12 bit Video, hoe zit dat?

[rvvnr1]

Sinds kort heb ik hier een nieuwe televisie staan en nu viel mij op dat bij het gebruik van mijn Blu-Ray speler, ook zonder disc in de speler, de televisie aangeeft een 12 bit (en 1080p 24p) signaal te ontvangen.

Wat wil dit nu precies zeggen?
Snap niet helemaal hoe ik dit moet zien, had begrepen dat Blu-Ray tot 8 bit ging en er eigenlijk helemaal geen zogenaamde deepcolor schijven zijn uitgebracht.

En hoe moet ik die 8 en 12 bit zien in vergelijking met de tegenwoordig gebruikelijk 24 of zelfs 32 bit kleuren op een pc? Is toch wel een aardig verschil, of is dit niet met elkaar te vergelijken?

[DVDProfilersFilmgek]

Merk en model TV?

[rvvnr1]

Lijkt mij van geen enkel belang maar goed omdat jij t wil weten: een Sony Bravia KDL-32HX750

[DVDProfilersFilmgek]

Was nieuwsgierig naar het merk dat deze info geeft, dit terwijl het in mijn ogen wat minder nut heeft, maar goed de TV laat dan zien dat de speler een 12bit color signaal geeft. (vind het al prachtig dat mijn TV laat zien wat de resolutie en de frequentie van het signaal is )

Je vraagt nu zelf of het vergelijkbaar is, in weze wel, het gaat bij beiden immers om schermen en hoeveelheden data. Wel heel veel data, hier kunnen ze het beter vertellen dan ik het kan:

http://www.abccables.com/info-hdmi-deep-color-.html

Hoop dat je een beetje engels machtig bent.....

[Claudio Santulli]

Het is wat verwarrend maar, we hebben het feitelijk over verschillende eenheden.

De 12 en 16 bit slaan op "the number of bits per color."
De 36 en 48 bit slaan op "the total number of bits per pixel."

12 bits per color channel * 3 colors (red, green, and blue) = 36 bits per pixel.
16 bits per color channel * 3 colors (red, green, and blue) = 48 bits per pixel.

Het is dus eigenlijk hetzelfde maar onder een andere noemer.

Dan nog even dit. Het menselijk oog kan niet meer dan 8 bit kleur onderscheidden. En geeneen video weergever inclusief Blu/ray kan meer dan 8 bit kleur weergeven. En dat zal waarschijnlijk ook nooit gebeuren. We hebben het dus feitelijk over upscalen van bits.

[rvvnr1]

Bedankt voor beide reacties. Zal die link later nog eens doornemen.

Maar dat 36 en 48 bits zie ik bijvoorbeeld niet terugkomen op een pc, daar is het 24 bits wat ook wel true color werd genoemd en daarna volgde nog dat 32 bits. En ik zie net dat je nu tegenwoordig onder Windows 7 maar twee opties hebt: 16 bit (high color) en 32 bits (true color). Hou verhoudt dit, windows vs. ht, zich tot elkaar dan?

[Gerco Stuivenberg]

Bij Windows gaat het volgens mij vaak om het totaal wat de videokaart aan kan, terwijl het bij TV´s vaak alleen om de bron gaat. Het totaal wordt bij een TV nl. ook nog bepaald door de mogelijkheden van de processor van de TV.

Daarnaast zorgen de instellingen er voor dat een scherm niet alle kleuren kan laten zien die de processor kan generen en zal het werkelijke aantal kleuren dat het scherm zal weergeven bij een computer ongeveer net zo groot zijn als bij een TV, ongeveer 8 tot 10 bit.

[Hombre]

Het is wat verwarrend maar, we hebben het feitelijk over verschillende eenheden.

De 12 en 16 bit slaan op "the number of bits per color."
De 36 en 48 bit slaan op "the total number of bits per pixel."

