com.sun.image.codec.jpeg classes. Users needing that additional functionality should use those classes directly, bearing in mind that they are part of an uncommitted non-core interface that may be modified or removed in the future. This class makes very simple assumptions about the image colorspaces. Images with a single band are assumed to be grayscale. Images with three bands are assumed to be RGB and are encoded to YCbCr. This class is not a committed part of the JAI API. It may be removed or changed in future releases of JAI.
When working with BufferedImages, the codec will attempt to match the encoded JPEG COLOR_ID with the ColorModel in the BufferedImage. This is not always possible (the default mappings are listed below). In cases where unsupported conversions are required (or odd image colorspaces are in use) the user must either convert the image data to a known ColorSpace or encode the data from a raster. When encoding rasters no colorspace adjustments are made, so the user must do any conversions required to get to the encoded COLOR_ID. The COLOR_ID for the encoded images is used to control the JPEG codec's inital values for Huffman and Quantization Tables as well as subsampling factors. It is also used to determine what color conversion should be performed to obtain the best encoding.
Note: The color ids described herein are simply enumerated values that influence data processing by the JPEG codec. JPEG compression is, by definition, color blind. These values are used as hints when compressing JPEG data. Through these values the JPEG codec can perform some default rotation of data into spaces that will aid in getting better compression ratios.
Example behaviour is described below. Since these mappings are likely to change in the future it is strongly recommended that you make use of the @see JPEGImageEncoder.getDefaultParamBlock calls and check the encodedColorID for your particular BufferedImage. In extreme cases is may be necessary for the user to convert the image to the desired colorspace, and encode it from a Raster. In this case the API programmer must specify the colorID of the data in the Raster and no color conversion will take place.
ENCODING: BufferedImage Type/Instance JPEG (Encoded) Color ID ======================== ======================= TYPE_GRAY COLOR_ID_GRAYSCALE TYPE_RGB COLOR_ID_YCbCr TYPE_YCbCr COLOR_ID_YCbCr TYPE_YCbCr/CS_PYCC COLOR_ID_PYCC TYPE_CMYK COLOR_ID_CMYK TYPE_RGB (w/ alpha) COLOR_ID_YCbCrA TYPE_YCbCr (w/ alpha) COLOR_ID_YCbCrA TYPE_YCbCr/CS_PYCC (w/ alpha) COLOR_ID_PYCCA Any Other ** COLOR_ID_UNKNOWNWhen the user wants more control than the BufferedImage conversions provide, the user must encode the data from a Raster. In this case the data undergoes no color conversion at all. It is the user's responsiblity to perform the desired conversions.
If you intend to write a JFIF image (by including the APP0_MARKER) the encoded COLOR_ID must be one of: COLOR_ID_UNKNOWN, COLOR_ID_GRAYSCALE, COLOR_ID_YCbCr, or COLOR_ID_CMYK. In all other instances an ImageformatException will be thrown.
IMPORTANT: an Alpha RGB BufferedImage will not map to a valid JFIF stream, you must strip off the alpha prior to encoding if you want a JFIF file. If the APP0 marker is set and you do not strip off the Alpha, an ImageFormatException will be thrown.
Note that the classes in the com.sun.image.codec.jpeg package are not part of the core Java APIs. They are a part of Sun's JDK and JRE distributions. Although other licensees may choose to distribute these classes, developers cannot depend on their availability in non-Sun implementations. We expect that equivalent functionality will eventually be available in a core API or standard extension.
com.sun.image.codec.jpeg classes. Users needing that additional functionality should use those classes directly, bearing in mind that they are part of an uncommitted non-core interface that may be modified or removed in the future. This class makes very simple assumptions about the image colorspaces. Images with a single band are assumed to be grayscale. Images with three bands are assumed to be RGB and are encoded to YCbCr. This class is not a committed part of the JAI API. It may be removed or changed in future releases of JAI.
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