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Clean up and consolidate notes regarding the YUV image format. This also corrects a factual error regarding the padding of the luminance plane-- because we now support 4:1:1, the component width is not necessarily padded to the nearest multiple of 2 if horizontal subsampling is used.

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git-svn-id: svn+ssh://svn.code.sf.net/p/libjpeg-turbo/code/trunk@1342 632fc199-4ca6-4c93-a231-07263d6284db
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DRC
2014-08-10 20:12:17 +00:00
parent 779bd68d20
commit 493be61707
6 changed files with 140 additions and 102 deletions
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50
java/org/libjpegturbo/turbojpeg/YUVImage.java
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@@ -29,7 +29,7 @@
package org.libjpegturbo.turbojpeg;
/**
* This class encapsulates a YUV planar image buffer and the metadata
* This class encapsulates a YUV planar image and the metadata
* associated with it. The TurboJPEG API allows both the JPEG compression and
* decompression pipelines to be split into stages: YUV encode, compress from
* YUV, decompress to YUV, and YUV decode. A <code>YUVImage</code> instance
@@ -40,18 +40,28 @@ package org.libjpegturbo.turbojpeg;
* Technically, the JPEG format uses the YCbCr colorspace (which technically is
* not a "colorspace" but rather a "color transform"), but per the convention
* of the digital video community, the TurboJPEG API uses "YUV" to refer to an
* image format consisting of Y, Cb, and Cr image planes. In this image
* format, the Y, Cb (U), and Cr (V) planes are stored sequentially in the same
* image buffer, and the size of each plane is determined by the image width,
* height, line padding, and level of chrominance subsampling. If the
* chrominance components are subsampled along the horizontal dimension, then
* the width of the luminance plane would be padded to the nearest multiple of
* 2 (same goes for the height of the luminance plane, if the chrominance
* components are subsampled along the vertical dimension.) For instance, if
* the source image is 35 x 35 pixels and 4:2:2 subsampling is used, then the
* luminance plane would be 36 x 35 bytes, and each of the chrominance planes
* would be 18 x 35 bytes. If you specify, for instance, a line padding of 4
* bytes on top of this, then the luminance plane would be 36 x 35 bytes, and
* image format consisting of Y, Cb, and Cr image planes.
* <p>
* Each plane is simply a 2D array of bytes, each byte representing the value
* of one of the components at a particular location in the image. The
* "component width" and "component height" of each plane are determined by the
* image width, height, and level of chrominance subsampling. For the
* luminance plane, the component width is the image width padded to the
* nearest multiple of the horizontal subsampling factor (2 in the case of
* 4:2:0 and 4:2:2, 4 in the case of 4:1:1, 1 in the case of 4:4:4 or
* grayscale.) Similarly, the component height of the luminance plane is the
* image height padded to the nearest multiple of the vertical subsampling
* factor (2 in the case of 4:2:0 or 4:4:0, 1 in the case of 4:4:4 or
* grayscale.) The component width of the chrominance planes is equal to the
* component width of the luminance plane divided by the horizontal subsampling
* factor, and the component height of the chrominance planes is equal to the
* component height of the luminance plane divided by the vertical subsampling
* factor.
* <p>
* For example, if the source image is 35 x 35 pixels and 4:2:2 subsampling is
* used, then the luminance plane would be 36 x 35 bytes, and each of the
* chrominance planes would be 18 x 35 bytes. If you specify a line padding of
* 4 bytes on top of this, then the luminance plane would be 36 x 35 bytes, and
* each of the chrominance planes would be 20 x 35 bytes.
*/
public class YUVImage {
@@ -83,9 +93,10 @@ public class YUVImage {
* buffer.
*
* @param yuvImage image buffer that contains or will contain YUV planar
* image data. See {@link YUVImage above} for a description of the image
* format. Use {@link TJ#bufSizeYUV} to determine the minimum size for this
* buffer.
* image data. Use {@link TJ#bufSizeYUV} to determine the minimum size for
* this buffer. The Y, U (Cb), and V (Cr) image planes are stored
* sequentially in the buffer (see {@link YUVImage above} for a description
* of the image format.)
*
* @param width width (in pixels) of the YUV image
*
@@ -108,9 +119,10 @@ public class YUVImage {
* instance.
*
* @param yuvImage image buffer that contains or will contain YUV planar
* image data. See {@link YUVImage above} for a description of the image
* format. Use {@link TJ#bufSizeYUV} to determine the minimum size for this
* buffer.
* image data. Use {@link TJ#bufSizeYUV} to determine the minimum size for
* this buffer. The Y, U (Cb), and V (Cr) image planes are stored
* sequentially in the buffer (see {@link YUVImage above} for a description
* of the image format.)
*
* @param width width (in pixels) of the YUV image
*