详解Android Bitmap的使用

亦凉 2022-10-30 11:26 206阅读 0赞

一 图片表示原理  
图片是由每个像素点来组成 像素点就是小方块

图片的大小等于 宽\*高\*每个像素点的大小

二 加载图片OOM异常

解决办法

其中big.jpg是一张21.2MB的高清图

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public class MainActivity extends AppCompatActivity implements View.OnClickListener \{  
  
ImageView mImageView;  
  
@Override  
protected void onCreate(Bundle savedInstanceState) \{  
super.onCreate(savedInstanceState);  
setContentView(R.layout.activity\_main);  
  
findViewById(R.id.load).setOnClickListener(this);  
mImageView = findViewById(R.id.image);  
\}  
  
@Override  
public void onClick(View view) \{  
switch (view.getId()) \{  
case R.id.load:  
load();  
break;  
\}  
\}  
  
private void load() \{  
try \{  
BitmapFactory.Options option = new BitmapFactory.Options();  
option.inJustDecodeBounds = true; //只会解析图片的大小 不会加载图片的内容  
BitmapFactory.decodeStream(getAssets().open("big.jpg"), null, option);  
// 获取图片的宽高  
int width = option.outWidth;  
int height = option.outHeight;  
// 获取屏幕的宽高  
int screenWidth = getScreenWidth();  
int screenHeight = getScreenHeight();  
// 把图片的宽高和屏幕的宽高进行对比  
int scaleX = width / screenWidth;  
int scaleY = height / screenHeight;  
int scale = scaleX > scaleY ? scaleX : scaleY;  
option.inJustDecodeBounds = false; //加载图片的内容  
// 如果设置为>1 请求解码器对原始数据进行子采样 例如inSampleSize==4返回图像的宽度/高度是原始图像的1/4  
// 任何值<=1都与1相同  
option.inSampleSize = scale;  
Bitmap bitmap = BitmapFactory.decodeStream(getAssets().open("big.jpg"), null, option);  
int byteCount = bitmap.getByteCount();  
Log.i("HUANG", "byteCount=" + byteCount);  
mImageView.setImageBitmap(bitmap);  
  
\} catch (IOException e) \{  
e.printStackTrace();  
\}  
\}  
  
/\*\* 得到设备屏幕的宽度 (像素) \*\*/  
private int getScreenWidth() \{  
return getResources().getDisplayMetrics().widthPixels;  
\}  
  
/\*\* 得到设备屏幕的高度 (像素) \*\*/  
private int getScreenHeight() \{  
return getResources().getDisplayMetrics().heightPixels;  
\}  
  
\}  
三 图片处理原理  
Android里面所有的显示效果都是绘制出来的

用Android封装好的绘图类去绘制图片

Canvas: 画布

Paint: 画笔

Matrix: 图形矩阵 3\*3

Bitmap: 要绘制的图片

四 图片的旋转 平移 缩放  
其中mm.jpg是一张57KB的图 属于正常范围 不需要额外处理

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public class MainActivity extends AppCompatActivity implements View.OnClickListener \{  
  
ImageView mImageView, mCopyView;  
Bitmap mBitmap;  
  
@Override  
protected void onCreate(Bundle savedInstanceState) \{  
super.onCreate(savedInstanceState);  
setContentView(R.layout.activity\_main);  
  
findViewById(R.id.change).setOnClickListener(this);  
mImageView = findViewById(R.id.image);  
mCopyView = findViewById(R.id.copy);  
try \{  
mBitmap = BitmapFactory.decodeStream(getAssets().open("mm.jpg"));  
mImageView.setImageBitmap(mBitmap);  
\} catch (IOException e) \{  
e.printStackTrace();  
\}  
\}  
  
@Override  
public void onClick(View view) \{  
switch (view.getId()) \{  
case R.id.change:  
change();  
break;  
\}  
\}  
  
// 图片的旋转 平移 缩放  
// 注意: 旋转 平移 缩放 这三种效果在本案例中只能同时存在一种 分别打开注释看效果  
private void change() \{  
if (null == mBitmap) return;  
// 新建空白的图片 要和原图的大小一样  
Bitmap bitmap = Bitmap.createBitmap(mBitmap.getWidth(), mBitmap.getHeight(), mBitmap.getConfig());  
Canvas canvas = new Canvas(bitmap); //画布 传参必须是一个空白的图片 否则报错  
Paint paint = new Paint(); //画笔  
Matrix matrix = new Matrix(); //矩阵  
// 旋转30度 以图片的中心为圆心  
matrix.setRotate(30, mBitmap.getWidth() / 2, mBitmap.getHeight() / 2);  
// X轴平移80  
//matrix.setTranslate(80, 0);  
// Y轴缩为原来的0.5  
//matrix.setScale(1F, 0.5F, mBitmap.getWidth() / 2, mBitmap.getHeight() / 2);  
canvas.drawColor(Color.WHITE); //绘制背景为白色  
canvas.drawBitmap(mBitmap, matrix, paint); //绘制图片  
mCopyView.setImageBitmap(bitmap);  
\}  
  
