https://svn.lrde.epita.fr/svn/oln/branches/cleanup-2008/milena Index: ChangeLog from Nicolas Ballas <ballas@lrde.epita.fr> Add documentation about the image values. * doc/tutorial/image_values.txt: New, doc file. image_values.txt | 234 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 234 insertions(+) Index: doc/tutorial/image_values.txt --- doc/tutorial/image_values.txt (revision 0) +++ doc/tutorial/image_values.txt (revision 0) @@ -0,0 +1,234 @@ +-*- outline -*- + + +* Image Values + +An image is an application: + ima: Domain -> Destination + p -> ima(p) + +Domain is a set of the point, or more generally sites, that compose the +image. Destination is a set containing the values of the image. Each value +of the image belongs to the Destination set. + +Yet, Destination can have several definitions. In the following, we will +details these definitions. + + + +** E: values space + +E is a mathematical set. It contains, at least, all the values that the image +can possibly take. All the image values are in the value spaces E. +So for all p, ima(p) belongs to E. +For instance, the value space of an image can be the rgb set, the int_u8 set +or the gl8 set(gray level coded on 8 bits)... + +All the image provide the method .destination() which returns E. +However, E is not always iterable in Milena. For performance issues, E is +iterable only if the value are coded on less than 24 bits. + +If E is iterable, the following code: + +Code A) + for all v in ima.destination() + print v; + +prints all the values contained in the values space. + +** V: eligible values set. + +Like E, V is a mathematical set. It contains all the values that the image can possibly take. So if v belongs to V, ima(p) <- v is possible without any +conversions. + +For instance, consider the set S composed by the colors RED, BLUE, ORANGE. +S = (RED, BLUE, ORANGE). + +S is a subset of the rgb set. Indeed, the colors RED, BLUE, ORANGE are members +of the rgb set. So, consider ima, an image defined with S as eligible value +set. ima admits the rgb set as values space (the rgb set is the superset of S). +However, ima can take only value from the S set (and not from the rgb set). So, +ima(p) <- WHITE will not work. + +All the image provide the method .values_eligible() which returns S. + +Why do we introduce the eligible value set, since its definition is close to +the value space? +In the previous example, we can't apply Code A on ima. For performance reasons, +we don't want to iter on the rgb set. But, it is possible to iterate over the +ima values; since the ima eligible values set is a restriction of the rgb set. + +If we apply the following code on ima, + +code B) + for all v in ima.values_eligible() + print v + +the result will be: + RED BLUE ORANGE + +V can also be the value spaces itself. An image cab have all the rgb colors as +eligible values. In this case, we can't iterate over the image eligible values. + + +** Vp: values taken set + +Vp is a mathematical set that contains the values currently taken by an image. +So for all p in the image domain, ima(p) belongs to Vp. +If an image provides the access to its Vp, the image interface has the +method .values_taken() which returns its Vp. + + +For instance consider the following 2d image: + + ----- +| R | R stands for Red +| BGB| B stands for Blue +| OO | G stands for Green + ----- O stands for orange. + + +The following code: + +code C) + for all v in ima.values_taken() + print v + +prints: + +RBGO + +If the image admits (RED, BLUE, GREEN, WHITE, ORANGE) as eligible values set, +the code B results is: +RBGWO (W stands for white). + + + + +** C: value cells + +All the milena image types are composed by cell. +A cell is a location in RAM or in a file that stores an image value. + +For instance consider the following 2d images: + + 0 1 2 3 4 + ---------- +0 | | +1 | R G R | +2 | | +3 | O W| +4 | | + ---------- + +This image is composed by 5 cells: R, G, R, O, W. +Each cell correspond to a point 2d (respectively (1, 1), (1, 2), (1, 3), +(1, 4)). + + +C is the list of cells that is currently composing the image. +Some image types provide an access to the cells list through the method +.values_cell() which returns C. + +For instance, if we apply the following code the the previous image: + +code D) + for all v in ima.values_cells() + print v + +the result will be: +RGROW, we print the list of cells composing the image. + +C is not a mathematical set. Indeed, in cell list a member can be duplicate. +In the previous example R is present twice in the cells list. + +* Example1 + +Consider the following rle image: + +ima = ----- + | R | + | BBB| + | OO | + | RR| + ----- + +This image encoded by runs (a run is a succession of points). +Furthermore, only one value is associated to each run. + +So, in memory, the image will be encoded this way: + +ima = ({p, {R, 1}}, {q, {B, 3}}, {r, {O, 2}}, {s, {R, 2}} ) + ^^^ ^^^ ^^^ + run start run value run len + +where p, q, r are point at the beginning of a run: + ----- + | p | + | q | + | r | + | s | + ----- + +The run values correspond to the image cells. +So if we apply the code D to this image, the result will be: +RBOR + +If we apply the code C to this image, the result will be: +RBO + +* Example2 + +Consider the following sparse image: + +ima = ----- + | R | + | BGB| + | OG | + | RR| + ----- + +This image is also encoded by runs. +But here, several values can be associated to each run. + +So, in memory, the image will be encoded this way: + +ima = ({p, (R)}, {q, (B, G, B)}, {r, {O, G}}, {s, {R, R}} ) + ^^^ ^^^ ^^^ + run start run values + +where p, q, r are point at the beginning of a run. + +The different values in each run correspond to the image cells. +So if we apply the code D to this image, the result will be: +RBGBOGRR + +If we apply the code C to this image, the result will be: +RGBO + +* Example3 + +Consider the following 2d image: + +ima = ----- + |GROOG| + |BRBGB| + ----- + +Every pixel can have a different values, so all the pixels are stored in +memory.Thus, a cell is associated to each pixel of the image. +So if we apply the code D to this image, the result will be: +GROOGBRBGB + +If we apply the code C to this image, the result will be: +RGBO + + +* Order relationship + +E <= V <= V = E* + + +* Image properties related to the values + +FIXME