Home » Apple Manuals » Computer Software » Apple MA434Z/A » Manual Viewer

Apple MA434Z/A User Manual - Page 436

Nodes That Affect Premultiplication, Non-Black Premultiplied Images

UPC - 885909104239

Add to My Manuals
Save this manual to your list of manuals

Page 436 highlights

Nodes That Affect Premultiplication The following nodes can change the premultiplication status of an image, although anything that operates an image's mask differently from the RGB channels changes the effect. Node Color-ColorCorrect Color-Reorder Filter-DilateErode Key-LumaKey, DepthKey, DepthSlice Key-KeyLight Key-Primatte Layer-AddMix Layer-SwitchMatte Other-DropShadow Description This color corrector has an option in its Misc tab to specify when the incoming image is premultiplied. If it is, set the premultiplied parameter to yes. MDiv and MMult are internally inserted into the computation. This node allows you to switch a channel into the alpha channel, and may disrupt your premultiplication status. However, it isn't often used on images in the normal chain of color correct, position, and composite operations-but it is more of a utility node. This node is typically used to add to or chew the matte by a few pixels. Set your channels to just "a." Because you then modify the matte separately from the RGB, you make the image unpremultiplied. These keyers all have the option to immediately set your image to a premultiplied state. This keyer can output either a premultiplied or an unpremultiplied version, or just the alpha channel with the RGB untouched. This keyer can output either just the alpha or a premultiplied version. Setting it to unpremultiplied requires an external MDiv. This modified Over node allows you to manually break the premultiplied relationship by tweaking curves that specify how the matte multiplies the foreground and background images. It was inherited from another package, where it was used extensively because this particular system had no control over premultiplication. This node copies a channel from the second image to the alpha channel of the first image. You have the option to immediately premultiply the image (enabled by default). This node should be applied to premultiplied images only. Non-Black Premultiplied Images Some packages output images that are considered premultiplied, but in which the background is not black. This is mathematically bizarre. To work with these images, try the AEPremult macro included Chapter 32, "The Cookbook," on page 989. 436 Chapter 15 Image Processing Basics

