No compression. The image data stored as raw bytes in RGBA planar order. That means that first all R data is written, then all G is written, then all B and finally all A data is written.
Rle
public static final PsdCompressionMethod Rle
RLE compressed. The image data starts with the byte counts for all the scan lines (rows * channels), with each count stored as a two-byte value. The RLE compressed data follows, with each scan line compressed separately. The RLE compression is the same compression algorithm used by the Macintosh ROM routine PackBits and the TIFF standard.
ZipWithoutPrediction
public static final PsdCompressionMethod ZipWithoutPrediction
ZIP without prediction.
ZipWithPrediction
public static final PsdCompressionMethod ZipWithPrediction