jdk中解析BMP图片的过程
在com.sun.imageio.plugins.bmp包中的BMPImageReader类中
public void readHeader() throws IOException {
if (gotHeader)
return;
if (iis == null) {
throw new IllegalStateException("Input source not set!");
}
int profileData = 0, profileSize = 0;
this.metadata = new BMPMetadata();
iis.mark();
// read and check the magic marker
byte[] marker = new byte[2];
iis.read(marker);
if (marker[0] != 0x42 || marker[1] != 0x4d)
throw new IllegalArgumentException(I18N.getString("BMPImageReader1"));
// Read file size
bitmapFileSize = iis.readUnsignedInt();
// skip the two reserved fields
iis.skipBytes(4);
// Offset to the bitmap from the beginning
bitmapOffset = iis.readUnsignedInt();
// End File Header
// Start BitmapCoreHeader
long size = iis.readUnsignedInt();
if (size == 12) {
width = iis.readShort();
height = iis.readShort();
} else {
width = iis.readInt();
height = iis.readInt();
}
metadata.width = width;
metadata.height = height;
int planes = iis.readUnsignedShort();
bitsPerPixel = iis.readUnsignedShort();
//metadata.colorPlane = planes;
metadata.bitsPerPixel = (short)bitsPerPixel;
// As BMP always has 3 rgb bands, except for Version 5,
// which is bgra
numBands = 3;
if (size == 12) {
// Windows 2.x and OS/2 1.x
metadata.bmpVersion = VERSION_2;
// Classify the image type
if (bitsPerPixel == 1) {
imageType = VERSION_2_1_BIT;
} else if (bitsPerPixel == 4) {
imageType = VERSION_2_4_BIT;
} else if (bitsPerPixel == 8) {
imageType = VERSION_2_8_BIT;
} else if (bitsPerPixel == 24) {
imageType = VERSION_2_24_BIT;
}
// Read in the palette
int numberOfEntries = (int)((bitmapOffset - 14 - size) / 3);
int sizeOfPalette = numberOfEntries*3;
palette = new byte[sizeOfPalette];
iis.readFully(palette, 0, sizeOfPalette);
metadata.palette = palette;
metadata.paletteSize = numberOfEntries;
} else {
compression = iis.readUnsignedInt();
imageSize = iis.readUnsignedInt();
long xPelsPerMeter = iis.readInt();
long yPelsPerMeter = iis.readInt();
long colorsUsed = iis.readUnsignedInt();
long colorsImportant = iis.readUnsignedInt();
metadata.compression = (int)compression;
metadata.xPixelsPerMeter = (int)xPelsPerMeter;
metadata.yPixelsPerMeter = (int)yPelsPerMeter;
metadata.colorsUsed = (int)colorsUsed;
metadata.colorsImportant = (int)colorsImportant;
if (size == 40) {
// Windows 3.x and Windows NT
switch((int)compression) {
case BI_JPEG:
case BI_PNG:
metadata.bmpVersion = VERSION_3;
imageType = VERSION_3_XP_EMBEDDED;
break;
case BI_RGB: // No compression
case BI_RLE8: // 8-bit RLE compression
case BI_RLE4: // 4-bit RLE compression
// Read in the palette
int numberOfEntries = (int)((bitmapOffset-14-size) / 4);
int sizeOfPalette = numberOfEntries * 4;
palette = new byte[sizeOfPalette];
iis.readFully(palette, 0, sizeOfPalette);
metadata.palette = palette;
metadata.paletteSize = numberOfEntries;
if (bitsPerPixel == 1) {
imageType = VERSION_3_1_BIT;
} else if (bitsPerPixel == 4) {
imageType = VERSION_3_4_BIT;
} else if (bitsPerPixel == 8) {
imageType = VERSION_3_8_BIT;
} else if (bitsPerPixel == 24) {
imageType = VERSION_3_24_BIT;
} else if (bitsPerPixel == 16) {
imageType = VERSION_3_NT_16_BIT;
redMask = 0x7C00;
greenMask = 0x3E0;
blueMask = (1 << 5) - 1;// 0x1F;
metadata.redMask = redMask;
metadata.greenMask = greenMask;
metadata.blueMask = blueMask;
} else if (bitsPerPixel == 32) {
imageType = VERSION_3_NT_32_BIT;
redMask = 0x00FF0000;
greenMask = 0x0000FF00;
blueMask = 0x000000FF;
metadata.redMask = redMask;
metadata.greenMask = greenMask;
metadata.blueMask = blueMask;
}
metadata.bmpVersion = VERSION_3;