Section	Page
Shake 4 User Manual	1
Contents	5
Shake 4 Documentation and Resources	15
What Is Shake?	15
Using the Shake Documentation	16
User Manual	16
Tutorials	16
Onscreen Help	16
Viewing Shake Onscreen Documentation on Linux Systems	16
Contextual Help	17
Apple Websites	17
Shake Websites	18
Keyboard and Mouse Conventions on Different Platforms	18
Using a Stylus	19
Window Navigation Using a Stylus	20
Using Dual-Head Monitors	20
Part I: Interface, Setup, and Input	21
An Overview of the Shake User Interface	23
Opening Shake	23
Opening Two Scripts at Once	23
Overview of the Shake User Interface	24
Getting Help in Shake	26
Making Adjustments to the Shake Window	27
Navigating in the Viewer, Node View, and Curve Editor	28
Saving Favorite Views	28
Working With Tabs and the Tweaker	30
Using the Tweaker	30
OS Window Functions	31
Menus and the Title Bar	31
Title Bar Information	31
Shake Menu (Mac OS X Only)	32
File Menu	32
Edit Menu	34
Tools Menu	34
Viewers Menu	35
Render Menu	35
Script Management	35
Customizing AutoSave	36
Changing the Possible Levels of Undo	37
The File Browser	38
Opening the File Browser	38
Navigating in the File Browser	39
Adding Directories to the Favorites List	40
Selecting Files	41
Viewing Controls	42
Specifying Media Placement	44
Additional Controls for Image Output	44
Using and Customizing Viewers	45
Using Multiple Viewers	46
Looking at Images in a Viewer	50
Suspending Rendering and Viewer Redraw	52
Controls in the Viewer Shelf	52
Using the Compare Buffers	57
Viewer Lookups, Viewer Scripts, and the Viewer DOD	61
Using the Viewer’s Domain of Definition (DOD)	67
Creating Your Own VLUTs and Viewer Scripts	68
Viewer Keyboard Shortcuts	68
The Viewer Shortcut Menu	69
Node-Specific Viewer Shelf Controls	70
The Parameters Tabs	72
Accessing a Node’s Controls Using the Parameters Tabs	72
Using Tweaker Windows	74
Global Parameters	74
Adjusting Parameter Controls	74
Using Expressions in Parameters	78
Linking One Parameter to Another	79
Combining Links With Expressions	79
Displaying Parameter Values in the Viewer	80
Copying and Pasting Script Code in Shake	80
The Parameters Tab Shortcut Menu	81
The Domain of Definition (DOD)	82
Assigning a DOD	83
Keying, Color Correcting, and the Background Color	85
The Time Bar	88
Setting a Script’s Frame Range	88
Playback Controls	89
Previewing Your Script Using the Flipbook	90
Setting a Script’s Global Parameters	91
About Global Parameters	91
Setting Global Variables From the Command Line	91
The Main Global Parameters	92
The Format Pop-Up Menu	94
Customizing the Format Pop-Up Menu	96
renderControls	96
guiControls	98
Monitor Controls	101
Colors	102
enhancedNodeView	102
Application Environmental Variables	104
Custom Variable Loading Order	104
Script Environmental Variables	104
Adding Media, Retiming, and Remastering	107
About Image Input	107
Adding Media to a Script	107
Dragging and Dropping Media Into Your Script	108
Image Sequence Numbering	108
Referring to Media Using File Paths	109
Using the FileIn (SFileIn) Node	110
FileIn Source Parameters	111
FileIn Timing Parameters	114
Pulldown and Pullup	116
Reintroducing 3:2 Pulldown After Transforming Media	117
Retiming	117
Fast versus Best Settings for Adaptive Retiming	120
Understanding the Retiming Parameters	123
The TimeX Node	123
Multiple Branches	124
Manual Manipulation of Time	125
Time Notation for a FileIn	125
Remastering Media	126
Fast versus Best In Remastering Parameters	127
Automatic Scene Detection for Multiple Shots	127
Convert Parameters	128
Working With Extremely High-Resolution Images	130
Adjusting the Cache for High-Resolution Images	131
Tuning the Amount of RAM Shake Uses	132
Using Shake With Final Cut Pro	132
How Sent Clips Are Arranged in Shake	133
Unsupported Media and Effects	134
Sending Clips From Final Cut Pro	135
The TimeRange of Scripts Generated From Final Cut Pro	136
Sending Media Back to Final Cut Pro	136
Using Proxies	137
Using Proxies	137
What Are Proxies?	137
Proxies and Final Low-Resolution Output Renders	137
Shake’s Three Proxy Methods	138
Using interactiveScale	139
Using Temporary Proxies	141
Changing the Aspect Ratio to 0.5	143
Customizing P1/P2/P3 for a Script or Session	143
Permanently Customizing Shake’s Proxy Settings	144
Using Pre-Generated Proxy Files Created Outside of Shake	148
Pre-Generating Your Own Proxies	150
Rendering Proxies on the Command Line	153
Pre-Generated Proxy File References in FileIn Nodes	154
Anamorphic Images and Pre-Generated Proxies	155
How Proxy Paths Are Defined	155
Proxies of YUV Files	156
Organizing Proxy Files	156
Full-Resolution Proxies and Network Rendering	157
Customizing the Format of Pre-Generated Proxies	158
Pre-Generating Proxies Outside of the User Interface	160
Using Pre-Generated Proxies in Your Script	161
Keeping High-Resolution Elements Offline	162
When Not to Use Proxies	163
Do Not Use Proxies for Tracking	163
Proxies and Z-Depth	163
Proxy Parameters	164
In the Globals Tab	164
Adding Your Own Entry to the proxySet Pop-Up Menu	165
FileIn	166
Compatible File Formats and Image Resolutions	167
File Formats	167
Shake Does Not Support HDV	167
Image Sequences	167
QuickTime Files	168
Image Formats That Support tTmp Files	168
Nodes That Create tmp Files	170
Table of Supported File Formats	170
Format Descriptions	173
IFF	173
CIN	173
DPX	174
OpenEXR	174
JPEG	177
MOV, AVI	177
