Hi, this might help: http://objectpainters.com/blog/2007/11/30/inverting-the-alpha-of-a-bitmap-image/
It does not half but invert the alpha, but the principle is the same I think. The problem lies in the premultiplication of the alpha. greetz JC On Tue, Oct 7, 2008 at 4:48 AM, Juan Pablo Califano <[EMAIL PROTECTED]> wrote: > PD: > > Sorry, even though the result is the same, to make more sense the second > sample should read: > > > var hexaValue:int = 0x9100ff33; > var a:int = (hexaValue >> 24) & 0xff; > var rgb:int = hexaValue & 0xffffff; > > var newAlpha:int = 0xcc; > copyHexaValue = newAlpha << 24 | rgb; > trace(uint(copyHexaValue).toString(16)); // traces cc00ff33 > Using rgb as the name of the var that stores the value of the RGB > components, instead of arg. > > > 2008/10/6, Juan Pablo Califano <[EMAIL PROTECTED]>: >> >> Hi, >> >> If I haven't misread something, this >> >> a = a >> 1; >> >> makes no sense. Unless you're trying to divide alpha by 2, in which case I >> obviously missed something. >> >> >> If you want to extract the 4 components, you can use something like this: >> >> >> var hexaValue:int = 0x9100ff33; >> >> var a:int = (hexaValue >> 24) & 0xff; >> var r:int = (hexaValue >> 16) & 0xff;; >> var g:int = (hexaValue >> 8) & 0xff;; >> var b:int = hexaValue & 0xff; >> >> var newAlpha:int = 0xcc; >> var copyHexaValue:int = newAlpha << 24 | r << 16 | g << 8 | b; >> trace(uint(copyHexaValue).toString(16)); // traces cc00ff33 >> >> If you don't bother to get the individual RGB components, just the alpha >> channel, try this: >> >> var hexaValue:int = 0x9100ff33; >> var a:int = (hexaValue >> 24) & 0xff; >> var arg:int = hexaValue & 0xffffff; >> >> var newAlpha:int = 0xcc; >> copyHexaValue = newAlpha << 24 | arg; >> trace(uint(copyHexaValue).toString(16)); // traces cc00ff33 >> Also, I'm casting to uint just to display the value in a more >> meaningful/readable way in the trace, but as long as you don't perform >> arithmetic on those values, you don't have to (because it's parsed as a bit >> pattern, not as numerical value, if that makes sense...). >> >> Cheers >> Juan Pablo Califano >> >> >> 2008/10/6, sebastian <[EMAIL PROTECTED]>: >>> >>> hi Glen, >>> >>> Kudos for the shift >> 1 operation, knew that was a faster operand. >>> >>> However, this code is still now working, now it simply doesn't change >>> anything... >>> :( >>> >>> var val:uint = getPixel32(x,y); >>> var a:uint = (val >> 24) & 0xff; >>> var rgb:uint = val & 0xffffff; >>> a = a >> 1; >>> var newval:uint = (a << 32) | rgb; >>> setPixel32(x,y,newval); >>> >>> I also tried changing it to say: >>> >>> ... >>> var rgb:uint = val & 0x00ffffff; >>> a = a >> 1; >>> var newval:uint = (a << 24) | rgb; >>> ... >>> >>> since I thought that was an error maybe, but that also doesn't influence >>> the alpha of the pixel... >>> :( >>> >>> Out of desperation I also tried: >>> >>> var a:uint = val & 0xff000000; >>> var rgb:uint = val & 0x00fffff; >>> a = a >> 1; >>> var newval:uint = a | rgb; >>> >>> and >>> >>> var a:uint = val & 0xff000000; >>> var rgb:uint = val & 0x00fffff; >>> a = a >> 1; >>> var newval:uint = (a << 24) | rgb; >>> >>> :( >>> >>> sniff... >>> >>> Setting alpha for the whole MC is not an option for what I am doing. I'm >>> trying to create trails behind things that are moving by having a video-burn >>> like effect; by operating on the pixel level. At the moment I am using code >>> from 'Adventures in AS', but once i have it working I'll encapsulate it and >>> use it in a different project. >>> >>> The original source is: >>> >>> http://flashcoding.blogspot.com/2008/03/small-starfield-with-bluring-effect.html >>> >>> And my current draft-code modification is: >>> >>> package >>> { >>> import flash.events.