12 bits per color channel * 3 colors (red, green, and blue) = 36 bits per pixel.
16 bits per color channel * 3 colors (red, green, and blue) = 48 bits per pixel.

Het is dus eigenlijk hetzelfde maar onder een andere noemer.

Dan nog even dit. Het menselijk oog kan niet meer dan 8 bit kleur onderscheidden. En geeneen video weergever inclusief Blu/ray kan meer dan 8 bit kleur weergeven. En dat zal waarschijnlijk ook nooit gebeuren. We hebben het dus feitelijk over upscalen van bits.

Ik denk dat hier een aantal zaken door elkaar worden gehaald.

Het aantal bits in de video heeft met de opslag te maken van het content. 12 bit 4:4:4 is uncompresed en neemt veel ruimte in...


8-bit 4:2:2 YUV = Blu-ray
10-bit 4:4:2 YUV = Cimema Digital Intermediate
12-bit 4:4:4 RGB = Cimema Digital Intermediate

Er zijn spelers en videopanelen die de 8 bits van de BD upscalen naar 10 of 12 bit...

[Claudio Santulli]

Wellicht, maar dat verandert niet veel aan mijn antwoord aan de vraagsteller.
Nog wat meer diepgaande info over dit.

Image Encoding Standards

The sections listed below provide important information about the image encoding standards supported by Color. The image data you’ll be color correcting is typically encoded either using an RGB or Y′CBCR (sometimes referred to as YUV) format. Color is extremely flexible and capable of working with image data of either type. For detailed information, see:

• The RGB Additive Color Model Explained
• The Y′CBCR Color Model Explained
• Chroma Subsampling Explained
• Bit Depth Explained

The RGB Additive Color Model Explained

In the RGB color model, three color channels are used to store red, green, and blue values in varying amounts to represent each available color that can be reproduced. Adjusting the relative balance of values in these color channels adjusts the color being represented. When all three values are equal, the result is a neutral tone, from black through gray to white.
More typically, you’ll see these ratios expressed as digital percentages in the Color Parade scope or Histogram. For example, if all three color channels are 0%, the pixel is black. If all three color channels are 50%, the pixel is a neutral gray. If all three color channels are 100% (the maximum value), the pixel is white.
Animation (an older, 8-bit codec) and Apple ProRes 4444 (a newer 10-bit codec) are the two most commonly used RGB QuickTime codecs. In digital intermediate workflows, RGB-encoded images are typically stored as uncompressed DPX or Cineon image sequences.

The Y′CBCR Color Model Explained

Video is typically recorded using the Y′CBCR color model. Y′CBCR color coding also employs three channels, or components. A shot’s image is divided into one luma component (luma is image luminance modified by gamma for broadcast) and two color difference components which encode the chroma (chrominance). Together, these three components make up the picture that you see when you play back your video.

• The Y′ component represents the black-and-white portion of an image’s tonal range. Because the eye has different sensitivities to the red, green, and blue portions of the spectrum, the image “lightness” that the Y′ component reproduces is derived from a weighted ratio of the (gamma-corrected) R, G, and B color channels. (Incidentally, the Y′ component is mostly green.) Viewed on its own, the Y′ component is the monochrome image.
• The two color difference components, CB and CR, are used to encode the color information in such a way as to fit three color channels of image data into two. A bit of math is used to take advantage of the fact that the Y′ component also stores green information for the image. The actual math used to derive each color component is CB = B′ - Y′, while CR = R′ - Y′.

Note: This scheme was originally created so that older black-and-white televisions would be compatible with the newer color television transmissions.

