Blue Only
With Blue Only mode is called a special mode for display devices ( projectors , displays, TV ), in which only the blue pixels or the blue cathode ray tube is used (old tube technology) to produce the image. In the broadcast sector in particular, display devices have this mode, as it allows the hue and saturation to be set quickly and precisely. For this purpose there is a separate button on professional monitors on the front of the display device.
Test images
In general, all test images with a color bar containing red, green, blue and the complementary colors cyan, magenta and yellow are suitable for the blue only mode and the adjustment of hue and saturation that can be carried out with it. However, the SMPTE test pattern or the HD variant of the SMPTE color bar is particularly often used for setting . In many cases, these are already integrated into the recording and playback devices in the professional sector and are available at any time. The Blue-Only test image from Burosch Audio Video Technik is also suitable for use with a blue filter film or in Blue Only mode. In addition to hue and saturation, the above-mentioned test images can also be used to set the brightness and contrast of the display devices. The Burosch test pattern mentioned is an update of the conventional HD-SMPTE test pattern, with additional test zones for complete image control and optimization.
functionality
In Blue Only mode, only the blue pixels - or, in the case of CRT monitors, the blue cathode ray tube - generate the image. Thus you can see the blue channel of the picture colored blue. Colored areas with blue color components appear light and those without blue color components appear dark. The color blue with the RGB values 0 0 255 thus appears light. A red area (255 0 0) or a green area (0 255 0), however, appears black. Below - or above in the case of some test images - the color bars are reference areas which, if adjusted correctly, must have the same brightness value as the associated color areas. If the display device is correctly adjusted, in the blue-only mode view, the colored areas fit into the reference areas without a difference in brightness. In the SMPTE-HD test image, the reference area is below the color bars in the form of a continuous gray area. With the old SMPTE test image, the reference area is also below the individual color bars. The Blue Only test image from Burosch has individual reference areas above and below the color bars for each color. The following table shows the individual colors, the associated code values and the visual impression in Blue Only Mode:
| colour | RGB values (8 bit) 75% brightness | Brightness impression in Blue Only Mode |
|---|---|---|
| red | 191 0 0 | Dark black) |
| green | 0 191 0 | Dark black) |
| blue | 0 0 191 | Bright |
| Cyan | 0 191 191 | Bright |
| magenta | 191 0 191 | Bright |
| yellow | 191 191 0 | Dark black) |
| 75% white | 191 191 191 | Bright |
| black | 0 0 0 | Dark black) |
| Reference area 75% white | 191 191 191 | Bright |
See figure on the right. Blue Only view of the ARIB / SMPTE test pattern.
Blue filter foils instead of blue only mode
As an alternative to the Blue Only mode, a blue filter foil can also be used in conjunction with the test images mentioned. If you look through this film, you can only see the blue parts of the test image. The degree of transmission is important when using such films . The films should have a very narrow-band transmission in the short-wave range of the visible spectrum and only let through the blue wavelengths of the light spectrum. If you still see other colors when looking through the foil, you can also use the foil twice. Another example of blue filter foils in connection with test images are the blue filter glasses from THX . Sometimes display devices are also adjusted with red or green filter foils. This allows the color rendering to be set correctly in all three channels.
Adjust saturation and hue
To do this, the display device must be switched to Blue Only Mode. If this is not possible, you can - as mentioned above - fall back on blue filter foils.
- First you set the saturation. To do this, change the value in the menu until the colored bars fade in seamlessly, with the same brightness and without any noticeable difference in the reference areas or below the color bars.
- When the colored bars no longer differ from the reference surfaces, the saturation is set correctly.
- The next step is to set the color correctly.
Often individual colored areas still stand out from the reference areas, or individual colored bars - which should actually be dark - still appear too light and stand out from the reference areas. This particularly often affects the cyan and magenta bars, but also includes the green color bar. In this case you have to adjust the color tone in the menu until these color bars also blend in perfectly and without any visible difference in the reference area. Further detailed instructions can be found in the web links.