c# - Easy way to get and set pixels on writeablebitmap -

i need , set pixel in universal app (windows phone rt, windows 8.1). , cannot find way. when in wpf first calculate stride like:

int stride = wb.pixelwidth * (wb.format.bitsperpixel / 8); 

after converting byte array

byte[] data = new byte[stride * wb.pixelheight]; wb.copypixels(data, stride, 0); 

and after easy:

for (int y = 0; y < wb.pixelheight; ++y) {     (int x = 0; x < wb.pixelwidth; ++x)     {         var index = (y * stride) + (x * 4);         data[index + 3]=255;         data[index + 2]=255          data[index + 1]=255          data[index]=255      } } 

but when use universal app cannot find way similar. cannot use savejpeg because work in silverlight, dont have writeablebitmap.format etc.

please help, suggestion welcome. thanx