diff --git a/library/src/main/ets/downsampling/Downsampler.ets b/library/src/main/ets/downsampling/Downsampler.ets
index a94000f..517fc34 100644
--- a/library/src/main/ets/downsampling/Downsampler.ets
+++ b/library/src/main/ets/downsampling/Downsampler.ets
@@ -27,9 +27,10 @@ export interface calculateScaleType {
   targetHeight: number
 }
 
+
 export class Downsampler {
   calculateScaling(
-    typeValue: string,
+    typeValue: string |null,
     sourceWidth: number, //原始宽高
     sourceHeight: number, //原始宽高
     requestWidth: number, //请求宽高
@@ -38,7 +39,7 @@ export class Downsampler {
   ): calculateScaleType {
 
     if (sourceHeight <= 0 || sourceWidth <= 0) {
-        throw new Error("非法宽高 sourceHeight sourceWidth")
+        throw new Error(`Invalid width and height, sourceHeight:${sourceHeight}+ sourceWidth:${sourceWidth}`)
     }
     let downsampler = this.getDownsampler(downsampType);
     let exactScaleFactor: number =
@@ -46,7 +47,7 @@ export class Downsampler {
     let rounding: SampleSizeRounding =
       downsampler.getSampleSizeRounding(sourceWidth, sourceHeight, requestWidth, requestHeight, downsampType); //采样类型
     //原始宽高和缩放系数的乘积
-    let outSize = {
+    let outSize:Size = {
       width: this.round(exactScaleFactor * sourceWidth),
       height: this.round(exactScaleFactor * sourceHeight)
     }
@@ -64,11 +65,16 @@ export class Downsampler {
         targetHeight: Math.floor(sourceHeight / scaleFactor)
       }
     } else if (typeValue === "webp") {
-      targetWidth = Math.round(sourceWidth / scaleFactor);
-      targetHeight = Math.round(sourceHeight / scaleFactor);
+      return {
+        targetWidth: Math.round(sourceWidth / scaleFactor),
+        targetHeight: Math.round(sourceHeight / scaleFactor)
+      }
     } else {
-      targetWidth = sourceWidth / scaleFactor;
-      targetHeight = sourceHeight / scaleFactor;
+      return {
+        targetWidth: sourceWidth / scaleFactor,
+        targetHeight: sourceHeight / scaleFactor
+
+      }
     }
   }