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The Apache PDFBox library is an open source Java tool for working with PDF documents.
/*
* 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.
*/
package org.apache.pdfbox.filter;
import java.awt.image.BufferedImage;
import java.awt.image.DataBufferByte;
import java.awt.image.Raster;
import java.awt.image.WritableRaster;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import javax.imageio.IIOException;
import javax.imageio.ImageIO;
import javax.imageio.ImageReadParam;
import javax.imageio.ImageReader;
import javax.imageio.metadata.IIOMetadata;
import javax.imageio.metadata.IIOMetadataNode;
import javax.imageio.stream.ImageInputStream;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.pdfbox.cos.COSDictionary;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;
/**
* Decompresses data encoded using a DCT (discrete cosine transform)
* technique based on the JPEG standard.
*
* @author John Hewson
*/
final class DCTFilter extends Filter
{
private static final Log LOG = LogFactory.getLog(DCTFilter.class);
private static final int POS_TRANSFORM = 11;
private static final String ADOBE = "Adobe";
@Override
public DecodeResult decode(InputStream encoded, OutputStream decoded, COSDictionary
parameters, int index, DecodeOptions options) throws IOException
{
ImageReader reader = findImageReader("JPEG", "a suitable JAI I/O image filter is not installed");
ImageInputStream iis = null;
try
{
iis = ImageIO.createImageInputStream(encoded);
// skip one LF if there
if (iis.read() != 0x0A)
{
iis.seek(0);
}
reader.setInput(iis);
ImageReadParam irp = reader.getDefaultReadParam();
irp.setSourceSubsampling(options.getSubsamplingX(), options.getSubsamplingY(),
options.getSubsamplingOffsetX(), options.getSubsamplingOffsetY());
irp.setSourceRegion(options.getSourceRegion());
options.setFilterSubsampled(true);
String numChannels = getNumChannels(reader);
// get the raster using horrible JAI workarounds
ImageIO.setUseCache(false);
Raster raster;
// Strategy: use read() for RGB or "can't get metadata"
// use readRaster() for CMYK and gray and as fallback if read() fails
// after "can't get metadata" because "no meta" file was CMYK
if ("3".equals(numChannels) || numChannels.isEmpty())
{
try
{
// I'd like to use ImageReader#readRaster but it is buggy and can't read RGB correctly
BufferedImage image = reader.read(0, irp);
raster = image.getRaster();
}
catch (IIOException e)
{
// JAI can't read CMYK JPEGs using ImageReader#read or ImageIO.read but
// fortunately ImageReader#readRaster isn't buggy when reading 4-channel files
raster = reader.readRaster(0, irp);
}
}
else
{
// JAI can't read CMYK JPEGs using ImageReader#read or ImageIO.read but
// fortunately ImageReader#readRaster isn't buggy when reading 4-channel files
raster = reader.readRaster(0, irp);
}
// special handling for 4-component images
if (raster.getNumBands() == 4)
{
// get APP14 marker
Integer transform;
try
{
transform = getAdobeTransform(reader.getImageMetadata(0));
}
catch (IIOException e)
{
// we really tried asking nicely, now we're using brute force.
transform = getAdobeTransformByBruteForce(iis);
}
catch (NegativeArraySizeException e)
{
// we really tried asking nicely, now we're using brute force.
transform = getAdobeTransformByBruteForce(iis);
}
int colorTransform = transform != null ? transform : 0;
// 0 = Unknown (RGB or CMYK), 1 = YCbCr, 2 = YCCK
switch (colorTransform)
{
case 0:
// already CMYK
break;
case 1:
raster = fromYCbCrtoCMYK(raster);
break;
case 2:
raster = fromYCCKtoCMYK(raster);
break;
default:
throw new IllegalArgumentException("Unknown colorTransform");
}
}
else if (raster.getNumBands() == 3)
{
// BGR to RGB
raster = fromBGRtoRGB(raster);
}
DataBufferByte dataBuffer = (DataBufferByte)raster.getDataBuffer();
decoded.write(dataBuffer.getData());
}
finally
{
if (iis != null)
{
iis.close();
}
reader.dispose();
}
return new DecodeResult(parameters);
}
@Override
public DecodeResult decode(InputStream encoded, OutputStream decoded,
COSDictionary parameters, int index) throws IOException
{
return decode(encoded, decoded, parameters, index, DecodeOptions.DEFAULT);
}
// reads the APP14 Adobe transform tag and returns its value, or 0 if unknown
private Integer getAdobeTransform(IIOMetadata metadata)
{
Element tree = (Element)metadata.getAsTree("javax_imageio_jpeg_image_1.0");
Element markerSequence = (Element)tree.getElementsByTagName("markerSequence").item(0);
NodeList app14AdobeNodeList = markerSequence.getElementsByTagName("app14Adobe");