Chroma Subsampling Explained

In Y′CBCR encoded video, the color channels are typically sampled at a lower ratio than the luma channel. Because the human eye is more sensitive to differences in brightness than in color, this has been used as a way of reducing the video bandwidth (or data rate) requirements without perceptible loss to the image.
The sampling ratio between the Y′, CB, and CR channels is notated as a three-value ratio. There are four common chroma subsampling ratios:

• 4:4:4: 4:4:4 chroma subsampled media encodes completely uncompressed color, the highest quality possible, as the color difference channels are sampled at the same rate as the luma channel. 4:4:4 subsampled image data is typically obtained via telecine or datacine to an image sequence or video format capable of containing it, and is generally employed for digital intermediate and film workflows. RGB encoded images such as DPX and Cineon image sequences and TIFF files are always 4:4:4.
  The Apple ProRes 4444 codec lets you capture, transcode to, and master media at this high quality. (The fourth 4 refers to the ability of Apple ProRes 4444 to preserve an uncompressed alpha channel in addition to the three color channels; however, Color doesn’t support alpha channels.)
  Be aware that simply rendering at 4:4:4 doesn’t guarantee a high-quality result. If media is not acquired at 4:4:4, then rendering at 4:4:4 will preserve the high quality of corrections you make to the video, but it won’t add color information that wasn’t there to begin with.
  As of this writing, few digital acquisition formats are capable of recording 4:4:4 video, but those that do include HDCAM SR, as well as certain digital cinema cameras, including the RED, Thompson Viper FilmStream, and Genesis digital camera systems.
• 4:2:2: 4:2:2 is a chroma subsampling ratio typical for many high-quality standard and high definition video acquisition and mastering formats, including Beta SP (an analog format), Digital Betacam, Beta SX, IMX, DVCPRO 50, DVCPRO HD, HDCAM, and D-5 HD.
  Although storing half the color information of 4:4:4, 4:2:2 is standard for video mastering and broadcast. As their names imply, Apple Uncompressed 8-bit 4:2:2, Apple Uncompressed 10-bit 4:2:2, Apple ProRes 422, and Apple ProRes 422 (HQ) all use 4:2:2 chroma subsampling.
• 4:1:1 and 4:2:0: 4:1:1 is typical for consumer and prosumer video formats including DVCPRO 25 (NTSC and PAL), DV, and DVCam (NTSC).
  4:2:0 is another consumer-oriented subsampling rate, used by DV (PAL), DVCAM (PAL), and MPEG-2, as well as the high definition HDV and XDCAM HD formats.
  Due to their low cost, producers of all types have flocked to these formats for acquisition, despite the resulting limitations during post-production (discussed below). Regardless, whatever the acquisition format, it is inadvisable to master using either 4:1:1 or 4:2:0 video formats.

It’s important to be aware of the advantages of higher chroma subsampling ratios in the color correction process. Whenever you’re in a position to specify the transfer format with which a project will be finished, make sure you ask for the highest-quality format your system can handle. (For more information about high-quality finishing codecs, see A Tape-Based Workflow.)
As you can probably guess, more color information is better when doing color correction. For example, when you make large contrast adjustments to 4:1:1 or 4:2:0 subsampled video, video noise in the image can become exaggerated; this happens most often with underexposed footage. You’ll find that you can make the same or greater adjustments to 4:2:2 subsampled video, and the resulting image will have much less grain and noise. Greater contrast with less noise provides for a richer image overall. 4:4:4 allows the most latitude, or flexibility, for making contrast adjustments with a minimum of artifacts and noise.
Furthermore, it’s common to use chroma keying operations to isolate specific areas of the picture for correction. This is done using the HSB qualifiers in the Secondaries room. (For more information, see Choosing a Region to Correct Using the HSL Qualifiers.) These keying operations will have smoother and less noisy edges when you’re working with 4:2:2 or 4:4:4 subsampled video. The chroma compression used by 4:1:1 and 4:2:0 subsampled video results in macroblocks around the edges of the resulting matte when you isolate the chroma, which can cause a “choppy” or “blocky” result in the correction you’re trying to create.
Despite these limitations, it is very possible to color correct highly compressed video. By paying attention to image noise as you stretch the contrast of poorly exposed footage, you can focus your corrections on the areas of the picture where noise is minimized. When doing secondary color correction to make targeted corrections to specific parts of the image, you may find it a bit more time consuming to pull smooth secondary keys. However, with care and patience, you can still achieve beautiful results.
Film Versus Video and Chroma Subsampling

