Android Bitmap 图片

热度 ℃

Android中Bitmap图片的显示，是一个比较头疼的问题，Bitmap图片占用内存大，稍不注意就会千万OOM，为什么它会如此占内存呢？

Bitmap.Config

图片的Config，它定义了pixel像素的存储规则，它将直接影响图片的质量。

This affects the quality (color depth) and the ability to display transparent/translucent colors.

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public enum Config {
    // these native values must match up with the enum in SkBitmap.h
    /** 每个像素被存储在一个表示透明度的单通道里面，它不存储颜色值。
     * Each pixel is stored as a single translucency (alpha) channel.
     * This is very useful to efficiently store masks for instance.
     * No color information is stored.
     * With this configuration, each pixel requires 1 byte of memory.
     */
    ALPHA_8     (1), // 每个像素点占用1byte的内存
    /** 每个像素存储在2个byte中，仅存储了RGB通道的颜色值，红绿蓝分别占用5/6/5
     * bit的空间，对应的存储值最大分别是32, 64, 32
     * Each pixel is stored on 2 bytes and only the RGB channels are
     * encoded: red is stored with 5 bits of precision (32 possible
     * values), green is 6(64 possible values) and blue is 5.
     *
     * This configuration can produce slight visual artifacts depending
     * on the configuration of the source.
     * 这个配置通常用于对颜色要求不高的非透明的图片.
     * This configuration may be useful when using opaque bitmaps
     * that do not require high color fidelity.
     */
    RGB_565     (3),
    /** 每个像素存在2个byte中，包含RGB颜色值和alpha透明度值。透明度存在4bit中(最大值16)
     * Each pixel is stored on 2 bytes. The three RGB color channels
     * and the alpha channel (translucency) are stored with a 4 bits
     * precision (16 possible values.)
     * 当应用需要存储透明度值，同时又需要节约内存的时候，使用该配置。
     * 建议使用ARGB_8888代替该配置
     * Note: KITKAT版本之后，使用该配置时，系统将自动使用ARGB_8888配置替换。
     */
    @Deprecated
    ARGB_4444   (4),
    /** 每个像素存储占用4个byte，每个通道(RGB和Alpha)都使用在8bit(最大值256)进行存储。
     * Each pixel is stored on 4 bytes. Each channel (RGB and alpha
     * for translucency) is stored with 8 bits of precision (256
     * possible values.)
     * 推荐使用该配置。
     * This configuration is very flexible and offers the best
     * quality. It should be used whenever possible.
     */
    ARGB_8888   (5),
    /** 每个像素存储占用8个byte。每个通道值存储成float值。
     * Each pixels is stored on 8 bytes. Each channel (RGB and alpha
     * for translucency) is stored as a
     * {@link android.util.Half half-precision floating point value}.
     * 适合用于存储高密度的图片
     * This configuration is particularly suited for wide-gamut and
     * HDR content.
     */
    RGBA_F16    (6),
    /** 一种特殊的配置，图片只被存储在graphic内存区域，并且图片的像素值不能被修改
     * Special configuration, when bitmap is stored only in graphic memory.
     * Bitmaps in this configuration are always immutable.
     * 当一个图片只需要用于显示在screen上，这是最佳的配置。
     */
    HARDWARE    (7);
    private static Config sConfigs[] = {
        null, ALPHA_8, null, RGB_565, ARGB_4444, ARGB_8888, RGBA_F16, HARDWARE
    };
}

生成图片

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public void generateBitmap(@SuppressWarnings("unused") View unused) {
    ByteBuffer buffer = ByteBuffer.allocate(256 * 256 * 4);
    byte[] buffers = buffer.array();
    // 创建4个随机的RGBA颜色值
    byte[][] colors = new byte[4][4];
    for (int i = 0; i < 4; i++) {
        colors[i][0] = (byte) (256 * Math.random() - 128);
        colors[i][1] = (byte) (256 * Math.random() - 128);
        colors[i][2] = (byte) (256 * Math.random() - 128);
        colors[i][3] = (byte) 255; //(byte) (256 * Math.random() - 128);
    }
    // 写入颜色值
    for (int y = 0; y < 256; y++) {
        for (int x = 0; x < 256; x++) {
            int baseIndex = (y * 256 + x) * 4;
            buffers[baseIndex] = colors[x % 4][0];
            buffers[baseIndex + 1] = colors[x % 4][1];
            buffers[baseIndex + 2] = colors[x % 4][2];
            buffers[baseIndex + 3] = colors[x % 4][3];
        }
    }
    Bitmap bmp = Bitmap.createBitmap(256, 256, Bitmap.Config.ARGB_8888);
    bmp.copyPixelsFromBuffer(buffer); // 将颜色值copy到bitmap
    mImageView.setImageBitmap(bmp);
}

其它方法

  • copyPixelsToBuffer: 将Pixel值拷贝到Buffer中
  • copyPixelsFromBuffer: 从Buffer中拷贝Pixel值