if (app14AdobeNodeList != null && app14AdobeNodeList.getLength() > 0)
{
Element adobe = (Element) app14AdobeNodeList.item(0);
return Integer.parseInt(adobe.getAttribute("transform"));
}
return 0;
}
// See in https://github.com/haraldk/TwelveMonkeys
// com.twelvemonkeys.imageio.plugins.jpeg.AdobeDCT class for structure of APP14 segment
private int getAdobeTransformByBruteForce(ImageInputStream iis) throws IOException
{
int a = 0;
iis.seek(0);
int by;
while ((by = iis.read()) != -1)
{
if (ADOBE.charAt(a) == by)
{
++a;
if (a != ADOBE.length())
{
continue;
}
// match
a = 0;
long afterAdobePos = iis.getStreamPosition();
iis.seek(iis.getStreamPosition() - 9);
int tag = iis.readUnsignedShort();
if (tag != 0xFFEE)
{
iis.seek(afterAdobePos);
continue;
}
int len = iis.readUnsignedShort();
if (len >= POS_TRANSFORM + 1)
{
byte[] app14 = new byte[Math.max(len, POS_TRANSFORM + 1)];
if (iis.read(app14) >= POS_TRANSFORM + 1)
{
return app14[POS_TRANSFORM];
}
}
}
else
{
a = 0;
}
}
return 0;
}
// converts YCCK image to CMYK. YCCK is an equivalent encoding for
// CMYK data, so no color management code is needed here, nor does the
// PDF color space have to be consulted
private WritableRaster fromYCCKtoCMYK(Raster raster)
{
WritableRaster writableRaster = raster.createCompatibleWritableRaster();
int[] value = new int[4];
for (int y = 0, height = raster.getHeight(); y < height; y++)
{
for (int x = 0, width = raster.getWidth(); x < width; x++)
{
raster.getPixel(x, y, value);
// 4-channels 0..255
float Y = value[0];
float Cb = value[1];
float Cr = value[2];
float K = value[3];
// YCCK to RGB, see http://software.intel.com/en-us/node/442744
int r = clamp(Y + 1.402f * Cr - 179.456f);
int g = clamp(Y - 0.34414f * Cb - 0.71414f * Cr + 135.45984f);
int b = clamp(Y + 1.772f * Cb - 226.816f);
// naive RGB to CMYK
int cyan = 255 - r;
int magenta = 255 - g;
int yellow = 255 - b;
// update new raster
value[0] = cyan;
value[1] = magenta;
value[2] = yellow;
value[3] = (int)K;
writableRaster.setPixel(x, y, value);
}
}
return writableRaster;
}
private WritableRaster fromYCbCrtoCMYK(Raster raster)
{
WritableRaster writableRaster = raster.createCompatibleWritableRaster();
int[] value = new int[4];
for (int y = 0, height = raster.getHeight(); y < height; y++)
{
for (int x = 0, width = raster.getWidth(); x < width; x++)
{
raster.getPixel(x, y, value);
// 4-channels 0..255
float Y = value[0];
float Cb = value[1];
float Cr = value[2];
float K = value[3];
// YCbCr to RGB, see http://www.equasys.de/colorconversion.html
int r = clamp( (1.164f * (Y-16)) + (1.596f * (Cr - 128)) );
int g = clamp( (1.164f * (Y-16)) + (-0.392f * (Cb-128)) + (-0.813f * (Cr-128)));
int b = clamp( (1.164f * (Y-16)) + (2.017f * (Cb-128)));
// naive RGB to CMYK
int cyan = 255 - r;
int magenta = 255 - g;
int yellow = 255 - b;
// update new raster
value[0] = cyan;
value[1] = magenta;
value[2] = yellow;
value[3] = (int)K;
writableRaster.setPixel(x, y, value);
}
}
return writableRaster;
}
// converts from BGR to RGB
private WritableRaster fromBGRtoRGB(Raster raster)
{
WritableRaster writableRaster = raster.createCompatibleWritableRaster();
int width = raster.getWidth();
int height = raster.getHeight();
int w3 = width * 3;
int[] tab = new int[w3];
//BEWARE: handling the full image at a time is slower than one line at a time
for (int y = 0; y < height; y++)
{
raster.getPixels(0, y, width, 1, tab);
for (int off = 0; off < w3; off += 3)
{
int tmp = tab[off];
tab[off] = tab[off + 2];
tab[off + 2] = tmp;
}
writableRaster.setPixels(0, y, width, 1, tab);
}
return writableRaster;
}
// returns the number of channels as a string, or an empty string if there is an error getting the meta data
private String getNumChannels(ImageReader reader)
{
try
{
IIOMetadata imageMetadata = reader.getImageMetadata(0);
if (imageMetadata == null)
{
return "";
}
IIOMetadataNode metaTree = (IIOMetadataNode) imageMetadata.getAsTree("javax_imageio_1.0");
Element numChannelsItem = (Element) metaTree.getElementsByTagName("NumChannels").item(0);
if (numChannelsItem == null)
{
return "";
}
return numChannelsItem.getAttribute("value");
}
catch (IOException e)
{
return "";
}
catch (NegativeArraySizeException e)
{
return "";
}
}
// clamps value to 0-255 range
private int clamp(float value)
{
return (int)((value < 0) ? 0 : ((value > 255) ? 255 : value));
}
@Override
protected void encode(InputStream input, OutputStream encoded, COSDictionary parameters)
throws IOException
{
throw new UnsupportedOperationException("DCTFilter encoding not implemented, use the JPEGFactory methods instead");
}
}