3647×2086，2.44M的jpg文件，我在Canvas 2d中用1920×1098绘制，wx.canvasToTempFilePath保存后，文件大小变成了4.087M，更换手机型号，大小有小量的变化。代码如下：

var canvas = param._this.data.imgCavObj;

            canvas.width = param.size.canvas_w * param._this.data.dpr;

            canvas.height = param.size.canvas_h * param._this.data.dpr;

            var ctx = param._this.data.imgCtx;

            ctx.scale(param._this.data.dpr, param._this.data.dpr);

            ctx.clearRect(0, 0, param.size.canvas_w, param.size.canvas_h);

            var img = param._this.data.cavImg;

            img.src = param.imgpath;

            img.onload = () => {

              ctx.drawImage(img, 0, 0, param.size.canvas_w, param.size.canvas_h);

              wx.canvasToTempFilePath({

                destWidth: param.size.canvas_w,

                destHeight: param.size.canvas_h,

                canvas: canvas,

                fileType: "jpg",

                quality: 0.3,

                success: function (res) {

                  if (param.success) param.success(res);

                },

                fail: function (res) {

                  if (param.fail) param.fail(res);

                }

              }, param._this);

            }

我想要的是文件大小变小，结果变大了。改变quality，文件大小也没有变化。