我正在使用类似于 Java - get pixel array from image 的代码获取对 BMP 图像像素数据的低级访问,如下所示:
BufferedImage image = ImageIO.read(is);
DataBuffer buffer = image.getRaster().getDataBuffer();
byte[] rawPixels = ((DataBufferByte) buffer).getData();
结果数组从下到上放置(即它的第一个字节是最后一个图像行的开头),考虑到BMP files usually have the same layout,这是有道理的。 .
在这种情况下,我想通过翻转线路来向调用者隐藏这些低级细节。有没有办法可以查询加载的 BufferedImage 的像素方向/布局?
最佳答案
我检查了 Java 7 BMPImageReader
的源代码,它在读取时确实从下到上的顺序转换为自上而下的顺序,正如我所期望的那样。因此,DataBuffer 的后备数组将采用正常的自上而下的顺序。我无法在 Windows 上使用 Oracle Java 7 JRE 重现此行为。
OP 已验证问题确实存在于代码的另一部分,而不是作为问题的一部分发布。
我认为所描述的内容可能是可能的,使用 SampleModel
的特殊子类来转换所有传入的 y 坐标,但没有标准方法来查询方向(所有 Rasters
假定为自上而下)。
无论如何,只是为了好玩,我创建了一些代码来测试它是否可能。下面是一个完全可运行的示例。
public class SampleModelOrientationTest {
public static void main(String[] args) {
BufferedImage image = new BufferedImage(16, 9, BufferedImage.TYPE_3BYTE_BGR);
WritableRaster raster = image.getRaster();
DataBuffer dataBuffer = raster.getDataBuffer();
SampleModel sampleModel = image.getSampleModel();
QueryingDataBuffer queryBuffer = new QueryingDataBuffer(dataBuffer, sampleModel.getWidth(), sampleModel.getNumDataElements());
sampleModel.getDataElements(0, 0, null, queryBuffer);
System.out.println(queryBuffer.getOrientation());
queryBuffer.resetOrientation();
SampleModel bottomUpSampleModel = new BottomUpSampleModel(sampleModel);
bottomUpSampleModel.getDataElements(0, 0, null, queryBuffer);
System.out.println(queryBuffer.getOrientation());
}
private static class QueryingDataBuffer extends DataBuffer {
enum Orientation {
Undefined,
TopDown,
BottomUp,
Unsupported
}
private final int width;
private final int numDataElements;
private Orientation orientation = Orientation.Undefined;
public QueryingDataBuffer(final DataBuffer dataBuffer, final int width, final int numDataElements) {
super(dataBuffer.getDataType(), dataBuffer.getSize());
this.width = width;
this.numDataElements = numDataElements;
}
@Override public int getElem(final int bank, final int i) {
if (bank == 0 && i < numDataElements && isOrientationUndefinedOrEqualTo(Orientation.TopDown)) {
orientation = Orientation.TopDown;
}
else if (bank == 0 && i >= (size - (width * numDataElements) - numDataElements) && isOrientationUndefinedOrEqualTo(Orientation.BottomUp)) {
orientation = Orientation.BottomUp;
}
else {
// TODO: Expand with more options as apropriate
orientation = Orientation.Unsupported;
}
return 0;
}
private boolean isOrientationUndefinedOrEqualTo(final Orientation orientation) {
return this.orientation == Orientation.Undefined || this.orientation == orientation;
}
@Override public void setElem(final int bank, final int i, final int val) {
}
public final void resetOrientation() {
orientation = Orientation.Undefined;
}
public final Orientation getOrientation() {
return orientation;
}
}
// TODO: This has to be generalized to be used for any BufferedImage type.
// I justy happen to know that 3BYTE_BGR uses PixelInterleavedSampleModel and has BGR order.
private static class BottomUpSampleModel extends PixelInterleavedSampleModel {
public BottomUpSampleModel(final SampleModel sampleModel) {
super(sampleModel.getDataType(), sampleModel.getWidth(), sampleModel.getHeight(),
sampleModel.getNumDataElements(), sampleModel.getNumDataElements() * sampleModel.getWidth(),
new int[] {2, 1, 0} // B, G, R
);
}
@Override public Object getDataElements(final int x, final int y, final Object obj, final DataBuffer data) {
return super.getDataElements(x, getHeight() - 1 - y, obj, data);
}
@Override public int getSample(final int x, final int y, final int b, final DataBuffer data) {
return super.getSample(x, getHeight() - 1 - y, b, data);
}
}
}
关于java - 查询图像方向,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/23525626/