*; >>> import flash.display.*; >>> import flash.display.Bitmap; >>> import flash.display.BitmapData; >>> import flash.geom.Rectangle; >>> >>> >>> public class Starfield >>> { >>> var mc:MovieClip =new MovieClip(); >>> var screendata:BitmapData; >>> >>> var stars:Array=new Array(); >>> var antal:Number=500; >>> >>> public function Starfield(timeline) >>> { >>> >>> screendata=new >>> BitmapData(320,240,false,0x00000000); >>> var screen:Bitmap=new Bitmap(screendata); >>> mc.addChild(screen); >>> >>> for (var i:int=0;i<antal;i++) >>> { >>> InitStar(i); >>> } >>> >>> mc.addEventListener(Event.ENTER_FRAME,this.render); >>> timeline.addChild(mc); >>> } >>> >>> private function MoveStar(index:int) >>> { >>> if (stars[index][0]<-160 || stars[index][0]>160 || >>> stars[index][1]<-120 || stars[index][1]>120) >>> { >>> InitStar(index); >>> } >>> else >>> { >>> stars[index][0]= >>> stars[index][0]*stars[index][2]; >>> stars[index][1]= >>> stars[index][1]*stars[index][2]; >>> } >>> } >>> >>> private function InitStar(index:int) >>> { >>> >>> stars[index]=[Number(((Math.random()*10)-5)),Number(((Math.random()*10)-5)),Number((Math.random()/10)+1)]; >>> } >>> >>> >>> private function render(e:Event):void >>> { >>> for(var x:int=0;x<320;x++) >>> { >>> for(var y:int=0;y<240;y++) >>> { >>> >>> var val:uint = >>> screendata.getPixel32 (x,y); >>> >>> var a:uint = (val >> 24) & 0xff; >>> var rgb:uint = val & 0xffffff; >>> a = a >> 1; >>> var newval:uint = (a << 24) | rgb; >>> >>> screendata.setPixel32(x,y,newval); >>> >>> } >>> } >>> >>> for(var i:int=0;i<antal;i++) >>> { >>> MoveStar(i); >>> >>> screendata.setPixel(stars[i][0]+160,stars[i][1]+120,0xFFFFFF); >>> } >>> } >>> } >>> } >>> >>> >>> Regards, >>> >>> Sebastian. >>> >>> >>> Glen Pike wrote: >>> >>>> Hi, >>>> >>>> I think you need to shift by 24 for alpha, you also need to shift then >>>> mask the value. RGB is just the bottom three bytes masked and shifting by >>>> 1 >>>> rather than divide by 2 may be faster, but google for the speed comparisons >>>> in AS3 - I think John Grden may have blogged this: >>>> var a:uint = (val >> 24) & 0xff; >>>> var rgb:uint = val & 0xffffff; >>>> a = a >> 1; >>>> var newval:uint = (a << 32) | rgb; >>>> >>>> It would be a good learning exercise to do your own equations for >>>> manipulating pixel stuff, but have a look at Mario Klingemann's blog - >>>> quasimondo.com - for tips and tricks with images as he is one of the >>>> best people at manipulating bitmaps in Flash so he may have some nice >>>> examples to stimulate you. For simpler manipulation have a google. Also, >>>> if you are just setting the alpha to 50% for the whole bitmap, it may be >>>> quicker to do this on the MovieClip because FlashPlayer might be optimising >>>> composition somehow, but I understand this may just be an example. >>>> >>>> HTH >>>> >>>> Glen >>>> sebastian wrote: >>>> >>>>> Thanks Glen and Andrew, >>>>> >>>>> Thanks for your fast help, >>>>> >>>>> Tried to use this code [below] but it makes my pixels yellow instead of >>>>> 50% alpha on each pass... any ideas why? >>>>> >>>>> Is there any good tutorial on working with bit operations and bit logic? >>>>> Would make it easier for me to trouble shoot/make my own equations. >>>>> :) >>>>> >>>>> Thanks! >>>>> >>>>> Seb. >>>>> >>>>> Andrew Murphy wrote: >>>>> >>>>>> I'm not sure of this, but: After you grab "val" you could bitshift out >>>>>> the >>>>>> alpha channel ("a"), subtract that from the