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How does the value of alpha channel affect the video ?

April 4, 2008 | 4:03 pm

I feel confused about alpha channel and the way jit.alphablend works.

I tried to make a patch to see if the value of alpha channel really affects the video, but it does not seem to change anything.

My way of doing it is to multiply alpha channel value with jit.op. I found that whatever the multiplier value is, the resulted video is the same. Does this mean that changing the alpha channel value does not affect the resulted video ?

Could anyone explain it ? Thanks.

The following is the testing patch I made:

max v2;
#N vpatcher 74 59 1195 848;
#P user jit.cellblock 38 546 225 761 3 9 320 240 45 17 0 1 1 0 0 0 1 1 1 0 0 0 255 255 255 0 0 0 0 0 0 191 191 191 0 0 0 215 215 240 1 1 1 0 4 0 0 0;
#P user jit.cellblock 41 313 228 528 3 9 320 240 45 17 0 1 1 0 0 0 1 1 1 0 0 0 255 255 255 0 0 0 0 0 0 191 191 191 0 0 0 215 215 240 1 1 1 0 4 0 0 0;
#P user jit.pwindow 415 397 151 170 0 1 0 0 1 0;
#P toggle 514 109 15 0;
#P window setfont "Sans Serif" 9.;
#P window linecount 1;
#P newex 511 148 52 196617 metro 30;
#P message 573 152 76 196617 read bball.mov;
#P newex 547 206 63 196617 jit.qt.movie;
#P newex 416 346 64 196617 jit.op @op +;
#P user jit.pwindow 244 452 151 170 0 1 0 0 1 0;
#P newex 248 285 53 196617 jit.pack;
#P flonum 99 171 35 9 0 0 0 3 0 0 0 221 221 221 222 222 222 0 0 0;
#P message 100 192 39 196617 val $1;
#P newex 139 254 65 196617 jit.op @op *;
#P newex 245 228 66 196617 jit.unpack;
#P toggle 212 102 15 0;
#P newex 209 132 52 196617 metro 30;
#P message 271 145 30 196617 open;
#P newex 245 199 56 196617 jit.qt.grab;
#P connect 4 0 17 0;
#P connect 5 0 16 0;
#P connect 7 0 6 0;
#P connect 4 0 5 0;
#P connect 2 0 5 0;
#P connect 6 0 5 1;
#P connect 3 0 2 0;
#P connect 2 0 0 0;
#P connect 1 0 0 0;
#P connect 0 0 4 0;
#P connect 8 0 9 0;
#P connect 5 0 8 0;
#P connect 4 1 8 1;
#P connect 4 2 8 2;
#P connect 4 3 8 3;
#P connect 8 0 10 0;
#P connect 10 0 15 0;
#P connect 11 0 10 1;
#P connect 14 0 13 0;
#P connect 12 0 11 0;
#P connect 13 0 11 0;
#P pop;


April 4, 2008 | 4:30 pm

I think it only makes a difference if there an element in the background, such as another video or perhaps an image. Alpha channel shouldn’t affect just a single video or a single image, bcs there is nothing to see behind it. Maybe I am wrong.


April 4, 2008 | 8:32 pm

try this, and see if you still have questions…

#P window setfont "Sans Serif" 9.;
#P window linecount 1;
#P newex 291 375 70 196617 jit.alphablend;
#P user jit.cellblock 41 313 228 528 3 9 320 240 45 17 0 1 1 0 0 0 1 1 1 0 0 0 255 255 255 0 0 0 0 0 0 191 191 191 0 0 0 215 215 240 1 1 1 0 4 0 0 0;
#P message 546 143 83 196617 read dishes.mov;
#P newex 547 206 63 196617 jit.qt.movie;
#P user jit.pwindow 291 404 151 170 0 1 0 0 1 0;
#P newex 248 285 53 196617 jit.pack;
#P flonum 99 171 35 9 0 0 0 3 0 0 0 221 221 221 222 222 222 0 0 0;
#P message 100 192 39 196617 val $1;
#P newex 193 257 65 196617 jit.op @op *;
#P newex 245 228 66 196617 jit.unpack;
#P toggle 212 102 15 0;
#P newex 209 132 52 196617 metro 30;
#P message 270 136 30 196617 open;
#P newex 245 199 56 196617 jit.qt.grab;
#P connect 2 0 0 0;
#P connect 2 0 10 0;
#P connect 10 0 13 1;
#P connect 8 0 13 0;
#P connect 13 0 9 0;
#P connect 11 0 10 0;
#P connect 4 3 8 3;
#P connect 4 2 8 2;
#P connect 4 1 8 1;
#P connect 5 0 12 0;
#P connect 5 0 8 0;
#P connect 0 0 4 0;
#P connect 1 0 0 0;
#P connect 3 0 2 0;
#P connect 6 0 5 1;
#P connect 4 0 5 0;
#P connect 7 0 6 0;
#P window clipboard copycount 14;


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