一：数学原理
当一幅二维数字图像从源图像N*M被放为(j*N) * (k*M)目标图像是，参照数学斜率计算公式
必然有:
(X1 – Xmin)/(Xmax - Xmin) = (Y1 - Ymin)/(Ymax-Ymin)
当Xmin 和 Ymin均为从零开始的像素点时，公式可以简化为:
X=Y1 (Xmax/Ymax)
对于任意一幅源图像来说，假设放大后目标图像的宽为Dw高为Dh,任意目标像素点(Dx, Dy)
在源图像上的位置为:
Sx= Dx * (Sh/Dh) // row
Sy= Dy * (Sw/Dw) // column
其中，(Sx,Sy)为对于的源图像上的像素点，Sw和Sh分别为源图像的宽度和高度。最终有
Dpixel(Dx,Dy) = Spixel(Sx, Sy);
二：临近点插值算法的缺点
临近点插值算法会产生锯齿效果, 不是一个很好的图像放缩算法，临近点插值算法不改变源
像素点到目标像素点的值，只是最简单的位置匹配而已，相比之下，双线性内插值算法和双
立方插值算法效果更好，但是计算量更大，临近点插值是计算量最小的防缩算法。
三：关键程序代码解释
从BufferedImage对象中获取像素数组的代码如下：
int type = img.getType();
if ( type == BufferedImage.TYPE_INT_ARGB ||
type == BufferedImage.TYPE_INT_RGB ) {
img.getRaster().setDataElements(x, y,width,height, pixelsData);
}
else {
img.setRGB(x, y, width, height, pixelsData, 0, width);
}
从源图像对象一维像素数组转换为三维对象数组，代码如下：
int[][][] tempData = new int[imgRows][imgCols][4];
tempData[row][col][0] =(aRow[col] >> 24) & 0xFF; // alpha
tempData[row][col][1] =(aRow[col] >> 16) & 0xFF; // red
tempData[row][col][2] =(aRow[col] >> 8) & 0xFF; // green
tempData[row][col][3] = (aRow[col]) &0xFF; // blue
首先要计算行与列的缩放比例，计算代码如下：
float rowRatio = ((float)srcH)/((float)destH);
float colRatio = ((float)srcW)/((float)destW);
计算源像素点的行位置：
int srcRow = Math.round(((float)row)*rowRatio);
计算源像素点的列位置：
int srcCol = Math.round(((float)col)*colRatio);
四：程序效果
五：程序源代码
public class NearNaighborZoom implements ImageScale {
public NearNaighborZoom() {
}
/**
* (X-Xmin)/(Xmax-Xmin) = (Y-Ymin)/(Ymax-Ymin)
* assume Xmin and Ymin are zero, then the formula will be f(x) = kx (k - coefficent, slope)
*
*/
@Override
public int[] imgScale(int[] inPixelsData, int srcW, int srcH, int destW, int destH) {
int[][][] inputThreeDeminsionData = processOneToThreeDeminsion(inPixelsData, srcH, srcW);
int[][][] outputThreeDeminsionData = new int[destH][destW][4];
float rowRatio = ((float)srcH)/((float)destH);
float colRatio = ((float)srcW)/((float)destW);
for(int row=0; row<destH; row++) {
// convert to three dimension data
int srcRow = Math.round(((float)row)*rowRatio);
if(srcRow >=srcH) {
srcRow = srcH - 1;
}
for(int col=0; col<destW; col++) {
int srcCol = Math.round(((float)col)*colRatio);
if(srcCol >= srcW) {
srcCol = srcW - 1;
}
outputThreeDeminsionData[row][col][0] = inputThreeDeminsionData[srcRow][srcCol][0]; // alpha
outputThreeDeminsionData[row][col][1] = inputThreeDeminsionData[srcRow][srcCol][1]; // red
outputThreeDeminsionData[row][col][2] = inputThreeDeminsionData[srcRow][srcCol][2]; // green
outputThreeDeminsionData[row][col][3] = inputThreeDeminsionData[srcRow][srcCol][3]; // blue
}
}
return convertToOneDim(outputThreeDeminsionData, destW, destH);
}
/* <p> The purpose of this method is to convert the data in the 3D array of ints back into </p>
* <p> the 1d array of type int. </p>
*
*/
public int[] convertToOneDim(int[][][] data, int imgCols, int imgRows) {
// Create the 1D array of type int to be populated with pixel data
int[] oneDPix = new int[imgCols * imgRows * 4];
// Move the data into the 1D array. Note the
// use of the bitwise OR operator and the
// bitwise left-shift operators to put the
// four 8-bit bytes into each int.
for (int row = 0, cnt = 0; row < imgRows; row++) {
for (int col = 0; col < imgCols; col++) {
oneDPix[cnt] = ((data[row][col][0] << 24) & 0xFF000000)
| ((data[row][col][1] << 16) & 0x00FF0000)
| ((data[row][col][2] << 8) & 0x0000FF00)
| ((data[row][col][3]) & 0x000000FF);
cnt++;
}// end for loop on col
}// end for loop on row
return oneDPix;
}// end convertToOneDim
private int[][][] processOneToThreeDeminsion(int[] oneDPix2, int imgRows, int imgCols) {
int[][][] tempData = new int[imgRows][imgCols][4];
for(int row=0; row<imgRows; row++) {
// per row processing
int[] aRow = new int[imgCols];
for (int col = 0; col < imgCols; col++) {
int element = row * imgCols + col;
aRow[col] = oneDPix2[element];
}
// convert to three dimension data
for(int col=0; col<imgCols; col++) {
tempData[row][col][0] = (aRow[col] >> 24) & 0xFF; // alpha
tempData[row][col][1] = (aRow[col] >> 16) & 0xFF; // red
tempData[row][col][2] = (aRow[col] >> 8) & 0xFF; // green
tempData[row][col][3] = (aRow[col]) & 0xFF; // blue
}
}
return tempData;
}
}
