YUV與RGB大致的轉換方式
R=Y+1.140*V
G=Y-0.395*U-0.581*V
B=Y+2.032*U
Y=+0.299*R+0.587*G+0.114*B
U=-0.147*R-0.289*G+0.436*B
V=+0.615*R-0.515*G-0.100*B
YUV is a class of pixel formats used in video applications, including VLC media player.
YUV is actually the name of the color space that is common to all "YUV" pixel formats. Contrary to RGB formats (Red-Green-Blue), YUV colors are represented with one "luminance" component called Y (equivalent to grey scale) and two "chrominance" components, called U (blue projection) and V (red projection) respectively, hence the name.
YUV can also be referred to as YCbCr, although the terms mean slightly different things,[note 1] they tend to be confused and used interchangeably (including in VLC-related venues).
This page explains the most useful YUV pixel formats in the context of VLC media player. Unless otherwise stated, values for each component are stored in one octet (8 bits).
Contents
Planar formats
Planar (or sometimes "triplanar") formats use separate matrices for each of the 3 color components. In other words, there is one table of luminance pixel values, and two separate tables for the chrominance components. This segregated representation in memory of pixels is more convenient for video coding.
YUV 4:2:0 (I420/J420/YV12)
I420
It has the luma "luminance" plane Y first, then the U chroma plane and last the V chroma plane.
The two chroma planes (blue and red projections) are sub-sampled in both the horizontal and vertical dimensions by a factor of 2. That is to say, for a 2×2 square of pixels, there are 4 Y samples but only 1 U sample and 1 V sample.
This format requires 4×8+8+8=48 bits per 4 pixels, so its depth is 12 bits per pixel.
I420 is by far the most common format in VLC. Most video decoders output raw pictures in I420 format.
A graphical illustration: Each letter represents one bit.
For a single I420 pixel: YYYYYYYY UU VV
For a 50-pixel I420 frame: YYYYYYYY×50 UU×50 VV×50 (or Y×8×50 U×2×50 V×2×50 for short)
For an n-pixel I420 frame: Y×8×n U×2×n V×2×n
J420
J420 is exactly like I420, but with a full range ("digital", 0-255) luma (Y) component instead of limited range ("analog", 16-240). The chroma planes are exactly the same as in I420.
YV12
YV12 is exactly like I420, but the order of the U and V planes is reversed. In the name, "YV" refers to the plane order: Y, then V (then U). "12" refers to the pixel depth: 12-bits per pixel as for I420.
YUV 4:2:2 (I422/J422)
I422
Like I420, I422 has one luma plane Y and 2 chroma planes U, V.
However, in I422, chroma planes (blue and red projections) are sub-sampled only in the horizontal dimension, still by a factor of 2. Thus, there is the same amount of lines in chroma planes as in the luma plane.
For a 2×2 group of pixels, there are 4 Y samples and 2 U and 2 V samples each. The depth is 4×8+2×8+2×8=64 bits per 4 pixels, so 16 bits per pixel.
Some video codecs support I422 (optionally) for higher quality video encoding.
J422
J422 is exactly like I422, but with a full range ("digital", 0-255) luma (Y) component instead of limited range ("analog", 16-240). The chroma planes are exactly the same as in I422.
YUV 4:4:4
I444
As I420 and I422, I444 has one luma plane Y and 2 chroma planes U and V. Chroma planes are not sub-sampled: there are 3 octet values for each pixels. The depth is thus 24 bits per pixel (as with RGB24 or RGB32).
A few video codecs support I444 optionally.
Packed formats
In packed formats, you usually have only one plane, with all the luma and chroma data interleaved. This is similar to RGB pixel formats, only using a different color space.
Packed formats are very popular inside webcams. In hardware, using separate planes is inefficient: several memory accesses are needed for each pixel. Packed formats are easier and thus cheaper to use.
On the other hand, packet formats cannot normally deal with vertical sub-sampling. Otherwise scan lines would have different sizes. So generally, packed formats are horizontally subsampled, especially by a factor of 2 (i.e., YUV 4:2:2).
UYVY
Known as UYVY, Y422 or UYNV.
In UYVY, the chroma samples are sub-sampled by a factor of 2.
In UYVY, the succession for 2 pixels, starts by U then one luma if the first pixel, then V and then another luma for the second pixel.
YUY2
Known as YUY2, YUYV, V422 or YUNV.