With a bit of care you can color correct nearly any compressed video or image sequence format with excellent results, and Color gives you the flexibility to use highly compressed source formats including DV, HDV, and DVCPRO HD.
Standard and high definition video, on the other hand, is usually recorded with lower chroma subsampling ratios (4:2:2 is typical even with higher-quality video formats, and 4:1:1 and 4:2:0 are common with prosumer formats) and higher compression ratios, depending entirely upon the recording and video capture formats used. Since the selected video format determines compression quality at the time of the shoot, there’s nothing you can do about the lost image data, other than to make the best of what you have.
In general, film footage is usually transferred with the maximum amount of image data possible, especially when transferred as a completely uncompressed image sequence (4:4:4) as part of a carefully managed digital intermediate workflow. This is one reason for the higher quality of the average film workflow.


Bit Depth Explained

Another factor that affects the quality of video images, and can have an effect on the quality of your image adjustments, is the bit depth of the source media you’re working with. With both RGB and Y′CBCR encoded media, the higher the bit depth, the more image data is available, and the smoother both the image and your corrections will be. The differences between images at different bit depths is most readily apparent in gradients such as skies, where lower bit depths show banding, and higher bit depths do not.
The bit depth of your source media depends largely on how that media was originally acquired. Most of the media you’ll receive falls into one of the following bit depths, all of which Color supports:

• 8-bit: Most standard and high definition consumer and professional digital video formats capture 8-bit image data, including DV and DVCPRO-25, DVCPRO 50, HDV, DVCPRO HD, HDCAM, and so on.
• 10-bit: Many video capture interfaces allow the uncompressed capture of analog and digital video at 10-bit resolution.
• 10-bit log: By storing data logarithmically, rather than linearly, a wider contrast ratio (such as that of film) can be represented by a 10-bit data space. 10-bit log files are often recorded from datacine scans using the Cineon and DPX image sequence formats.
• 12-bit: Some cameras, such as the RED ONE, capture digital images at 12-bit, providing for even smoother transitions in gradients.
• 16-bit: It has been said that it takes 16 bits of linear data to match the contrast ratio that can be stored in a 10-bit log file. Since linear data is easier for computers to process, this is another data space that’s available in some image formats.
• Floating Point: The highest level of image-processing quality available. Refers to the use of floating-point math to store and calculate fractional data. This means that values higher than 1 can be used to store data that would otherwise be rounded down using the integer-based 8-bit, 10-bit, 12-bit, and 16-bit depths. Floating Point is a processor-intensive bit depth to work with.

Higher bit depths accommodate more image data by using a greater range of numbers to represent the tonal range that’s available. This is apparent when looking at the numeric ranges used by the two bit depths most commonly associated with video.

• 8-bit images use a full range of 0–255 to store each color channel. (Y′CBCR video uses a narrower range of 16–235 to accommodate super-black and super-white.) 255 isn’t a lot of values, and the result can be subtly visible “stairstepping” in areas of the picture with narrow gradients (such as skies).
• 10-bit images, on the other hand, use a full range of 0 to 1023 to store each color channel. (Again, Y′CBCR video uses a narrower range of 64–940 to accommodate super-black and super-white.) The additional numeric range allows for smoother gradients and virtually eliminates bit depth–related artifacts.

Fortunately, while you can’t always control the bit depth of your source media, you can control the bit depth at which you work in Color independently. This means that even if the source media is at a lower bit depth, you can work at a higher bit depth to make sure that the quality of your corrections is as high as possible. In particular, many effects and secondary corrections look significantly better when Color is set to render at higher bit depths.

Bron

[rvvnr1]

Hartelijk dank voor de reacties!