forked from mirror/libbpg
libbpg-0.9.4
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11 changed files with 811 additions and 388 deletions
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@ -1,6 +1,6 @@
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BPG Specification
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version 0.9.3
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version 0.9.4
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Copyright (c) 2014 Fabrice Bellard
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@ -17,8 +17,12 @@ space is either BT 601 (JPEG case), BT 709 or BT 2020.
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The chroma can be subsampled by a factor of two in horizontal or both
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in horizontal and vertical directions (4:4:4, 4:2:2 or 4:2:0 chroma
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formats are supported). The chroma is sampled at the same position
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relative to the luma as in the JPEG format [2].
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formats are supported). In order to be able to transcode JPEG images
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or video frames without modification to the chroma, both JPEG and
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MPEG2 chroma sample positions are supported.
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Progressive decoding and display is supported by interleaving the
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alpha and color data.
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Arbitrary metadata (such as EXIF, ICC profile, XMP) are supported.
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@ -73,24 +77,17 @@ heic_file() {
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picture_data_length ue7(32)
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if (extension_present_flag)
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extension_data_length ue7(32)
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if (alpha1_flag || alpha2_flag)
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alpha_data_length ue7(32)
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if (extension_present_flag) {
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extension_data()
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}
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hevc_header_and_data()
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if (alpha1_flag || alpha2_flag) {
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hevc_header_and_data()
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}
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}
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extension_data()
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{
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for(i = 0; i < v; i++) {
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while (more_bytes()) {
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extension_tag ue7(32)
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extension_tag_length ue7(32)
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for(j = 0; j < extension_tag_length; j++) {
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@ -100,6 +97,15 @@ extension_data()
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}
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hevc_header_and_data()
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{
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if (alpha1_flag || alpha2_flag) {
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hevc_header()
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}
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hevc_header()
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hevc_data()
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}
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hevc_header()
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{
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hevc_header_length ue7(32)
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log2_min_luma_coding_block_size_minus3 ue(v)
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@ -134,8 +140,6 @@ hevc_header_and_data()
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cabac_bypass_alignment_enabled_flag u(1)
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}
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trailing_bits u(v)
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hevc_data()
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}
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hevc_data()
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@ -154,9 +158,11 @@ hevc_data()
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'pixel_format' indicates the chroma subsampling:
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0 : Grayscale
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1 : 4:2:0
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2 : 4:2:2
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1 : 4:2:0. Chroma at position (0.5, 0.5) (JPEG chroma position)
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2 : 4:2:2. Chroma at position (0.5, 0) (JPEG chroma position)
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3 : 4:4:4
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4 : 4:2:0. Chroma at position (0, 0.5) (MPEG2 chroma position)
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5 : 4:2:2. Chroma at position (0, 0) (MPEG2 chroma position)
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The other values are reserved.
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@ -217,9 +223,8 @@ hevc_data()
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For RGB, G is stored as the Y plane. B in the Cb plane and R in
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the Cr plane.
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YCgCo is defined as HEVC matrix_coeffs = 8, full range. Y is
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stored in the Y plane. Cg in the Cb plane and Co in the Cr
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plane.
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YCgCo is defined as HEVC matrix_coeffs = 8. Y is stored in the
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Y plane. Cg in the Cb plane and Co in the Cr plane.
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If no color profile is present, the RGB output data are assumed
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to be in the sRGB color space [6].
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@ -246,12 +251,12 @@ hevc_data()
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'picture_height' is the picture height in pixels. The value 0 is
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not allowed.
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'picture_data_length' is the picture data length in bytes.
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'picture_data_length' is the picture data length in bytes. The
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special value of zero indicates that the picture data goes up to
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the end of the file.
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'extension_data_length' is the extension data length in bytes.
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'alpha_data_length' is the alpha data length in bytes.
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'extension_data()' is the extension data.
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'extension_tag' is the extension tag. The following values are defined:
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@ -320,7 +325,19 @@ hevc_data()
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- bit_depth_luma_minus8 = bit_depth_minus_8
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- bit_depth_chroma_minus8 = bit_depth_minus_8
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- scaling_list_enabled_flag = 0
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Alpha data encoding:
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- If alpha data is present, all the corresponding NALs have
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nuh_layer_id = 1. NALs for color data shall have nuh_layer_id =
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0.
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- Alpha data shall use the same tile sizes as color data and
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shall have the same entropy_coding_sync_enabled_flag value as
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color data.
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- Alpha slices shall use the same number of coding units as color
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slices and should be interleaved with color slices. alpha NALs
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shall come before the corresponding color NALs.
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3.3) HEVC Profile
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-----------------
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@ -361,7 +378,7 @@ information.
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- Pixel formats: we wanted to be able to convert JPEG images to BPG
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with as little loss as possible. So supporting the same color space
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(CCIR 601 YCbCr) with the same range (full range) and most of the
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(BT 601 YCbCr) with the same range (full range) and most of the
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allowed JPEG chroma formats (4:4:4, 4:2:2, 4:2:0 or grayscale) was
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mandatory to avoid going back to RGB or doing a subsampling or
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interpolation.
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@ -371,7 +388,14 @@ information.
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format to simplify the decoder. The color is either
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non-premultiplied or premultiplied. Premultiplied alpha usually
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gives a better compression. Non-premultiplied alpha is supported in
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case no loss is needed on the color components.
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case no loss is needed on the color components. In order to allow
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progressive display, the alpha and color data are interleaved (the
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nuh_layed_id NAL field is 0 for color data and 1 for alpha
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data). The alpha and color slices should contain the same number of
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coding units and each alpha slice should come before the
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corresponding color slice. Since alpha slices are usually smaller
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than color slices, it allows a progressive display even if there is
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a single slice.
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- Color spaces: In addition to YCbCr, RGB is supported for the high
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quality or lossless cases. YCgCo is supported because it may give
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@ -423,4 +447,4 @@ information.
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[5] Extensible Metadata Platform (XMP) http://www.adobe.com/devnet/xmp.html
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[6] sRGB color space, IEC 61966-2-1.
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[6] sRGB color space, IEC 61966-2-1
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