In YUY2, the chroma samples are sub-sampled by a factor of 2.
In YUY2, the succession for 2 pixels, starts by one luma for the first pixel, then U, then another luma for the second pixel and then V again.
Conversion between YUY2 and UYVY is achieved by swapping bytes pairwise.
YVYU
YVYU is just like YUY2, but with U and V order reversed.
VYUV
TBD.
Semi-planar
Semi planar formats have two planes instead of three, one plane for luminance, and one plane for both chrominance components. They are also sometimes referred to as biplanar formats also.
NV12/NV21
NV12
Related to I420, NV12 has one luma "luminance" plane Y and one plane with U and V values interleaved.
In NV12, chroma planes (blue and red) are subsampled in both the horizontal and vertical dimensions by a factor of 2.
For a 2×2 group of pixels, you have 4 Y samples and 1 U and 1 V sample.
It can be helpful to think of NV12 as I420 with the U and V planes interleaved.
Here is a graphical representation of NV12. Each letter represents one bit:
For 1 NV12 pixel: YYYYYYYY UVUV
For a 2-pixel NV12 frame: YYYYYYYYYYYYYYYY UVUVUVUV
For a 50-pixel NV12 frame: Y×8×50 (UV)×2×50
For a n-pixel NV12 frame: Y×8×n (UV)×2×n
NV21
NV21 is like NV12, but with U and V order reversed: it starts with V.
Other NV formats
Following the same pattern as NV12/NV21, there are NV16/NV61 (4:2:2 sub-sampling) and NV24/NV42 (4:4:4 sampling) formats. They are mostly used in some funky cheap camera circuitry and not supported in VLC (as of VLC version 2.0).
Notes
^ note 1 Technical details are generally understood from context. Everything described on this page is Y′CbCr, not Y′UV.
Y′CbCr chroma subsampling formats (e.g. 4:2:0) are used only for digital signals; VLC deals with digital signals.
In many cases: Y′UV is for analog signals, Y′PbPr for analog signals in video component cables; Y′CbCr for digital signals (including MPEG-2). Gamma correction is indicated by a prime ′, thus gamma-corrected YCbCr is written Y′CbCr. For an extended discussion see YUV and luminance considered harmful or Color FAQ § What are colour differences? by Charles Poynton
Further reading
https://fourcc.org/yuv.php
Packed YUV Formats
Label FOURCC in Hex Bits per pixel Description
AYUV 0x56555941 32 Combined YUV and alpha
CLJR 0x524A4C43 8 Cirrus Logic format with 4 pixels packed into a u_int32. A form of YUV 4:1:1 wiht less than 8 bits per Y, U and V sample.
CYUV 0x76757963 16 Essentially a copy of UYVY except that the sense of the height is reversed - the image is upside down with respect to the UYVY version.
GREY
(Y800) 0x59455247 8 Apparently a duplicate of Y800 (and also, presumably, "Y8 ")
HDYC
(UYVY) 0x43594448 16 YUV 4:2:2 (Y sample at every pixel, U and V sampled at every second pixel horizontally on each line). A macropixel contains 2 pixels in 1 u_int32. This is a suplicate of UYVY except that the color components use the BT709 color space (as used in HD video).
IRAW 0x57615349 ? Intel uncompressed YUV. I have no information on this format - can you help?
IUYV
(UYVY) 0x56595549 16 Interlaced version of UYVY (line order 0, 2, 4,....,1, 3, 5....) registered by Silviu Brinzei of LEAD Technologies.
IY41 0x31555949 12 Interlaced version of Y41P (line order 0, 2, 4,....,1, 3, 5....) registered by Silviu Brinzei of LEAD Technologies.
IYU1 0x31555949 12 12 bit format used in mode 2 of the IEEE 1394 Digital Camera 1.04 spec. This is equivalent to Y411
IYU2 0x32555949 24 24 bit format used in mode 0 of the IEEE 1394 Digital Camera 1.04 spec
UYNV
(UYVY) 0x564E5955 16 A direct copy of UYVY registered by NVidia to work around problems in some old codecs which did not like hardware which offered more than 2 UYVY surfaces.
UYVP 0x50565955 24? YCbCr 4:2:2 extended precision 10-bits per component in U0Y0V0Y1 order. Registered by Rich Ehlers of Evans & Sutherland.