PSD (Photoshop)	177
rgb, sgi, bw, raw, sgiraw	177
rla, rpf	177
yuv, qnt, qtl, pal	177
Support for Custom File Header Metadata	178
Table of File Sizes	180
Controlling Image Resolution	180
Combining Images of Differing Resolution	181
Changing Resolution	181
Nodes That Affect Image Resolution	183
Fit	183
Resize	184
Zoom	185
Remastering to a Different Resolution With Proxies	185
For more information on working with proxies and high-resolution images, see Chapter 3, “Adding M...	185
Cropping Functions	186
AddBorders	186
Crop	186
Viewport	187
Window	189
Importing Video and Anamorphic Film	191
The Basics of Processing Interlaced Video	191
Preserving, Eliminating, and Creating Interlacing	191
Understanding Video Interlacing	192
Common Issues When Compositing Interlaced Images	194
Setting Up Your Script to Use Interlaced Images	196
Setting the deInterlacing Parameter of Each FileIn Node	197
How to Determine Field Dominance	198
Setting the reTiming Parameters of Each FileIn Node	198
Displaying Individual Fields in the Viewer	200
Zooming In on Interlaced Images in the Viewer	202
Exporting Field Interlaced Footage	203
JPEGs and Fields	204
Integrating Interlaced and Non-Interlaced Footage	204
Video Functions	205
Interlace	205
DeInterlace	206
Field	207
SwapFields	207
VideoSafe	208
About Aspect Ratios and Nonsquare Pixels	209
What is Anamorphic Video?	209
Anamorphic Examples	210
Properly Viewing Squeezed Images	210
Node Aspect Ratio and the defaultAspect Parameter	211
Compositing Square Pixel Images With Squeezed Images	212
Inheritance of the defaultAspect Parameter for Individual Nodes	213
3D Software Renders	214
Tuning Parameters in Squeezed Space	214
Rendering Squeezed Images	215
Handling Video Elements	215
Preset Formats	216
Table of Common Aspect Ratios	216
Using the Node View	217
About Node-Based Compositing	217
Where Do Nodes Come From?	218
Navigating in the Node View	219
The Node View Overview	219
Favorite Views	220
Using the Enhanced Node View	221
Enhanced Node View Parameters	222
Noodle Display Options	224
Noodle Tension	225
Customizing Noodle Color Coding	225
Customizing Noodle Stippling	225
Creating Custom Stipple Patterns	226
Creating Nodes	226
Selecting and Deselecting Nodes	228
Connecting Nodes Together	231
One Input, Many Outputs	233
Breaking Node Connections	235
Inserting, Replacing, and Deleting Nodes	235
Inserting Nodes Into a Tree	236
Deleting and Disconnecting Nodes From a Tree	238
Copying and Pasting Nodes	239
Moving Nodes	240
Loading a Node Into a Viewer	240
Loading Node Parameters	241
Ignoring Nodes	243
Renaming Nodes	243
Name Nodes Carefully	244
Arranging Nodes	244
Grid Snap	244
Grid Parameters in the Globals Tab	244
Automatic Layout Arrangement	245
Groups and Clusters	246
Clusters	247
Group Parameters	249
Opening Macros	251
Cloning Nodes	251
Thumbnails	253
Customizing Thumbnail Display	253
Adding Thumbnails to Nodes	254
Updating Thumbnails	255
Toggling Thumbnails Between Color and Alpha Channels	256
Defining Which Nodes Are Created With Thumbnails	256
The Node View Shortcut Menu	257
Using the Time View	261
About the Time View	261
Viewing Nodes in the Time View	262
Clip Durations in the Time View	263
Adjusting Image Nodes in the Time View	263
Trimming and Looping QuickTime Clips and Still Images	263
Image Node Controls	264
Image Sequence Timing Controls	264
Customizing How the Last Frame Is Represented	268
Reversing a Clip	269
The Transition Node	270
Customizing the Transition Node	272
Create Your Own Transition Type	273
Using the Audio Panel	277
About Audio in Shake	277
Audio and QuickTime	277
Loading, Refreshing, and Removing Audio Files	278
Previewing and Looping Audio	280
Secondary Peak Meter	281
Muting and Soloing Tracks	282
Playing Audio With Your Footage	282
Viewing Audio	283
Slipping Audio Sync in Your Script	283
Time Shift Subparameters	284
Playback Rate Subparameters	285
Track Gain Subparameters	285
Extracting Curves From Sound Files	285
Create Curves Options	287
Exporting an Audio Mix	288
Mixdown Options	288
Parameter Animation and the Curve Editor	291
Animating Parameters With Keyframes	291
Animating Parameters Using Keyframes	291
Rules for Keyframing	293
Adding Blank and Duplicate Keyframes to Pause Animation	293
Navigating Among Keyframes in the Time Bar	294
Using the Curve Editor	294
Loading and Viewing Curves in the Editor	295
Controlling Curves Displayed in the Curve Editor	296
Navigating the Curve Editor	298
Curve Editor Right-Click Menus	298
The Curve Editor Buttons	299
Splitting the Curve Editor	300
Working With Keyframes	300
Adding Keyframes	300
Selecting Keyframes	302
Deleting Keyframes and Curves	303
Modifying Keyframes	303
Copying and Pasting Keyframes	314
Modifying Curves	315
The Right-Mouse Menu	316
More About Splines	316
The Flipbook, Monitor Previews, and Color Calibration	323
Cached Playback From the Viewer	323
Launching the Flipbook	323
Flipbook Controls	324
Viewing, Zooming, and Panning Controls	325
Memory Requirements	325
Customizing the Flipbook	326
Creating a Disk-Based Flipbook	326
Disk-Based Flipbook Temporary Files	329
Viewing on an External Monitor	330
Customizing External Monitor Output	330
Navigating the Broadcast Monitor	331
Monitor Calibration With Truelight	331
Rendering With the FileOut Node	333
Attaching FileOut Nodes Prior to Rendering	333
The FileOut Node	334