break;
case BI_BITFIELDS:
if (bitsPerPixel == 16) {
imageType = VERSION_3_NT_16_BIT;
} else if (bitsPerPixel == 32) {
imageType = VERSION_3_NT_32_BIT;
}
// BitsField encoding
redMask = (int)iis.readUnsignedInt();
greenMask = (int)iis.readUnsignedInt();
blueMask = (int)iis.readUnsignedInt();
metadata.redMask = redMask;
metadata.greenMask = greenMask;
metadata.blueMask = blueMask;
if (colorsUsed != 0) {
// there is a palette
sizeOfPalette = (int)colorsUsed*4;
palette = new byte[sizeOfPalette];
iis.readFully(palette, 0, sizeOfPalette);
metadata.palette = palette;
metadata.paletteSize = (int)colorsUsed;
}
metadata.bmpVersion = VERSION_3_NT;
break;
default:
throw new
RuntimeException(I18N.getString("BMPImageReader2"));
}
} else if (size == 108 || size == 124) {
// Windows 4.x BMP
if (size == 108)
metadata.bmpVersion = VERSION_4;
else if (size == 124)
metadata.bmpVersion = VERSION_5;
// rgb masks, valid only if comp is BI_BITFIELDS
redMask = (int)iis.readUnsignedInt();
greenMask = (int)iis.readUnsignedInt();
blueMask = (int)iis.readUnsignedInt();
// Only supported for 32bpp BI_RGB argb
alphaMask = (int)iis.readUnsignedInt();
long csType = iis.readUnsignedInt();
int redX = iis.readInt();
int redY = iis.readInt();
int redZ = iis.readInt();
int greenX = iis.readInt();
int greenY = iis.readInt();
int greenZ = iis.readInt();
int blueX = iis.readInt();
int blueY = iis.readInt();
int blueZ = iis.readInt();
long gammaRed = iis.readUnsignedInt();
long gammaGreen = iis.readUnsignedInt();
long gammaBlue = iis.readUnsignedInt();
if (size == 124) {
metadata.intent = iis.readInt();
profileData = iis.readInt();
profileSize = iis.readInt();
iis.skipBytes(4);
}
metadata.colorSpace = (int)csType;
if (csType == LCS_CALIBRATED_RGB) {
// All the new fields are valid only for this case
metadata.redX = redX;
metadata.redY = redY;
metadata.redZ = redZ;
metadata.greenX = greenX;
metadata.greenY = greenY;
metadata.greenZ = greenZ;
metadata.blueX = blueX;
metadata.blueY = blueY;
metadata.blueZ = blueZ;
metadata.gammaRed = (int)gammaRed;
metadata.gammaGreen = (int)gammaGreen;
metadata.gammaBlue = (int)gammaBlue;
}
// Read in the palette
int numberOfEntries = (int)((bitmapOffset-14-size) / 4);
int sizeOfPalette = numberOfEntries*4;
palette = new byte[sizeOfPalette];
iis.readFully(palette, 0, sizeOfPalette);
metadata.palette = palette;
metadata.paletteSize = numberOfEntries;
switch ((int)compression) {
case BI_JPEG:
case BI_PNG:
if (size == 108) {
imageType = VERSION_4_XP_EMBEDDED;
} else if (size == 124) {
imageType = VERSION_5_XP_EMBEDDED;
}
break;
default:
if (bitsPerPixel == 1) {
imageType = VERSION_4_1_BIT;
} else if (bitsPerPixel == 4) {
imageType = VERSION_4_4_BIT;
} else if (bitsPerPixel == 8) {
imageType = VERSION_4_8_BIT;
} else if (bitsPerPixel == 16) {
imageType = VERSION_4_16_BIT;
if ((int)compression == BI_RGB) {
redMask = 0x7C00;
greenMask = 0x3E0;
blueMask = 0x1F;
}
} else if (bitsPerPixel == 24) {
imageType = VERSION_4_24_BIT;
} else if (bitsPerPixel == 32) {
imageType = VERSION_4_32_BIT;
if ((int)compression == BI_RGB) {
redMask = 0x00FF0000;
greenMask = 0x0000FF00;
blueMask = 0x000000FF;
}
}
metadata.redMask = redMask;
metadata.greenMask = greenMask;
metadata.blueMask = blueMask;
metadata.alphaMask = alphaMask;
}
} else {
throw new
RuntimeException(I18N.getString("BMPImageReader3"));
}
}
if (height > 0) {
// bottom up image
isBottomUp = true;
} else {
// top down image
isBottomUp = false;
height = Math.abs(height);
}
// Reset Image Layout so there's only one tile.
