Fry wrote in this thread (http://processing.org/discourse/yabb_beta/YaBB.cgi?board=Syntax;action=display;num=1124271574):

"nope, alpha() is now mask() as of beta:
http://processing.org/reference/PImage_mask_.html
i'll add it to the faq on updating alpha -> beta code"


So it should be the same, but maybe there were some internal changes? do you have a quick example?

I'm pretty convinced that the results are different with mask than they were with alpha. I'm sure it's not my monitor as the two functions produce clearly different results.(see gifs linked below)

here's test code using BImage and alpha in v0069:
----------------
size(255,255);
background(255);
BImage pixelblack;
pixelblack = loadImage("pen0.gif");
imageMode(CENTER_DIAMETER);
int[] alphaVList = new int [1];

for(int i=0;i<255;i++){
 alphaVList[0] = i;
 pixelblack.alpha(alphaVList);
 image(pixelblack,150,i);
}
---------------------
this produces : http://www.atomless.com/images/v0069_alpha.gif

and here's test code using PImage and mask in v0091:
---------------------
size(255,255);
background(255);
PImage pixelblack;
pixelblack = loadImage("pen0.gif");
imageMode(CORNERS);
int[] alphaVList = new int [1];

for(int i=0;i<255;i++){
 alphaVList[0] = i;
 pixelblack.mask(alphaVList);
 pixelblack.updatePixels();
 image(pixelblack,150,i);
}
------------------------
this produces : http://www.atomless.com/images/v0091_mask.gif

Hi Ben,

I was originally using the centre_diameter image mode when using 0069 but had to change it when porting to 0091 beta. I just tried to recreate a couple of test programs that matched the code I'm using in the full programs.

Using the P3D renderer makes no difference. Must be changes in the renderers since 0069 I guess. To my eyes the gradient possible with the old alpha function is smoother, more gradual and seems more evenly spread.

I feel I'm nit picking to a certain extent but it does seem more difficult to achieve the pleasing smooth gradients with mask that I was able to achieve with alpha.

actually, as this code illustrates :

------------------
size(255,255);
background(255);
PImage pixelblack;
pixelblack = loadImage("pen0.gif");
imageMode(CORNERS);
int[] alphaVList = new int [1];

for(int i=0;i<255;i++){
 alphaVList[0] = i;
 pixelblack.mask(alphaVList);
 pixelblack.updatePixels();
 for(int j=0;j<50;j++){
   image(pixelblack,150+j,i);
   color c = color(255-i, 255-i, 255-i);
   set(205+j,i, c);
 }
 
}
-------------------------

when you lay out all of the greyscale values between 0 and 255 end to end from top to bottom alongside the mask gradient the two are identicle.

The mask function does give different results to that of the old alpha function but as the mask gradient matches a uniform gradient between greyscale 0 and 255 then maybe it's  an improvement on the alpha function which does not match the uniform grayscale gradient.

I still prefer the resulting aesthetic I was getting in my programs with the alpha gradient but I'm sure I can tweak things to recapture this. I would, however, be intrigued to know what caused the change as it's the same both with the JAVA2D renderer and the P3D renderer.

now filed in the bugs db:
http://dev.processing.org/bugs/show_bug.cgi?id=148