Rendering From the Command Line	336
Using the Render Parameters Window	337
The Render Menu	339
Support for Apple Qmaster	339
Image Caching	343
About Caching in Shake	343
Cache Parameters in the Globals Tab	343
Using the Cache Node	344
When the Cache Becomes Full	345
Caching and Updating Frames	346
Parameters in the Cache Node	347
Commands to Clear the Cache	349
Memory and the Cache in Detail	349
Limits to Shake RAM Usage	350
The Image Cache	350
Preservation of the Disk Cache	351
The Processing Cache	351
Customizing Image Caching Behavior	352
Customizing Shake	355
Setting Preferences and Customizing Shake	355
Creating and Saving .h Preference Files	355
Finding Shake’s Default Settings	356
Creating Your Own Preference Files	356
Possible Preference File Locations	357
Installing Custom Settings and Macros	357
Installing Custom Interface Settings	358
Installing Custom Icons	358
Preference File Load Order	358
Troubleshooting Preference Files	359
Customizing Interface Controls in Shake	359
Color Settings for Various Interface Items	359
Custom Stipple Patterns in the Enhanced Node View	365
Adding Custom Media Formats to the Format Menu	365
Setting Format Defaults	366
Assigning Default Width and Height to a Parameter in a Macro	366
Setting Maximum Viewer Resolution in the Interface	366
Default Timecode Modes and Displays	367
Autosave Settings	367
Undo Level Number	368
Amount of Processors to Assign to the Interface	368
Font Size for Menus and Pop-Up Menus	369
Adding Functions to the Right-Click Menu	369
Adding Functions Into a Menu	370
Opening Scripts With Missing Macros	370
Linking an HTML Help Page to a Custom Node	370
The Curve Editor and Time Bar	370
Customizing File Path and Browser Controls	371
Setting Default Browser Directories	371
Using the UNC File Name Convention	372
Using Relative Path Conventions	372
Adding Personal Favorites to the Browser	372
Assigning a Browser Pop-Up Menu to a Parameter	373
Automatic Launching of the Browser When Creating a Node	374
Automatic Browser File Filters	374
Tool Tabs	375
Setting the Number of Node Columns in a Tool Tab	375
Using the Alternative Icons	375
Attaching a Function to a Button in the Tabs	376
Attaching a Function to a Button Without an Icon	377
Creating Multiple Nodes With One Function	377
Light Hardware Mode	378
Customizing the Node View	378
Using Parameters Controls Within Macros	379
Assigning a Color Control	379
Assigning the Old Color Control	380
Changing Default Values	381
Grouping Parameters in a Subtree	382
Setting Slider Ranges	382
Adding Pop-Up Menus	383
Creating Radio Buttons	384
Creating Push-Button Toggles	384
Creating On/Off Buttons	385
Making a Parameter Non-Animateable	385
Placing a Curve Editor Into a Parameters Tab	386
Viewer Controls	386
Setting Maximum Viewer Resolution in the Interface	386
Onscreen Controls	387
Template Preference Files	392
Changing the Default QuickTime Configuration	392
Environment Variables for Shake	393
Creating the .plist Environment File	395
Using the .tcshrc Environment File	397
Shake Variables	398
To Test Your Environment Variable	399
Using Aliases	399
Interface Devices and Styles	400
Using a Stylus	400
Dual-Head Monitors	400
Customizing the Flipbook	401
Configuring Additional Support for Apple Qmaster	401
RenderQueue Options	401
Part II: Compositing With Shake	403
Image Processing Basics	405
About This Chapter	405
Taking Advantage of the Infinite Workspace	405
Clipped Images	407
Bit Depth	408
Comparing Different Bit Depths	408
Avoiding Color Banding	410
Float	411
Bit Depth Independence	411
The Bytes Node	413
Channels Explained	414
Combining Images With Different Channels	414
Viewing the Number of Image Channels	415
Displaying Individual Channels in the Viewer	415
Changing the Number of Image Channels	416
Compositing Basics and the Alpha Channel	417
Example 1: Compositing Using the Over Node	417
Example 2: Compositing Using the KeyMix Node	418
Example 3; Assigning an Alpha Channel With the SwitchMatte Node	419
Combining Images in Other Ways	420
Using the ClipMode Parameter of Layer Nodes	421
About Premultiplication and Compositing	421
In a Nutshell—the Rules of Premultiplication	422
Problems Caused When Premultiplication Is Ignored	422
The Math of Over and KeyMix	424
Unpremultiplying an Image	426
Remember This	431
Managing Premultiplication	431
Filters and Premultiplication	433
Remember This	433
Nodes That Affect Premultiplication	436
Non-Black Premultiplied Images	436
The Logarithmic Cineon File	437
A Little Further Reading	439
The Hazards of Color Correcting in Logarithmic Color	439
Converting Between Logarithmic and Linear Color	441
Wedging and Color Timing	442
Logarithmic Color and Float Bit Depth	444
Looking at Float Values	448
Float Bit Depth and Third-Party Plug-Ins	449
Compositing With Layer Nodes	451
Layering Node Essentials	451
Don’t Mask Layer Nodes	451
Remember the Rules of Premultiplication	451
Using the clipMode Parameter of Layer Nodes	452
Compositing Math Overview	452
The Layer Nodes	453
AddMix	453
AddText	456
Atop	457
Common	458
Constraint	459
Copy	460
IAdd	461
IDiv	461
IMult	462
Inside	462
Interlace	463
ISub	463
ISubA	463
KeyMix	464
LayerX	465
Max	465
Min	465
Mix	466
MultiLayer	466
Outside	466
Over	466
Screen	467
SwitchMatte	467
Under	468
Xor	468
ZCompose	469
Other Compositing Functions	470
AddShadow	470
DropShadow	470