UYVY 0x59565955 16 YUV 4:2:2 (Y sample at every pixel, U and V sampled at every second pixel horizontally on each line). A macropixel contains 2 pixels in 1 u_int32.
V210 0x30313256 32 10-bit 4:2:2 YCrCb equivalent to the Quicktime format of the same name.
V422 0x32323456 16 I am told that this is an upside down version of UYVY.
V655 0x35353656 16? 16 bit YUV 4:2:2 format registered by Vitec Multimedia. I have no information on the component ordering or packing.
VYUY 0x59555956 ? ATI Packed YUV Data (format unknown)
Y16 0x20363159 16 16-bit uncompressed greyscale image.
Y211 0x31313259 8 Packed YUV format with Y sampled at every second pixel across each line and U and V sampled at every fourth pixel.
Y411 0x31313459 12 YUV 4:1:1 with a packed, 6 byte/4 pixel macroblock structure.
Y41P 0x50313459 12 YUV 4:1:1 (Y sample at every pixel, U and V sampled at every fourth pixel horizontally on each line). A macropixel contains 8 pixels in 3 u_int32s.
Y41T 0x54313459 12 Format as for Y41P but the lsb of each Y component is used to signal pixel transparency .
Y422
(UYVY) 0x32323459 16 Direct copy of UYVY as used by ADS Technologies Pyro WebCam firewire camera.
Y42T 0x54323459 16 Format as for UYVY but the lsb of each Y component is used to signal pixel transparency .
Y8
(Y800) 0x20203859 8 Duplicate of Y800 as far as I can see.
Y800 0x30303859 8 Simple, single Y plane for monochrome images.
YUNV
(YUY2) 0x564E5559 16 A direct copy of YUY2 registered by NVidia to work around problems in some old codecs which did not like hardware which offered more than 2 YUY2 surfaces.
YUVP 0x50565559 24? YCbCr 4:2:2 extended precision 10-bits per component in Y0U0Y1V0 order. Registered by Rich Ehlers of Evans & Sutherland.
YUY2 0x32595559 16 YUV 4:2:2 as for UYVY but with different component ordering within the u_int32 macropixel.
YUYV
(YUY2) 0x56595559 16 Duplicate of YUY2
YVYU 0x55595659 16 YUV 4:2:2 as for UYVY but with different component ordering within the u_int32 macropixel.
Planar YUV Formats
Label FOURCC in Hex Bits per pixel Description
CLPL 0x4C504C43 12 Format similar to YV12 but including a level of indirection.
CXY1 0x31595843 12 Planar YUV 4:1:1 format registered by Conexant.
CXY2 0x32595842 16 Planar YUV 4:2:2 format registered by Conexant.
I420 0x30323449 12 8 bit Y plane followed by 8 bit 2x2 subsampled U and V planes.
IF09 0x39304649 9.5 As YVU9 but an additional 4x4 subsampled plane is appended containing delta information relative to the last frame. (Bpp is reported as 9)
IMC1 0x31434D49 12 As YV12 except the U and V planes each have the same stride as the Y plane
IMC2 0x32434D49 12 Similar to IMC1 except that the U and V lines are interleaved at half stride boundaries
IMC3
(IMC1) 0x33434D49 12 As IMC1 except that U and V are swapped
IMC4
(IMC2) 0x34434D49 12 As IMC2 except that U and V are swapped
IYUV
(I420) 0x56555949 12 Duplicate FOURCC, identical to I420.
NV12 0x3231564E 12 8-bit Y plane followed by an interleaved U/V plane with 2x2 subsampling
NV21 0x3132564E 12 As NV12 with U and V reversed in the interleaved plane
Y41B 0x42313459 12? Weitek format listed as "YUV 4:1:1 planar". I have no other information on this format.
Y42B 0x42323459 16? Weitek format listed as "YUV 4:2:2 planar". I have no other information on this format.
Y8
(Y800) 0x20203859 8 Duplicate of Y800 as far as I can see.
Y800 0x30303859 8 Simple, single Y plane for monochrome images.
YUV9 0x39565559 9? Registered by Intel., this is the format used internally by Indeo video code
YV12 0x32315659 12 8 bit Y plane followed by 8 bit 2x2 subsampled V and U planes.
YV16 0x36315659 16 8 bit Y plane followed by 8 bit 2x1 subsampled V and U planes.
YVU9 0x39555659 9 8 bit Y plane followed by 8 bit 4x4 subsampled V and U planes. Registered by Intel.