\}  
五 图片的涂鸦操作  
其中mm.jpg是一张57KB的图 属于正常范围 不需要额外处理

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public class MainActivity extends AppCompatActivity implements View.OnTouchListener \{  
  
ImageView mImageView;  
Bitmap mNewBitmap;  
Canvas mCanvas;  
Paint mPaint;  
Matrix mMatrix;  
int mStartX, mStartY; //按下点的坐标  
  
@Override  
protected void onCreate(Bundle savedInstanceState) \{  
super.onCreate(savedInstanceState);  
setContentView(R.layout.activity\_main);  
  
mImageView = findViewById(R.id.image);  
try \{  
Bitmap bitmap = BitmapFactory.decodeStream(getAssets().open("mm.jpg"));  
// 不能直接在原图上进行绘制 必须新建空白的图片  
mNewBitmap = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), bitmap.getConfig());  
mCanvas = new Canvas(mNewBitmap);  
mPaint = new Paint();  
mPaint.setColor(Color.YELLOW);  
mMatrix = new Matrix();  
// 把原图绘制在空白的图片上  
mCanvas.drawBitmap(bitmap, mMatrix, mPaint);  
mImageView.setImageBitmap(mNewBitmap);  
mImageView.setOnTouchListener(this); //设置触摸监听  
  
\} catch (IOException e) \{  
e.printStackTrace();  
\}  
\}  
  
@Override  
public boolean onTouch(View v, MotionEvent event) \{  
switch (event.getAction()) \{  
case MotionEvent.ACTION\_DOWN: //按下  
mStartX = (int) event.getX();  
mStartY = (int) event.getY();  
break;  
  
case MotionEvent.ACTION\_MOVE: //移动  
// 获取移动点的坐标  
int moveX = (int) event.getX();  
int moveY = (int) event.getY();  
// 画线  
mCanvas.drawLine(mStartX, mStartY, moveX, moveY, mPaint);  
// 把新图设置给ImageView  
mImageView.setImageBitmap(mNewBitmap);  
// 把移动点置为开始点  
mStartX = moveX;  
mStartY = moveY;  
break;  
  
case MotionEvent.ACTION\_UP: //弹起  
break;  
\}  
return true; //事件自己来处理  
\}  
  
\}  
六 图片的颜色处理  
图片是有颜色

核心原理就是重绘图片

改变图片的颜色就是对画笔进行操

其中mm.jpg是一张57KB的图 属于正常范围 不需要额外处理

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public class MainActivity extends AppCompatActivity implements View.OnClickListener \{  
  
ImageView mImageView;  
Bitmap mBitmap, mNewBitmap;  
Canvas mCanvas;  
Paint mPaint;  
  
@Override  
protected void onCreate(Bundle savedInstanceState) \{  
super.onCreate(savedInstanceState);  
setContentView(R.layout.activity\_main);  
  
mImageView = findViewById(R.id.image);  
try \{  
mBitmap = BitmapFactory.decodeStream(getAssets().open("mm.jpg"));  
mImageView.setImageBitmap(mBitmap);  
mNewBitmap = Bitmap.createBitmap(mBitmap.getWidth(), mBitmap.getHeight(), mBitmap.getConfig());  
mCanvas = new Canvas(mNewBitmap);  
mPaint = new Paint();  
findViewById(R.id.change).setOnClickListener(this);  
  
\} catch (IOException e) \{  
e.printStackTrace();  
\}  
\}  
  
@Override  
public void onClick(View view) \{  
switch (view.getId()) \{  
case R.id.change:  
int randomR = (int) (Math.random() \* 256); //0-255 随机数  
int randomG = (int) (Math.random() \* 256); //0-255 随机数  
int randomB = (int) (Math.random() \* 256); //0-255 随机数  
int randomA = (int) (Math.random() \* 256); //0-255 随机数  
float colorR = (255 - randomR) / (float) 255;  
float colorG = (255 - randomG) / (float) 255;  
float colorB = (255 - randomB) / (float) 255;  
float colorA = (255 - randomA) / (float) 255;  
Log.i("HUANG", "randomR=" + randomR);  
Log.i("HUANG", "randomG=" + randomG);  
Log.i("HUANG", "randomB=" + randomB);  
Log.i("HUANG", "randomA=" + randomA);  
Log.i("HUANG", "colorR=" + colorR);  
Log.i("HUANG", "colorG=" + colorG);  
Log.i("HUANG", "colorB=" + colorB);  
Log.i("HUANG", "colorA=" + colorA);  
  
ColorMatrix matrix = new ColorMatrix(); //颜色矩阵 5\*4  
matrix.set(new float\[\]\{  
colorR, 0, 0, 0, 0, //red  
0, colorG, 0, 0, 0, //green  
0, 0, colorB, 0, 0, //blue  
0, 0, 0, colorA, 0 //alpha  
\});  
ColorMatrixColorFilter filter = new ColorMatrixColorFilter(matrix);  
mPaint.setColorFilter(filter);  
mCanvas.drawBitmap(mBitmap, new Matrix(), mPaint);  
mImageView.setImageBitmap(mNewBitmap);  
break;  
\}  
\}  
  
\}