original argb value to >>>>>> remove >>>>>> the alpha channel. Manipulate "a" and bitshift it back up again before >>>>>> adding it to the rgb value to give you a new argb. >>>>>> >>>>>> >>>>>> var a:uint = val >> 32 & 0xff; >>>>>> var rgb:uint = val - (a << 32); >>>>>> a = a / 2; >>>>>> var newval:uint = rgb + (a << 32); >>>>>> >>>>>> >>>>>> >>>>>> -------------------------------- >>>>>> Andrew Murphy >>>>>> Interactive Media Specialist >>>>>> [EMAIL PROTECTED] >>>>>> >>>>>> Delvinia >>>>>> 214 King Street West, Suite 214 Toronto Canada M5H 3S6 >>>>>> >>>>>> P 416.364.1455 ext. 232 F 416.364.9830 W www.delvinia.com >>>>>> >>>>>> CONFIDENTIALITY NOTICE >>>>>> This email message may contain privileged or confidential information. >>>>>> If >>>>>> you are not the intended recipient or received this communication by >>>>>> error, >>>>>> please notify the sender and delete the message without copying or >>>>>> disclosing it. >>>>>> >>>>>> AVIS DE CONFIDENTIALITÉ >>>>>> Ce message peut contenir de l'information légalement privilégiée ou >>>>>> confidentielle. Si vous n'êtes pas le destinataire ou croyez avoir reçu >>>>>> par >>>>>> erreur ce message, nous vous saurions gré d'en aviser l'émetteur et >>>>>> d'en >>>>>> détruire le contenu sans le communiquer a d'autres ou le reproduire. >>>>>> >>>>>> >>>>>> >>>>>>> -----Original Message----- >>>>>>> From: [EMAIL PROTECTED] [mailto: >>>>>>> [EMAIL PROTECTED] On Behalf Of sebastian >>>>>>> Sent: Monday, October 06, 2008 3:18 PM >>>>>>> To: Flash Coders List >>>>>>> Subject: [Flashcoders] working with getPixel32 and setPixel32, >>>>>>> >>>>>>> hi folks, >>>>>>> >>>>>>> can any one shed some light to me on the setpixel32 and getpixel32? >>>>>>> >>>>>>> I'd like to be able to affect just one of the 4 components: A R G or B >>>>>>> independently of another. >>>>>>> >>>>>>> Essentially, read the current ARGB using getPixel32 and then >>>>>>> manipulate just one part of it, in my case, halve the current "A" value >>>>>>> of >>>>>>> the ARGB and then re-assign it back to the bitmap. >>>>>>> >>>>>>> >>>>>>> //1: grab the HEX value for the current coordinate: >>>>>>> var val:uint = getPixel32(x,y); >>>>>>> >>>>>>> //2: manipulate the HEX value of just 1 of the 4 parts, in my case the >>>>>>> A of the ARGB: >>>>>>> ???? >>>>>>> >>>>>>> //3: re-assign it back to the display: >>>>>>> setPixel32(x,y,val); >>>>>>> >>>>>>> Thanks for your help! >>>>>>> >>>>>>> Sebastian. >>>>>>> _______________________________________________ >>>>>>> Flashcoders mailing list >>>>>>> Flashcoders@chattyfig.figleaf.com >>>>>>> http://chattyfig.figleaf.com/mailman/listinfo/flashcoders >>>>>>> >>>>>> >>>>>> >>>>>> _______________________________________________ >>>>>> Flashcoders mailing list >>>>>> Flashcoders@chattyfig.figleaf.com >>>>>> http://chattyfig.figleaf.com/mailman/listinfo/flashcoders >>>>>> >>>>>> _______________________________________________ >>>>> Flashcoders mailing list >>>>> Flashcoders@chattyfig.figleaf.com >>>>> http://chattyfig.figleaf.com/mailman/listinfo/flashcoders >>>>> >>>>> >>>>> >>>> _______________________________________________ >>> Flashcoders mailing list >>> Flashcoders@chattyfig.figleaf.com >>> http://chattyfig.figleaf.com/mailman/listinfo/flashcoders >>> >> >> > _______________________________________________ > Flashcoders mailing list > Flashcoders@chattyfig.figleaf.com > http://chattyfig.figleaf.com/mailman/listinfo/flashcoders > _______________________________________________ Flashcoders mailing list Flashcoders@chattyfig.figleaf.com http://chattyfig.figleaf.com/mailman/listinfo/flashcoders
