cylinder as in Figure 6. Instead , the top surface is cut into a series of ridges . What is more .
important to our discussion , we see these ridges only because of the interplay of light and shade over their surfaces .
Up to this point we have dealt only with completely diffuse , neutral white surfaces . Such surfaces , however , are rare . Most surfaces have some degree of specularity that is , they are more or less shiny , and all surfaces absorb some part of the light striking them , so they have some tone value .
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