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1,000
1,001
1,002
1,003
1,004
1,005
1,006
1,007
1,008
1,009
1,010
1,011
1,012
1,013
1,014
1,015
1,016
1,017
1,018
1,019
1,020
1,021
1,022
1,023
1,024
1,025
1,026
1,027
1,028
1,029
1,030
1,031
1,032
1,033
1,034
1,035
1,036
1,037
1,038
1,039
1,040
1,041
1,042
1,043
1,044
1,045
1,046
1,047
1,048
1,049
1,050
1,051
1,052
1,053
1,054

Match case Limit results 1 per page

436

Chapter 15

Image Processing Basics

Nodes That Affect Premultiplication

The following nodes can change the premultiplication status of an image, although

anything that operates an image’s mask differently from the RGB channels changes the

effect.

Node

Description

Color–

ColorCorrect

This color corrector has an option in its Misc tab to specify when

the incoming image is premultiplied. If it is, set the premultiplied

parameter to yes.

MDiv

and

MMult

are internally inserted into the

computation.

Color–

Reorder

This node allows you to switch a channel into the alpha channel,

and may disrupt your premultiplication status. However, it isn’t

often used on images in the normal chain of color correct, position,

and composite operations—but it is more of a utility node.

Filter–

DilateErode

This node is typically used to add to or chew the matte by a few

pixels. Set your channels to just “a.” Because you then modify the

matte separately from the RGB, you make the image

unpremultiplied.

Key–

LumaKey, DepthKey,

DepthSlice

These keyers all have the option to immediately set your image to

a premultiplied state.

Key–

KeyLight

This keyer can output either a premultiplied or an unpremultiplied

version, or just the alpha channel with the RGB untouched.

Key–

Primatte

This keyer can output either just the alpha or a premultiplied

version. Setting it to unpremultiplied requires an external

MDiv

Layer–

AddMix

This modified

Over

node allows you to manually break the

premultiplied relationship by tweaking curves that specify how the

matte multiplies the foreground and background images. It was

inherited from another package, where it was used extensively

because this particular system had no control over

premultiplication.

Layer–

SwitchMatte

This node copies a channel from the second image to the alpha

channel of the first image. You have the option to immediately

premultiply the image (enabled by default).

Other–

DropShadow

This node should be applied to premultiplied images only.

Non-Black Premultiplied Images

Some packages output images that are considered premultiplied, but in which the

background is not black. This is mathematically bizarre. To work with these images,

try the

AEPremult

macro included Chapter 32, “

he C

,” on page 989.