为什么保存加载位图增加它的大小？ [英] Why does saving a loaded Bitmap increase it's size?

问题描述

我加载从SD卡的PNG文件。我改变它以某种方式，然后再保存它。我注意到，保存的文件比原来大得多。

起初我还以为是因为修改的文件。然后，我用下面的code测试，仍然发生。

我只是加载PNG文件，然后用另一个名字保存它。

原始文件的 32Kb的并保存的文件为 300KB 。
任何想法？

 尝试
     {位图BM = BitmapFactory.de codeFILE（Environment.getExternalStorageDirectory（）+/Original.png）;
        FileOutputStream中出=新的FileOutputStream（Environment.getExternalStorageDirectory（）+/Saved.png）;
        bm.com preSS（Bitmap.Com pressFormat.PNG，100，出）;
     }
     赶上（例外五）
     {//这里从来没有得到
     }
 

解决方案

您可以控制​​大小的位图的 COM preSS系数（质）：

  Bitmap.com preSS（Bitmap.Com pressFormat格式，诠释品质，FileOutputStream中出）;
 

100 =最高的质量，0 =低质量。

尝试，如10或东西，让您的图像更小。
它也可能是您正在加载一个位图，它是在 16位颜色和不同于稍后保存在 32位的颜色，增加它的大小。

检查 BitmapConfig.RGB_565 ， BitmapConfig.ARGB_4444 和 BitmapConfig.ARGB_8888 分别。

编辑：

下面是如何正确地加载位图：

 公共抽象类Bitma $ P $ {psLoader    公共静态位图德codeBitmapFromResource（Bitmap.Config配置，资源RES，INT渣油，诠释reqWidth，诠释reqHeight）{        最后BitmapFactory.Options选项=新BitmapFactory.Options（）;
        options.inJustDe codeBounds = TRUE;
        BitmapFactory.de codeResource（RES，渣油，期权）;        options.inSampleSize = calculateInSampleSize（选项，reqWidth，reqHeight）;        //德code位与inSampleSize集
        options.inJustDe codeBounds = FALSE;
        options.in preferredConfig =配置;        返回BitmapFactory.de codeResource（RES，渣油，期权）;
    }    私有静态诠释calculateInSampleSize（
                BitmapFactory.Options选项，诠释reqWidth，诠释reqHeight）{
        //原始高度和图像宽度
        最终诠释身高= options.outHeight;
        最终诠释宽度= options.outWidth;
        INT inSampleSize = 1;        如果（高度＆GT; reqHeight ||宽度GT; reqWidth）{            //计算的高度和宽度的比率要求的高度和宽度
            最终诠释heightRatio = Math.round（（浮点）高度/（浮点）reqHeight）;
            最终诠释widthRatio = Math.round（（浮点）宽/（浮点）reqWidth）;            //选择最小比率inSampleSize值，这将保证
            //使用两个维度大于或等于所述最终图像
            //请求的高度和宽度。
            inSampleSize = heightRatio＆LT; widthRatio？ heightRatio：widthRatio;
        }        返回inSampleSize;
    }
}
 

在code：

  // Bitmap.Config.RGB_565 = 16位
位图B = Bitma presLoader.de codeBitmapFromResource（Bitmap.Config.RGB_565，getResources（），宽，高）;
 

这样的话，你可以控制你如何位图被加载到内存（请参阅 Bitmap.Config ）

I load a png file from the sdcard. I alter it in someway and then save it again. I have noticed that the saved file is much larger than the original.

At first I thought it was because of modifying the file. Then I tested with the code below and still happens.

I just load a png file and then save it with another name.

The Original file is 32Kb and the Saved file is 300Kb. Any ideas?

     try
     {  Bitmap bm = BitmapFactory.decodeFile(Environment.getExternalStorageDirectory() + "/Original.png");
        FileOutputStream out = new FileOutputStream(Environment.getExternalStorageDirectory() + "/Saved.png"); 
        bm.compress(Bitmap.CompressFormat.PNG, 100, out);
     } 
     catch (Exception e)
     {  //Never gets here
     }

解决方案

You can control the size of your Bitmap by the compress factor (quality):

Bitmap.compress(Bitmap.CompressFormat format, int quality, FileOutputStream out);

100 = maximum quality, 0 = low quality.

Try like "10" or something to keep your image smaller. It could also be that you are loading a Bitmap that is in 16-Bit color and than later save it in 32-Bit color, increasing its size.

Check BitmapConfig.RGB_565, BitmapConfig.ARGB_4444 and BitmapConfig.ARGB_8888 respectively.

EDIT:

Here is how to load Bitmaps correctly:

public abstract class BitmapResLoader {

    public static Bitmap decodeBitmapFromResource(Bitmap.Config config, Resources res, int resId, int reqWidth, int reqHeight) {

        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeResource(res, resId, options);

        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

        // Decode bitmap with inSampleSize set
        options.inJustDecodeBounds = false;
        options.inPreferredConfig = config;

        return BitmapFactory.decodeResource(res, resId, options);
    }

    private static int calculateInSampleSize(
                BitmapFactory.Options options, int reqWidth, int reqHeight) {
        // Raw height and width of image
        final int height = options.outHeight;
        final int width = options.outWidth;
        int inSampleSize = 1;

        if (height > reqHeight || width > reqWidth) {

            // Calculate ratios of height and width to requested height and width
            final int heightRatio = Math.round((float) height / (float) reqHeight);
            final int widthRatio = Math.round((float) width / (float) reqWidth);

            // Choose the smallest ratio as inSampleSize value, this will guarantee
            // a final image with both dimensions larger than or equal to the
            // requested height and width.
            inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;
        }

        return inSampleSize;
    }
}

In code:

// Bitmap.Config.RGB_565 = 16 Bit
Bitmap b = BitmapResLoader.decodeBitmapFromResource(Bitmap.Config.RGB_565, getResources(), width, height);

That way, you can control how your Bitmap is loaded into Memory (see Bitmap.Config).

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