//Define the color space
ColorSpace colorSpace = ColorSpace.getInstance(ColorSpace.CS_sRGB);
if (metadata.colorSpace == PROFILE_LINKED ||
metadata.colorSpace == PROFILE_EMBEDDED) {
iis.mark();
iis.skipBytes(profileData - size);
byte[] profile = new byte[profileSize];
iis.readFully(profile, 0, profileSize);
iis.reset();
try {
if (metadata.colorSpace == PROFILE_LINKED)
colorSpace =
new ICC_ColorSpace(ICC_Profile.getInstance(new String(profile)));
else
colorSpace =
new ICC_ColorSpace(ICC_Profile.getInstance(profile));
} catch (Exception e) {
colorSpace = ColorSpace.getInstance(ColorSpace.CS_sRGB);
}
}
if (bitsPerPixel == 0 ||
compression == BI_JPEG || compression == BI_PNG )
{
// the colorModel and sampleModel will be initialzed
// by the reader of embedded image
colorModel = null;
sampleModel = null;
} else if (bitsPerPixel == 1 || bitsPerPixel == 4 || bitsPerPixel == 8) {
// When number of bitsPerPixel is <= 8, we use IndexColorModel.
numBands = 1;
if (bitsPerPixel == 8) {
int[] bandOffsets = new int[numBands];
for (int i = 0; i < numBands; i++) {
bandOffsets[i] = numBands -1 -i;
}
sampleModel =
new PixelInterleavedSampleModel(DataBuffer.TYPE_BYTE,
width, height,
numBands,
numBands * width,
bandOffsets);
} else {
// 1 and 4 bit pixels can be stored in a packed format.
sampleModel =
new MultiPixelPackedSampleModel(DataBuffer.TYPE_BYTE,
width, height,
bitsPerPixel);
}
// Create IndexColorModel from the palette.
byte r[], g[], b[];
if (imageType == VERSION_2_1_BIT ||
imageType == VERSION_2_4_BIT ||
imageType == VERSION_2_8_BIT) {
size = palette.length/3;
if (size > 256) {
size = 256;
}
int off;
r = new byte[(int)size];
g = new byte[(int)size];
b = new byte[(int)size];
for (int i=0; i<(int)size; i++) {
off = 3 * i;
b[i] = palette[off];
g[i] = palette[off+1];
r[i] = palette[off+2];
}
} else {
size = palette.length/4;
if (size > 256) {
size = 256;
}
int off;
r = new byte[(int)size];
g = new byte[(int)size];
b = new byte[(int)size];
for (int i=0; i<size; i++) {
off = 4 * i;
b[i] = palette[off];
g[i] = palette[off+1];
r[i] = palette[off+2];
}
}
if (ImageUtil.isIndicesForGrayscale(r, g, b))
colorModel =
ImageUtil.createColorModel(null, sampleModel);
else
colorModel = new IndexColorModel(bitsPerPixel, (int)size, r, g, b);
} else if (bitsPerPixel == 16) {
numBands = 3;
sampleModel =
new SinglePixelPackedSampleModel(DataBuffer.TYPE_USHORT,
width, height,
new int[] {redMask, greenMask, blueMask});
colorModel =
new DirectColorModel(colorSpace,
16, redMask, greenMask, blueMask, 0,
false, DataBuffer.TYPE_USHORT);
} else if (bitsPerPixel == 32) {
numBands = alphaMask == 0 ? 3 : 4;
// The number of bands in the SampleModel is determined by
// the length of the mask array passed in.
int[] bitMasks = numBands == 3 ?
new int[] {redMask, greenMask, blueMask} :
new int[] {redMask, greenMask, blueMask, alphaMask};
sampleModel =
new SinglePixelPackedSampleModel(DataBuffer.TYPE_INT,
width, height,
bitMasks);
colorModel =
new DirectColorModel(colorSpace,
32, redMask, greenMask, blueMask, alphaMask,
false, DataBuffer.TYPE_INT);
} else {
numBands = 3;
// Create SampleModel
int[] bandOffsets = new int[numBands];
for (int i = 0; i < numBands; i++) {
bandOffsets[i] = numBands -1 -i;
}
sampleModel =
new PixelInterleavedSampleModel(DataBuffer.TYPE_BYTE,
width, height,
numBands,
numBands * width,
bandOffsets);
colorModel =
ImageUtil.createColorModel(colorSpace, sampleModel);
}
originalSampleModel = sampleModel;
originalColorModel = colorModel;
// Reset to the start of bitmap; then jump to the
//start of image data
iis.reset();
iis.skipBytes(bitmapOffset);
gotHeader = true;
}
public BufferedImage read(int imageIndex, ImageReadParam param)
throws IOException {
if (iis == null) {
throw new IllegalStateException(I18N.getString("BMPImageReader5"));
}
checkIndex(imageIndex);
clearAbortRequest();
processImageStarted(imageIndex);
if (param == null)
param = getDefaultReadParam();
//read header
readHeader();
sourceRegion = new Rectangle(0, 0, 0, 0);
destinationRegion = new Rectangle(0, 0, 0, 0);
computeRegions(param, this.width, this.height,
param.getDestination(),
sourceRegion,
destinationRegion);
scaleX = param.getSourceXSubsampling();
scaleY = param.getSourceYSubsampling();
// If the destination band is set used it
sourceBands = param.getSourceBands();
destBands = param.getDestinationBands();
seleBand = (sourceBands != null) && (destBands != null);
noTransform =
destinationRegion.equals(new Rectangle(0, 0, width, height)) ||
seleBand;
if (!seleBand) {
sourceBands = new int[numBands];
destBands = new int[numBands];
for (int i = 0; i < numBands; i++)
destBands[i] = sourceBands[i] = i;
}
// If the destination is provided, then use it. Otherwise, create new one
bi = param.getDestination();
// Get the image data.
