10224 withColorResolutionReducedBy:numBits

 10225     "return a new image with the same picture as the receiver, but reduced colorResolution;

 10226      that is, the lower numBits are cleared in the r/g/b color components.

 10227      If anything fails, return nil."

 10228 

 10229     |xMax yMax r g b nR nG nB clr pix map revMap n_clr n_pix mask anyChange

 10230      newColors newColorArray newImage extMask extBits newPixelValue|

 10231 

 10232     numBits > 7 ifTrue:[

 10233         ^ nil

 10234     ].

 10235     mask := (16rFF bitShift:numBits) bitAnd:16rFF.

 10236     extMask := (1 bitShift:numBits).

 10237     extBits := extMask - 1.

 10238 

 10239     anyChange := false.

 10240 

 10241     newColors := Set new.

 10242     newColorArray := OrderedCollection new.

 10243     map := Array new:256.

 10244     revMap := OrderedCollection new.

 10245 

 10246     newImage := self class width:width height:height depth:depth.

 10247     newImage photometric:photometric.

 10248     newImage colorMap:(self colorMap copy).

 10249     newImage bits:(self bits copy).

 10250     newImage mask:(self mask copy).

 10251 

 10252     xMax := width - 1.

 10253     yMax := height - 1.

 10254 

 10255     newPixelValue := 

 10256         [:image :pixelValue |

 10257             |r g b nR nG nB|

 10258 

 10259             r := image redBitsOf:pixelValue.

 10260             g := image greenBitsOf:pixelValue.

 10261             b := image blueBitsOf:pixelValue.

 10262             nR := r bitAnd:mask. (nR bitAnd:extMask)~~0 ifTrue:[nR := nR bitOr:extBits].

 10263             nG := g bitAnd:mask. (nG bitAnd:extMask)~~0 ifTrue:[nG := nG bitOr:extBits].

 10264             nB := b bitAnd:mask. (nB bitAnd:extMask)~~0 ifTrue:[nB := nB bitOr:extBits].

 10265             image valueFromRedBits:nR greenBits:nG blueBits:nB.

 10266         ].

 10267 

 10268 

 10269     photometric == #palette ifFalse:[

 10270         "/ direct manipulation of the pixels

 10271         0 to:yMax do:[:y |

 10272             0 to:xMax do:[:x |

 10273                 pix := self pixelAtX:x y:y.

 10274                 n_pix := newPixelValue value:self value:pix.

 10275                 n_pix ~= pix ifTrue:[

 10276                     newImage pixelAtX:x y:y put:n_pix.

 10277                     anyChange := true.

 10278                 ]

 10279             ]

 10280         ].

 10281         anyChange ifFalse:[

 10282             ^ nil

 10283         ].

 10284     ] ifTrue:[

 10285         "/ manipulate the colormap

 10286         0 to:yMax do:[:y |

 10287             0 to:xMax do:[:x |

 10288                 pix := self pixelAtX:x y:y.

 10289                 (n_pix := map at:pix+1) isNil ifTrue:[

 10290                     clr := self colorAtX:x y:y.

 10291 

 10292                     r := clr redByte.

 10293                     g := clr greenByte.

 10294                     b := clr blueByte.

 10295                     nR := r bitAnd:mask. (nR bitAnd:extMask)~~0 ifTrue:[nR := nR bitOr:extBits].

 10296                     nG := g bitAnd:mask. (nR bitAnd:extMask)~~0 ifTrue:[nR := nR bitOr:extBits].

 10297                     nB := b bitAnd:mask. (nR bitAnd:extMask)~~0 ifTrue:[nR := nR bitOr:extBits].

 10298                     n_clr := Color redByte:nR greenByte:nG blueByte:nB.

 10299                     (newColors includes:n_clr) ifFalse:[

 10300                         newColors add:n_clr.

 10301                         newColorArray add:n_clr.

 10302                         revMap add:pix.

 10303                         map at:pix+1 put:(n_pix := revMap size - 1).

 10304                     ] ifTrue:[

 10305                         "/ mhmh - multiple pixels mapped to the same color

 10306                         n_pix := (newColorArray indexOf:n_clr) - 1.

 10307                         map at:pix+1 put:n_pix.

 10308                     ]

 10309                 ].

 10310                 newImage pixelAtX:x y:y put:n_pix.

 10311             ]

 10312         ].

 10313         revMap size == self colorMap size ifTrue:[

 10314             revMap = (0 to:revMap size-1) ifTrue:[

 10315                 ^ nil

 10316             ]

 10317         ].

 10318 

 10319         newImage colorMap:(MappedPalette withColors:newColorArray).

 10320     ].

 10321 

 10322     ^ newImage

 10323 !

 10324