efficient cropping calculation in processing -

i loading png in processing. png has lot of unused pixels around actual image. luckily pixels transparent. goal crop png show image , rid of unused pixels. first step calculate bounds of image. wanted check every pixel alpha value , see if pixel highest or lowest coordinate bounds. this:

------ ------ --->oo oooooo oooooo 

then realized needed until first non-alpha pixel , repeat backwards highest coordinate bound. this:

------ -->ooo oooooo ooo<-- ------ 

this mean less calculating same result. code got out of still seems complex. here is:

class rect {  //class storing boundries   int xmin, xmax, ymin, ymax;   rect() {    } }  pimage gfx;  void setup() {   size(800, 600);   gfx = loadimage("resources/test.png");   rect _bounds = calcbounds();  //first calculate boundries   cropimage(_bounds);  //then crop image using boundries }  void draw() {  }  rect calcbounds() {   rect _bounds = new rect();   boolean _coordfound = false;   gfx.loadpixels();    //x min bounds   (int = 0; < gfx.width; i++) {  //rows     (int i2 = 0; i2 < gfx.height; i2++) {  //columns       if (alpha(gfx.pixels[(gfx.width * i2) + i]) != 0) {         _bounds.xmin = i;         _coordfound = true;         break;       }     }     if (_coordfound) {        break;     }   }    //x max bounds   _coordfound = false;   (int = gfx.width - 1; >= 0; i--) {  //rows     (int i2 = gfx.height - 1; i2 >= 0; i2--) {  //columns       if (alpha(gfx.pixels[(gfx.width * i2) + i]) != 0) {         _bounds.xmax = i;         _coordfound = true;         break;       }     }     if (_coordfound) {        break;     }   }    //y min bounds   _coordfound = false;   (int = 0; < gfx.height; i++) {  //columns     (int i2 = 0; i2 < gfx.width; i2++) {  //rows       if (alpha(gfx.pixels[(gfx.width * i) + i2]) != 0) {         _bounds.ymin = i;         _coordfound = true;         break;       }     }     if (_coordfound) {        break;     }   }    //y max bounds   _coordfound = false;   (int = gfx.height - 1; >= 0; i--) {  //columns     (int i2 = gfx.width -1; i2 >= 0; i2--) {  //rows       if (alpha(gfx.pixels[(gfx.width * i) + i2]) != 0) {         _bounds.ymax = i;         _coordfound = true;         break;       }     }     if (_coordfound) {        break;     }   }    return _bounds; }  void cropimage(rect _bounds) {   pimage _temp = createimage((_bounds.xmax - _bounds.xmin) + 1, (_bounds.ymax - _bounds.ymin) + 1, argb);   _temp.copy(gfx, _bounds.xmin, _bounds.ymin, (_bounds.xmax - _bounds.xmin) + 1, (_bounds.ymax - _bounds.ymin)+ 1, 0, 0, _temp.width, _temp.height);   gfx = _temp;  //now image cropped } 

isnt there more efficient/faster way calculate bounds of image? , still want boundries coordinates afterward instead of cutting away @ image during calculation.

if store last empty line found e.g. horizontal minimum , maximum scan in variable, can use constrain vertical scanning area has not yet been checked being empty, instead of having scan full columns. depending on amount , shape of croppable area can save quite bit - see schematic visual explanation of modified algorithm:

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by way, in //x min bounds scan seem iterating on width in both for loops, should height in 1 though? (unless images square of course :))