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BitmapFactory.Options inSampleSize の性能テストとか動作とか

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以下のような事が書いてありますが…

public int inSampleSize

Since: API Level 1
If set to a value > 1, requests the decoder to subsample the original image, returning a smaller image to save memory. The sample size is the number of pixels in either dimension that correspond to a single pixel in the decoded bitmap. For example, inSampleSize == 4 returns an image that is 1/4 the width/height of the original, and 1/16 the number of pixels. Any value <= 1 is treated the same as 1. Note: the decoder will try to fulfill this request, but the resulting bitmap may have different dimensions that precisely what has been requested. Also, powers of 2 are often faster/easier for the decoder to honor.

検証用ソース

1/1から、1/36の設定までを10回ずつループ。
出力された画像の幅と、処理時間の平均を出力。

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Resources res = getResources();
BitmapFactory.Options options = new BitmapFactory.Options();
 
int sizeMax = 36;
int count = 10;
 
long[][] result = new long[sizeMax][count];
long start;
 
for (int i = 1; i <= sizeMax; i++) {
	for(int j = 0; j < count; j++) {
		options.inSampleSize = i;
		start = System.currentTimeMillis();
		BitmapFactory.decodeResource(res, R.drawable.image, options);
		result[i-1][j] = System.currentTimeMillis() - start;
	}
	Log.d("width" + i, String.valueOf(options.outWidth));
}
 
double sec;
 
for (int i = 0; i < sizeMax; i++) {
	sec = 0;
	for (int j = 0; j < count; j++) {
		sec += result[i][j];
	}
	Log.d("avg:" + (i+1), String.valueOf(sec/count));
}
 
return null;

出力された幅と処理平均時間

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