Java Encode encodeRGBAsGrayScale(final byte[] raw, final int width, final int height, final int bitsPerPixel, final OutputStream out)

Description

Converts a byte array containing 24 bit RGB image data to a grayscale image.

License

Apache License

Parameter

Parameter	Description
raw	the buffer containing the RGB image data
width	the width of the image in pixels
height	the height of the image in pixels
bitsPerPixel	the number of bits to use per pixel
out	the OutputStream to write the pixels to

Exception

Parameter	Description
IOException	if an I/O error occurs

Declaration

public static void encodeRGBAsGrayScale(final byte[] raw, final int width, final int height,
        final int bitsPerPixel, final OutputStream out) throws IOException 

Method Source Code

//package com.java2s;
/*//from   w  w  w  . ja  va2 s. c om
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.io.OutputStream;

public class Main {
    /**
     * Converts a byte array containing 24 bit RGB image data to a grayscale
     * image.
     *
     * @param raw
     *            the buffer containing the RGB image data
     * @param width
     *            the width of the image in pixels
     * @param height
     *            the height of the image in pixels
     * @param bitsPerPixel
     *            the number of bits to use per pixel
     * @param out
     *            the OutputStream to write the pixels to
     *
     * @throws IOException
     *             if an I/O error occurs
     */
    public static void encodeRGBAsGrayScale(final byte[] raw, final int width, final int height,
            final int bitsPerPixel, final OutputStream out) throws IOException {
        final int pixelsPerByte = 8 / bitsPerPixel;
        int bytewidth = width / pixelsPerByte;
        if (width % pixelsPerByte != 0) {
            bytewidth++;
        }

        // TODO Rewrite to encode directly from a RenderedImage to avoid
        // buffering the whole RGB
        // image in memory
        final byte[] linedata = new byte[bytewidth];
        byte ib;
        for (int y = 0; y < height; y++) {
            ib = 0;
            int i = 3 * y * width;
            for (int x = 0; x < width; x++, i += 3) {

                // see http://www.jguru.com/faq/view.jsp?EID=221919
                double greyVal = 0.212671d * (raw[i] & 0xff) + 0.715160d * (raw[i + 1] & 0xff)
                        + 0.072169d * (raw[i + 2] & 0xff);
                switch (bitsPerPixel) {
                case 1:
                    if (greyVal < 128) {
                        ib |= (byte) (1 << 7 - x % 8);
                    }
                    break;
                case 4:
                    greyVal /= 16;
                    ib |= (byte) ((byte) greyVal << (1 - x % 2) * 4);
                    break;
                case 8:
                    ib = (byte) greyVal;
                    break;
                default:
                    throw new UnsupportedOperationException("Unsupported bits per pixel: " + bitsPerPixel);
                }

                if (x % pixelsPerByte == pixelsPerByte - 1 || x + 1 == width) {
                    linedata[x / pixelsPerByte] = ib;
                    ib = 0;
                }
            }
            out.write(linedata);
        }
    }
}

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