I use com.google.zxing core to scan an image. RGBLuminanceSource constructor gets int array of pixels, convert it into byte array and "convert the entire image to a greyscale array". I have byte array of pixels and i would like only to convert it.
Can anyone help me with with the gray-scale conversion?
package com.google.zxing;
/**
* This class is used to help decode images from files which arrive as RGB data from
* an ARGB pixel array. It does not support rotation.
*
* @author dswitkin@google.com (Daniel Switkin)
* @author Betaminos
*/
public final class RGBLuminanceSource extends LuminanceSource {
private final byte[] luminances;
private final int dataWidth;
private final int dataHeight;
private final int left;
private final int top;
public RGBLuminanceSource(int width, int height, int[] pixels) {
super(width, height);
dataWidth = width;
dataHeight = height;
left = 0;
top = 0;
// In order to measure pure decoding speed, we convert the entire image to a greyscale array
// up front, which is the same as the Y channel of the YUVLuminanceSource in the real app.
//
// Total number of pixels suffices, can ignore shape
int size = width * height;
luminances = new byte[size];
for (int offset = 0; offset < size; offset++) {
int pixel = pixels[offset];
int r = (pixel >> 16) & 0xff; // red
int g2 = (pixel >> 7) & 0x1fe; // 2 * green
int b = pixel & 0xff; // blue
// Calculate green-favouring average cheaply
luminances[offset] = (byte) ((r + g2 + b) / 4);
}
}
/**
* My constructor
*/
public RGBLuminanceSource(byte[] pixels,
int dataWidth,
int dataHeight
) {
this(pixels,dataWidth,dataHeight,0,0,dataWidth,dataHeight);
// WHAT SHOULD I DO HERE TO "convert the entire image to a greyscale array"?
}
private RGBLuminanceSource(byte[] pixels,
int dataWidth,
int dataHeight,
int left,
int top,
int width,
int height) {
super(width, height);
if (left + width > dataWidth || top + height > dataHeight) {
throw new IllegalArgumentException("Crop rectangle does not fit within image data.");
}
this.luminances = pixels;
this.dataWidth = dataWidth;
this.dataHeight = dataHeight;
this.left = left;
this.top = top;
}
@Override
public byte[] getRow(int y, byte[] row) {
if (y < 0 || y >= getHeight()) {
throw new IllegalArgumentException("Requested row is outside the image: " + y);
}
int width = getWidth();
if (row == null || row.length < width) {
row = new byte[width];
}
int offset = (y + top) * dataWidth + left;
System.arraycopy(luminances, offset, row, 0, width);
return row;
}
@Override
public byte[] getMatrix() {
int width = getWidth();
int height = getHeight();
// If the caller asks for the entire underlying image, save the copy and give them the
// original data. The docs specifically warn that result.length must be ignored.
if (width == dataWidth && height == dataHeight) {
return luminances;
}
int area = width * height;
byte[] matrix = new byte[area];
int inputOffset = top * dataWidth + left;
// If the width matches the full width of the underlying data, perform a single copy.
if (width == dataWidth) {
System.arraycopy(luminances, inputOffset, matrix, 0, area);
return matrix;
}
// Otherwise copy one cropped row at a time.
for (int y = 0; y < height; y++) {
int outputOffset = y * width;
System.arraycopy(luminances, inputOffset, matrix, outputOffset, width);
inputOffset += dataWidth;
}
return matrix;
}
@Override
public boolean isCropSupported() {
return true;
}
@Override
public LuminanceSource crop(int left, int top, int width, int height) {
return new RGBLuminanceSource(luminances,
dataWidth,
dataHeight,
this.left + left,
this.top + top,
width,
height);
}
}
Assuming your pixels
bytes are RGB byte interleaved format, you could do:
public RGBLuminanceSource(byte[] pixels, int width, int height) {
super(width, height);
dataWidth = width;
dataHeight = height;
left = 0;
top = 0;
// Total number of pixels suffices, can ignore shape
int size = width * height;
luminances = new byte[size];
for (int offset = 0; offset < size; offset++) {
int r = pixels[offset * 3 ] & 0xff; // red
int g2 = (pixels[offset * 3 + 1] & 0xff) << 1 // 2 * green
int b = pixels[offset * 3 + 2] & 0xff; // blue
// Calculate green-favouring average cheaply
luminances[offset] = (byte) ((r + g2 + b) / 4);
}
The calculation isn't really the standard way of computing luminance (grayscale) form RGB values, but should produce the same results as with the int packed RGB version.
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