Reduce allocations during readNativeFrames with frame channel

Author: segmed-lam

read.go

@@ -256,9 +256,9 @@ func (r *reader) readPixelData(vl uint32, d *Dataset, fc chan<- *frame.Frame) (V
 
 			if fc != nil {
 				fc <- &f
+			} else {
+				image.Frames = append(image.Frames, &f)
 			}
-
-			image.Frames = append(image.Frames, &f)
 		}
 		image.IntentionallySkipped = r.opts.skipPixelData
 		return &pixelDataValue{PixelDataInfo: image}, nil
@@ -440,18 +440,23 @@ func (r *reader) readNativeFrames(parsedData *Dataset, fc chan<- *frame.Frame, v
 	image.Frames = make([]*frame.Frame, nFrames)
 	bo := r.rawReader.ByteOrder()
 	pixelBuf := make([]byte, bytesAllocated)
+	nativeDataBuf := make([][]int, pixelsPerFrame)
+	buf := make([]int, pixelsPerFrame*samplesPerPixel)
 	for frameIdx := 0; frameIdx < nFrames; frameIdx++ {
+		if fc == nil {
+			nativeDataBuf = make([][]int, pixelsPerFrame)
+			buf = make([]int, pixelsPerFrame*samplesPerPixel)
+		}
 		// Init current frame
 		currentFrame := frame.Frame{
 			Encapsulated: false,
 			NativeData: frame.NativeFrame{
 				BitsPerSample: bitsAllocated,
 				Rows:          MustGetInts(rows.Value)[0],
 				Cols:          MustGetInts(cols.Value)[0],
-				Data:          make([][]int, pixelsPerFrame),
+				Data:          nativeDataBuf,
 			},
 		}
-		buf := make([]int, pixelsPerFrame*samplesPerPixel)
 		if bitsAllocated == 1 {
 			if err := fillBufferSingleBitAllocated(buf, r.rawReader, bo); err != nil {
 				return nil, bytesToRead, err
@@ -482,9 +487,10 @@ func (r *reader) readNativeFrames(parsedData *Dataset, fc chan<- *frame.Frame, v
 				currentFrame.NativeData.Data[pixel] = buf[pixel*samplesPerPixel : (pixel+1)*samplesPerPixel]
 			}
 		}
-		image.Frames[frameIdx] = &currentFrame
 		if fc != nil {
 			fc <- &currentFrame // write the current frame to the frame channel
+		} else {
+			image.Frames[frameIdx] = &currentFrame
 		}
 	}
 	if skipFinalPaddingByte {