Asp.net changes the image size when uploading images.

Unless you change the image format, try the following/*** /// <summary> /// to generate a thumbnail /// </Summary> /// <Param name = "originalimagepath"> source image path (physical path) </param> /// <Param name = "thumbnailpath"> thumbnail path (physical path) </param> /// <Param name = "width"> thumbnail width </param> /// <Param name = "height"> thumbnail height </param> // /<Param name = "Mode"> Create a thumbnail </param> Public static void makethumbnail (string originalimagepath, string thumbnailpath, int width, int height, string mode) {system. drawing. image originalimage = system. drawing. image. fromfile (originalimagepath); int towidth = width; int toheight = height; int x = 0; int y = 0; int ow = originalimage. width; int Oh = originalimage. height; Switch (mode) {Case "HW": // specify the height/width Scaling (may be deformed) break; Case "W": // specify the width, high toheight = originalimage. height * width/originalimage. width; break; Case "H": // specify the height. The width is proportional to towidth = originalimage. width * Height/originalimage. height; break; Case "cut": // specify the height and width (not deformed) if (double) originalimage. width/(double) originalimage. height> (double) towidth/(double) toheight) {Oh = originalimage. height; ow = originalimage. height * towidth/toheight; y = 0; X = (originalimage. width-ow)/2;} else {ow = originalimage. width; Oh = originalimage. width * Height/towidth; X = 0; y = (originalimage. height-OH)/2;} break; default: break;} // create a new BMP image system. drawing. image bitmap = new system. drawing. bitmap (towidth, toheight); // create a canvas system. drawing. graphics G = system. drawing. graphics. fromimage (Bitmap); // set the high quality interpolation method G. interpolationmode = system. drawing. drawing2d. interpolationmode. high; // set high quality, low speed rendering smoothness G. smoothingmode = system. drawing. drawing2d. smoothingmode. highquality; // clear the canvas and fill g with a transparent background color. clear (system. drawing. color. transparent); // specify the position and size of the original image. drawimage (originalimage, new system. drawing. rectangle (0, 0, towidth, toheight), new system. drawing. rectangle (X, Y, ow, oh), system. drawing. graphicsunit. pixel); try {// Save the thumbnail bitmap in JPG format. save (thumbnailpath, system. drawing. imaging. imageformat. JPEG);} catch (system. exception e) {Throw E;} finally {originalimage. dispose (); bitmap. dispose (); G. dispose ();}}