WritableRaster raster = null;
if (bi == null) {
if (sampleModel != null && colorModel != null) {
sampleModel =
sampleModel.createCompatibleSampleModel(destinationRegion.x +
destinationRegion.width,
destinationRegion.y +
destinationRegion.height);
if (seleBand)
sampleModel = sampleModel.createSubsetSampleModel(sourceBands);
raster = Raster.createWritableRaster(sampleModel, new Point());
bi = new BufferedImage(colorModel, raster, false, null);
}
} else {
raster = bi.getWritableTile(0, 0);
sampleModel = bi.getSampleModel();
colorModel = bi.getColorModel();
noTransform &= destinationRegion.equals(raster.getBounds());
}
byte bdata[] = null; // buffer for byte data
short sdata[] = null; // buffer for short data
int idata[] = null; // buffer for int data
// the sampleModel can be null in case of embedded image
if (sampleModel != null) {
if (sampleModel.getDataType() == DataBuffer.TYPE_BYTE)
bdata = (byte[])
((DataBufferByte)raster.getDataBuffer()).getData();
else if (sampleModel.getDataType() == DataBuffer.TYPE_USHORT)
sdata = (short[])
((DataBufferUShort)raster.getDataBuffer()).getData();
else if (sampleModel.getDataType() == DataBuffer.TYPE_INT)
idata = (int[])
((DataBufferInt)raster.getDataBuffer()).getData();
}
// There should only be one tile.
switch(imageType) {
case VERSION_2_1_BIT:
// no compression
read1Bit(bdata);
break;
case VERSION_2_4_BIT:
// no compression
read4Bit(bdata);
break;
case VERSION_2_8_BIT:
// no compression
read8Bit(bdata);
break;
case VERSION_2_24_BIT:
// no compression
read24Bit(bdata);
break;
case VERSION_3_1_BIT:
// 1-bit images cannot be compressed.
read1Bit(bdata);
break;
case VERSION_3_4_BIT:
switch((int)compression) {
case BI_RGB:
read4Bit(bdata);
break;
case BI_RLE4:
readRLE4(bdata);
break;
default:
throw new
RuntimeException(I18N.getString("BMPImageReader1"));
}
break;
case VERSION_3_8_BIT:
switch((int)compression) {
case BI_RGB:
read8Bit(bdata);
break;
case BI_RLE8:
readRLE8(bdata);
break;
default:
throw new
RuntimeException(I18N.getString("BMPImageReader1"));
}
break;
case VERSION_3_24_BIT:
// 24-bit images are not compressed
read24Bit(bdata);
break;
case VERSION_3_NT_16_BIT:
read16Bit(sdata);
break;
case VERSION_3_NT_32_BIT:
read32Bit(idata);
break;
case VERSION_3_XP_EMBEDDED:
case VERSION_4_XP_EMBEDDED:
case VERSION_5_XP_EMBEDDED:
bi = readEmbedded((int)compression, bi, param);
break;
case VERSION_4_1_BIT:
read1Bit(bdata);
break;
case VERSION_4_4_BIT:
switch((int)compression) {
case BI_RGB:
read4Bit(bdata);
break;
case BI_RLE4:
readRLE4(bdata);
break;
default:
throw new
RuntimeException(I18N.getString("BMPImageReader1"));
}
case VERSION_4_8_BIT:
switch((int)compression) {
case BI_RGB:
read8Bit(bdata);
break;
case BI_RLE8:
readRLE8(bdata);
break;
default:
throw new
RuntimeException(I18N.getString("BMPImageReader1"));
}
break;
case VERSION_4_16_BIT:
read16Bit(sdata);
break;
case VERSION_4_24_BIT:
read24Bit(bdata);
break;
case VERSION_4_32_BIT:
read32Bit(idata);
break;
}
if (abortRequested())
processReadAborted();
else
processImageComplete();
return bi;
}当然这里还有对gif，jpg，bmp等常用图片的解析，有兴趣的可以去看下。
