c# - Translate/Detect Rectangle portion of Image from Resized Image -

i have large size image.since takes long process high res images resize keeping aspect ratio.from resized image detect rectangle , have coordinates of rectangle.

 bitmap resizekeepaspectratio(bitmap imgphoto, int width, int height)         {             int sourcewidth = imgphoto.width;             int sourceheight = imgphoto.height;             int sourcex = 0;             int sourcey = 0;             int destx = 0;             int desty = 0;              float npercent = 0;             float npercentw = 0;             float npercenth = 0;              npercentw = ((float)width / (float)sourcewidth);             npercenth = ((float)height / (float)sourceheight);             if (npercenth < npercentw)             {                 npercent = npercenth;                 destx = system.convert.toint16((width -                               (sourcewidth * npercent)) / 2);             }             else             {                 npercent = npercentw;                 desty = system.convert.toint16((height -                               (sourceheight * npercent)) / 2);             }              int destwidth = (int)(sourcewidth * npercent);             int destheight = (int)(sourceheight * npercent);              bitmap bmphoto = new bitmap(width, height,                               pixelformat.format24bpprgb);             bmphoto.setresolution(imgphoto.horizontalresolution,                              imgphoto.verticalresolution);              graphics grphoto = graphics.fromimage(bmphoto);             grphoto.clear(color.red);             grphoto.interpolationmode =                     interpolationmode.highqualitybicubic;              grphoto.drawimage(imgphoto,                 new rectangle(destx, desty, destwidth, destheight),                 new rectangle(sourcex, sourcey, sourcewidth, sourceheight),                 graphicsunit.pixel);              grphoto.dispose();             return bmphoto;         } 

is there way can translate/map rectangle large image same area.im doing save time.

some clarification: have large original image.. resize keeping aspect ratio , using processing rectangle portion in it( coordinates).since image quality of portion not need find way map coordinate large image.

ok, if understand clear here is:

you have viewport in select rectangle , want scale rectangle unscaled image.

so have function this:

public rectanglef translatescale(rectanglef croprectangle, bitmap imgphoto) 

first of need calculate multiplier fit image on viewport, function:

        int sourcewidth = imgphoto.width;         int sourceheight = imgphoto.height;         int sourcex = 0;         int sourcey = 0;         int destx = 0;         int desty = 0;          float npercent = 0;         float npercentw = 0;         float npercenth = 0;          npercentw = ((float)width / (float)sourcewidth);         npercenth = ((float)height / (float)sourceheight);         if (npercenth < npercentw)             npercent = npercenth;         else             npercent = npercentw; 

now know scale percentage take inverse of function, instead of multiply divide rectangle size , position:

        croprectangle.x /= npercent;         croprectangle.y /= npercent;         croprectangle.width /= npercent;         croprectangle.height /= npercent          return croprectangle; 

and that's it, have rectangle scaled original image size, can crop rectangle.