一张100px*100px的图片在内存中会占用多大内存 |
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转: 计算一张100px*100px的图片在内存中会占用多大内存
转: http://www.cnblogs.com/YuangPong/p/6694512.html 在实际开发当中我们经常会忽视如题问题，只是知道图片越小越好，甚至根本不知道如何计算，今天笔者就抛砖引玉一把！ Android中一张图片（Bitmap）占用的内存主要和以下几个因数有关：图片长度，图片宽度，单位像素占用的字节数。 计算方法：一张图片（Bitmap）占用的内存=图片长度*图片宽度*单位像素占用的字节数 长度和宽度不用多做解释 ，单位是像素；关键是单位像素占用的字节数如何获得呢？ 这里不得不提一下Bitmap创建的API Bitmap bitmap = BitmapFactory.decodeResource(Resources res,int id,BitmapFactory.Options opts); 单位像素占用的字节数由其参数BitmapFactory.Options的inPreferredConfig变量决定,默认为Bitmap.Config.ARGB_8888 inPreferredConfig为Bitmap.Config类型， Bitmap.Config类是个枚举类型，它可以为以下值 ALPHA_8Each 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. 此时图片只有alpha值，没有RGB值，一个像素占用1个字节ARGB_4444This field is deprecated. Because of the poor quality of this configuration, it is advised to use ARGB_8888instead. 这种格式的图片，看起来质量太差，已经不推荐使用。 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.) This configuration is mostly useful if the application needs to store translucency information but also needs to save memory. It is recommended to use ARGB_8888 instead of this configuration. 一个像素占用2个字节，alpha(A)值，Red（R）值，Green(G)值，Blue（B）值各占4个bites,共16bites,即2个字节ARGB_8888 Each pixel is stored on 4 bytes. Each channel (RGB and alpha for translucency) is stored with 8 bits of precision (256 possible values.) This configuration is very flexible and offers the best quality. It should be used whenever possible 一个像素占用4个字节，alpha(A)值，Red（R）值，Green(G)值，Blue（B）值各占8个bites,共32bites,即4个字节 这是一种高质量的图片格式，电脑上普通采用的格式。它也是Android手机上一个BitMap的默认格式。RGB_565 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 stored with 6 bits of precision (64 possible values) and blue is stored with 5 bits of precision. This configuration can produce slight visual artifacts depending on the configuration of the source. For instance, without dithering, the result might show a greenish tint. To get better results dithering should be applied. This configuration may be useful when using opaque bitmaps that do not require high color fidelity. 一个像素占用2个字节，没有alpha(A)值，即不支持透明和半透明，Red（R）值占5个bites ，Green(G)值占6个bites ，Blue（B）值占5个bites,共16bites,即2个字节.对于没有透明和半透明颜色的图片来说，该格式的图片能够达到比较的呈现效果，相对于ARGB_8888来说也能减少一半的内存开销。因此它是一个不错的选择。另外我们通过android.content.res.Resources来取得一个张图片时，它也是以该格式来构建BitMap的. 从Android4.0开始，该选项无效。即使设置为该值，系统任然会采用 ARGB_8888来构造图片所以一张100px*100px的图片在内存中占用的内存数为： 图片格式计算公式占用内存大小ALPHA_8100*10010000bARGB_4444100*100*220000bARGB_8888100*100*440000bRGB_565100*100*220000b综上就是今天笔者要分享的小知识，一般这样的问题面试官会问。你get到了吗？ |
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