Attention PB Owners: Your screen is incapable of displaying millions of colors. Sorry

Comments

• Reply 1 of 2

  mmmpie Posts: 628member

  September 26, 2003 2:54AM

  Shame this thread is at MacNN where Im not going to post.
  
  
  
  It comes down to this:
  
  
  
  The crystals in an LCD respond to a change in voltage by twisting ( more or less ). The voltage is proportional to the value of the colour you want the LCD to display.
  
  
  
  When the colour changes a little bit, the voltage to that pixel/crystal changes a little bit.
  
  
  
  Unfortunately, the crystals respond slower to smaller voltage changes ( a lot slower ), ie: a change from black to white corresponds to a high voltage change, and a fast response, while grey to grey is a much smaller change and takes much longer.
  
  
  
  The result of all this is that when you watch movies, games, scrolling photos etc the changes in colour from frame to frame a quite small, and the pixels cant keep up. This causes the ghosting that people often complain about.
  
  
  
  In response to these complaints a lot of display manufacturers have released high speed 16ms screens. How do they do it you ask? The reduced the colour depth of the display. By making the display 6 bit the colour change for each pixel is much larger, and faster than for 8 bit.
  
  
  
  Screens rated for 25ms response times display 8 bit depth.
  
  
  
  Mitsubishi have developed an technique that drives pixel changes at full voltage for a short period, making colour changes much faster ( no faster for black to white ). However, none of the manufacturers indicate whether they use this technique. It is quite possible that they do, and that it is only capable of resolving 6 bit colour in these first generation products.
  
  
  
  It is unfortunate that Apple are using 6 bit displays in their powerbooks. Does it affect all of the displays? Or only the new 17"?
  
  
  
  For the average user ( 17" iMac ) its not a big deal, users getting 17" powerbooks probably expect better.
  
  
  
  In the end, professionals still use CRT's, LCD's just arent up to snuff, even Apple's.
• Reply 2 of 2

  skipjack Posts: 263member

  September 26, 2003 3:34AM

  Quote:
  

  
  Originally posted by trublue
  
  http://forums.macnn.com/showthread.p...32#post1604732
  
  
  
  Lets please discuss this here at AppleInsider.
  
  
  

  
  

  
  
  Since the claim is that PowerBooks since the G3 (Bronze series) have been able to support millions of colors, there must be an explanation that this issue has not been brought up before.
  
  
  
  Apparently, screens that have individual pixels which can display 256 colors are still able to display colors from the entire 16.7 million color range by combining clusters of pixels to form a color.
  
  
  
  From www.pctechguide.com
  
  
  
  "The 256-colour mode uses a level of indirection by introducing the concept of a "palette" of colours, selectable from the entire range of 16.7 million colours. Each colour in the 256-colour palette is defined using the standard 3-byte colour definition used in true colour: 256 possible intensities for each of red, blue and green. Any given image can then use any colour from its associated palette.
  
  
  
  The palette approach is an excellent compromise solution allowing for far greater precision in an image than would be possible by using the 8 bits available by, for example, assigning each pixel a 2-bit value for blue and 3-bit values each for green and red. Because of its relatively low demands on video memory the 256-colour mode is a widely used standard, especially in PCs used primarily for business applications."
  
  
  
  From Apple's Technical documents
  
  
  
  Dithering
  
  A technique for alternating the values of adjacent dots or pixels to create the effect of intermediate values. In printing color or displaying color on a computer screen, the technique of making adjacent dots or pixels different colors to give the illusion of a third color. For example, a printed field of alternating cyan and yellow dots appears to be green. Dithering can give the effect of shades of gray on a black-and-white display, or more colors on a color display.
  
  
  
  From Silicon Graphics technical documents:
  
  
  
  Dithering
  
  The simulation of more colors and shades in a palette by creating a pattern of dots out of existing colors. In an LCD that does not have true 24-bit color, frequently additional colors are simulated by this method. Dithering cannot produce the same results that a higher color depth (levels of gray or colors) allows, although it can make shaded drawings or images appear more realistic than they otherwise would.
  
  
  
  Dithering
  
  Dithering substitutes combinations of colours that a graphics card is able to generate for colours that it cannot produce. For example, if a graphics subsystem is capable of handling 256 colours, and an image that uses 65,000 colours is displayed, colours that are not available will be substituted by colours created from combinations of colours that are available. The colour quality of a dithered image is inferior to a non-dithered image.
  
  
  
  Dithering also refers to a technique that uses two colours to create the appearance of a third, giving a smoother appearance to otherwise abrupt transitions. In other words, it is also a method of using patterns to simulate gradations of grey or colour shades, or of anti-aliasing.
  
  
  
  There has been a lawsuit which involved dithering, which was used by Palm in the m130. The issue was Palm claimed that the screen could display over 64K colors. However, the dithering technique used only produced less than 59K colors. In other words, with regard to this thread, dithering has been an accepted technique for extending 256-color or "high color" displays to simulate "true color" displays for many years. This thread would be valid if Apple's dithering technique were not capable of displaying as many as 2 million colors ("millions"). Perhaps there is an expert who could tell us how many colors can be produced, using dithering, from the 6-bit per RBG channel screen.
  
  
  
  Second edit: from tomshardware.com
  
  "A major problem with LCD panels found in most notebooks is that they are limited to an 18-bit color depth (6 bits per color component). Although it is possible to change the color setting in the control panel to 32-bit color, it really makes no difference in visual quality. ATI addresses this issue in the Mobility Radeon 7500 with its new Frame Modulation technology, which brings the 18-bit LCD panels up to 24-bit, improving the overall quality of the display. Frame modulation creates intermediate color levels, which lead to an 8-bit-per-color component that uses temporal and special dithering."
  
  
  
  So, it looks like dithering allows the display of 16.7 million colors from a 6-bit per channel monitor.