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+===== Implementing Pixmap support =====
+Submitted by ChristianHaider on Thu, 2011-09-01 10:48
+(this is for collecting my thoughts)
+I need to implement shadows for a client. The example was created with Illustrator CS5 and has a couple of pixmaps for painting and soft masks (transparency). I have to analyse the pixmaps in order to reconstruct the shadow algorithm of Illustrator (called "Schlagschatten" in Germen; could be "cast shadow" in English).
+Therefore, I need to read the pixmaps from the PDF - and being able to write them when I create them. PDF defines Images (/ImageXObject) as rectangular grid of colour values. An image is organized in rows: the first value is the colour in the top left corner with coordinates 1 @ 1. The next value is the next colour in the row right beside the last at 2 @ 1 and so on. The size of the rows is given by the required attribute /Width of /ImageXObject. The number of rows is given with /Height. The colour value in each cell is defined by the /ColorSpace attribute which knows how many components a colour in this space has (f.ex. /DeviceRGB has 3 components, /DeviceCMYK has 4, /Indexed and /DeviceGray 1). The size of one component is given by /BitsPerComponent.
+Therefore, I need to implement colour spaces properly, i.e. have a real colour space object after reading. I have defined all colour space classes grouped in Families as Values as placeholders for the real ones when I need them. The objective of this first implementation was to have /DeviceCMYK and /DeviceGray colour space objects which know how to set the stroking and filling colours in a renderer. Now I have to do this right.
+Unfortunately, colour space types dont follow the Smalltalk class hierarchy very well. The current implementation has two hierarchies: for Values and for Objects. Dictionary is defined as Object and serves as super class for most PDF objects. Especially Stream is a Dictionary which is super class to many PDF objects. So far, the Smalltalk hierarchy worked well except for two monsters: /Function and /Shading. There are 4 types of /Function where 2 are Dictionaries and 2 are Streams. /Shading has 7 types with 3 Dictionaries and 4 Streams. I got away with that by defining the attributes for both subhierarchies. F.ex. a /Function attribute would have
+    <type: #FunctionDictionary>
+    <type: #FunctionStream>
+This is clearly not as good as saying
+    <type: #Function>.
+With colour spaces this is even worse, because they can be Names or Arrays:
+<html>
+<ul><li> Device colour spaces
+<ul><li> <b>/DeviceGray</b>
+</li><li> <b>/DeviceRGB</b>
+</li><li> <b>/DeviceCMYK</b>
+</li></ul>
+</li><li> CIE based colour spaces
+<ul><li> <b>[/CalGray</b> <i>dictionary</i><b>]</b>
+</li><li> <b>[/CalRGB</b> <i>dictionary</i><b>]</b>
+</li><li> <b>[/Lab</b> <i>dictionary</i><b>]</b>
+</li><li> <b>[/ICCBased</b> <i>stream</i><b>]</b>
+</li></ul>
+</li><li> Special colour spaces
+<ul><li> <b>[Indexed</b> <i>base hival lookup</i><b>]</b>
+</li><li> <b>/Pattern</b> or <br><b>[/Pattern</b> <i>underlyingColourSpace</i><b>]</b>
+</li><li> <b>[/Separation</b> <i>name alternateSpace tintTransform</i><b>]</b>
+</li><li> <b>[/DeviceN</b> <i>names alternateSpace tintTransform</i><b>]</b> or <br><b>[/DeviceN</b> <i>names alternateSpace tintTransform attributes</i><b>]</b>
+</li></ul>
+</li></ul>
+</html>
+I will try the following implementation strategy: define the colour spaces as subclasses of **/Name** and **/Array** and add the abstract class **/ColourSpace**. Then the typing must be extended so that all the colour space classes scattered around the implementation hierarchy are recognized as being of type class **/ColourSpace**.
+The implementation hierarchy of colour spaces:
+<html>
+<ul><li> /Name
+<ul><li> <i><b>/DeviceColourSpace</b></i>
+<ul><li> <b>/DeviceGray</b>
+</li><li> <b>/DeviceRGB</b>
+</li><li> <b>/DeviceCMYK</b>
+</li></ul>
+</li><li> <b>/Pattern</b>
+</li></ul>
+</li><li> /Array
+<ul><li> <i><b>/CIEColourSpace</b></i>
+<ul><li> <b>/CalGray</b>
+</li><li> <b>/CalRGB</b>
+</li><li> <b>/Lab</b>
+</li><li> <b>/ICCBased</b>
+</li></ul>
+</li><li> <i><b>/SpecialColourSpace</b></i>
+<ul><li> <b>/Indexed</b>
+</li><li> <b>/UncolouredPattern</b>
+</li><li> <b>/Separation</b>
+</li><li> <b>/DeviceN</b>
+</li></ul>
+</li></ul>
+</li></ul>
+</html>
+Class **/ColourSpace** as new **/TypeClass**.
+<html>
+<ul><li> /Entity
+<ul><li> <b>/TypeClass</b>
+<ul><li> <b>/ColourSpace</b>
+</li><li> <i><b>/Function</b></i>
+</li><li> <i><b>/Shading</b></i>
+</li></ul>
+</li></ul>
+</li></ul>
+</html>
+A **/TypeClass** should not be instantiated, but serve as dispatcher for the type machinery.
+Now I need tests to see how this should look like in code...
+Lets see - I'll write a doc page for this: [[Typing]].