Android 图片加载

加载图片大小的计算

width * height * inTargetDensity/inDensity * inTargetDensity/inDensity * 一个像素所占的内存。
Android 默认图片类型：ARGB_8888(每个像素占用4byte内存)

BitmapFactory.Options options = new BitmapFactory.Options();

                Bitmap bitmap = BitmapFactory.decodeResource(getResources(),R.drawable.p1,options);
                Log.e(TAG, "width:" + options.outWidth + ":::height:" + options.outHeight);
                Log.e(TAG, "bitmap：ByteCount = "+bitmap.getAllocationByteCount());
                Log.e(TAG, "inDensity:" + options.inDensity + ":::inTargetDensity:" + options.inTargetDensity);

width:1311:::height:882
bitmap：ByteCount = 56664972
inDensity:160:::inTargetDensity:560

image.png

56664972/1311/882/4 =12.251.. 560/160 * 560/160 = 12.25

Android 图片类型

ALPHA_8：每个像素占用1byte内存。
ARGB_4444:每个像素占用2byte内存
ARGB_8888:每个像素占用4byte内存
RGB_565:每个像素占用2byte内存

Android 默认图片是ARGB_8888

Bitmap 占用内存

getByteCount()
getAllocationByteCount() 取代上面方法

对于webp的尝试

目前网络中图片仍然是占用流量较大的一部分，对于移动端更是如此，因此，如何在保证图片视觉不失真前提下缩小体积，对于节省带宽和电池电量十分重要。

WebP为网络图片提供了无损和有损压缩能力，同时在有损条件下支持透明通道。据官方实验显示：无损WebP相比PNG减少26%大小；有损WebP在相同的SSIM（Structural Similarity Index，结构相似性）下相比JPEG减少25%~34%的大小；有损WebP也支持透明通道，大小通常约为对应PNG的1/3。 同时，谷歌于2014年提出了动态WebP，拓展WebP使其支持动图能力。动态WebP相比GIF支持更丰富的色彩，并且也占用更小空间，更适应移动网络的动图播放。

作者：腾讯Bugly
链接：https://www.zhihu.com/question/27201061/answer/133992530

public class MainActivity extends AppCompatActivity {



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        String path = getApplicationContext().getFilesDir().getAbsolutePath();
        byte[] bytes = compressBitmapToBytes(600,0,100, Bitmap.CompressFormat.JPEG);
        Bitmap bp = BitmapFactory.decodeByteArray(bytes,0,bytes.length);
        saveBitmap(bp,path,"jpg");
        saveBitmap(bp,path,"webp");



    }

    private Bitmap.CompressFormat compressFormat(String type){

        switch (type){
            case "jpg":
                return Bitmap.CompressFormat.JPEG;
            case "webp":
                return Bitmap.CompressFormat.WEBP;
            default:
                 return Bitmap.CompressFormat.JPEG;
        }
    }

    public void saveBitmap(Bitmap bitmap,String path,String type){

        File file = new File(path,"test");
        if (!file.exists()) {
            //通过file的mkdirs()方法创建目录中包含却不存在的文件夹
            file.mkdirs();
        }

        File picture = new File(file+"/"+"1."+type);
        FileOutputStream out = null;
        try {
            out = new FileOutputStream(picture);
            long starten=System.currentTimeMillis();   //获取开始时间
            bitmap.compress(compressFormat(type), 100,
                    out);
            long enden=System.currentTimeMillis(); //获取结束时间
            Log.e("编码运行时间： ",(enden-starten)+"ms");
            out.close();

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public byte[] compressBitmapToBytes(int reqWidth, int reqHeight, int quality, Bitmap.CompressFormat format) {
        Bitmap bitmap = getSmallBitmap( reqWidth, reqHeight);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        bitmap.compress(format, quality, baos);
        byte[] bytes = baos.toByteArray();
        bitmap.recycle();
        Log.i("compress", "Bitmap compressed success, size: " + bytes.length);
        return bytes;
    }

    public Bitmap getSmallBitmap(int reqWidth, int reqHeight) {
        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        Bitmap bp = BitmapFactory.decodeResource(getResources(),R.drawable.p1,options);
        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
        options.inJustDecodeBounds = false;
        return BitmapFactory.decodeResource(getResources(),R.drawable.p1,options);
    }

    public  int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
        int h = options.outHeight;
        int w = options.outWidth;
        int inSampleSize = 0;
        if (h > reqHeight || w > reqWidth) {
            float ratioW = (float) w / reqWidth;
            float ratioH = (float) h / reqHeight;
            inSampleSize = (int) Math.min(ratioH, ratioW);
        }
        inSampleSize = Math.max(1, inSampleSize);
        return inSampleSize;
    }
}

image.png image.png

webp 压缩能力确实强 但是在android 端 编码时间太长