Chroma and luma keying

The previously discussed key operating modes were based on a chromatic keying. In most cases they will be sufficient for the user. But the Reckeen 3D Studio system also allows keying based on luminance.

When you select this mode and click on the first icon, you will see the following functions in the window.

• Box: Luma Color – clicking on the box allows you to select the keyed background color in the scope between white and black,
• Icon: Show Alpha Matte – a feature that allows you to enable or disable a view of a mask, where the represented image is shown in a gray scale, where:
  • black color is a completely transparent area,
  • white color is a completely opaque area.
• Slider: Cutoff – this is a function that allows widening the range of transparent colors by luminance similar to the luminance of the reference color (white or black).
• Slider: Softness – a function that, taking the luminance into account, enables widening the transition scope between the range of colors completely transparent and those fully opaque.

As before, you can save your settings to a *.recKey file to load them again in the future.

Also as before you have the functions Garbage Mask available.

In the luminance key mode, you can go to the tab: Post Correction and, just as before, introduce the changes in the view of the object (talent).

You can use a simplified version of the key settings by checking this mode in the window.

When you click on the button Simple Chrominance Keyer below the highlighted Mode button , a window with a simplified key settings opens up. The background color is selected with a probe. Clicking on the Pick color icon or on a color bar next to the icon, opens a window of a camera preview. Then, you have to select a location with a cursor and click there. The program will automatically sample the color as the background color and present it in the color box next to the probe icon.

The remaining number of sliders is limited to three: Black/White slider, Shadow slider, and Despill slider.

The Shadow slider is available only in the simple version of the key. There is a possibility of creating a shadow of the presenter, especially visible around the feet of the character, on the basis of incident light in the Green/Blue Screen studio. First you have to set the lighting so that , to get the shadow of the presenter on the green screen in the studio (on the floor in the studio). Then you can place this shadow on the floor in the virtual studio with Shadow slider . You can boost this shadow with the Shadow function.

Just as in the precise key mode, also in the simple mode you can turn on and off the mask by checking the Show Alpha Matte option.

The only thing left to do is to set the talent’s image post correction, just as with the precise key described earlier. All the other options are already automatically selected by the Reckeen 3D Studio system.

Also when you apply a simple key, you can save your settings to a *.recKey file using the Save function. Save icon is at the bottom right of the screen (as shown above).

You can access this function by clicking the Key Wizard icon at the bottom left side of the window.

The Key Wizard allows you to set the key with taking advantage of the instructions in the key wizard’s window. The Key Wizard will guide you through all the 6 steps of setting the key, suggesting which actions and when to perform.

To enable this function click on the Post Correction icon. This function allows you to adjust the object (a talent) to the lighting conditions of the virtual background. The post-correction, carried out with the sliders, will only concern the object (a talent) and so it will have no effect on the virtual background.

• Icon: Enabled – check this box to enable or disable the Post Correction.
• Slider: Brightness – this is a feature that allows you to bring additional brightness of the color into the talent’s image.
• Slider: Contrast – this feature allows you to increase contrast between colors.
• Slider: Saturation – this is a feature that allows you to increase color saturation.
• Color box: Ambient Color – this feature enables bringing the scene (ambient) color component into the talent’s image.
• Slider: Intensity – this is a feature that allows you to set the intensity of the ambient color.

The Post Correction functions are used to adjust the object (a talent – a figure of a presenter) to the background. This is possible by incorporating an additional component of a color already dominant in the virtual image. For example, when a background of a sunny beach is put under the discussed above object (talent) in the studio, you should add a yellow color (dominant color of sand and sun that affect the object) as Ambient Color. When you click on the Ambient Color icon, a color wheel window, where you select the exact color and hue, will open.

The color wheel shown in the picture above is based on RGB (Red, Green, Blue) model extended by Hue, Saturation, and Value.

The color can be set with the sliders available on the right side of the screen:

• Hue – the hue parameter corresponding to the colors on the edge of the color wheel – from 0 (red), through 120 (green) and 240 (blue) to 360 (red), – by changing the value of the slider, you change the position of
  the dash marker on the wheel.
• Saturation – the value of saturation parameter lays in a range of 0 (white) to 255 (100% full saturation), by moving the slider, you change the position of the black circle along one of the sides of the square.
• Value – the brightness parameter that lays in the in the range of 0 (black) to 255 (100% bright color of a given hue and saturation), by moving the slider, you change the position of the circle along one of the
  sides of the square.

You can also set all of these values with a cursor. You just need to hook the cursor on the dash marker. Changing the marker’s position on the wheel allows you to set the color by setting its Hue parameter. When you hook the cursor on the black circle, you can move this circle inside the square. This allows you to change all the remaining parameters. The current color will be visible in the middle of the black circle.

You can adjust the object to the conditions in the scene by setting the options of correction functions with the sliders. The figure of a talent will then gain a natural appearance.

After setting the key in this mode, you can save all of your settings to a file on your hard drive by clicking on the icon: Save in the lower right corner of the window.

The Reckeen 3D Studio system has its own key files – *.recKey . If the lighting conditions, hardware, etc. in the studio remain unchanged, then going back to the production screen, you can load your key’s settings from a file by clicking on the icon: Load.

This is a function used to cut off (reduce) the area of the mask (in all possible directions: left, right, up, down).

This function is used in the case where the view of the keyed background is not large enough to fill out the entire camera image.

A view of the camera’s image area.

You can set the object in the keyed background’s area by cutting off the remaining elements with Left/ Right and Top/Bottom sliders.

A view after the correction of the mask’s area with the keying algorithm off.

Once chroma key is enabled, you get the following effect.

Attention! Please note that, in this case, the object can move only within the area of the cut off mask – otherwise the object will disappear.

What’s more, if you use the mask’s area sliders, you can verify whether your previous settings were correct and whether they had any impact on the final appearance of the virtual background. By moving e.g. Left slider to its maximum, you should not encounter any noticeable noise, change in color or a in grayness of the background.

Edge Correction is an additional correction that improves the keying quality.

Click on the icon Edge Correction in order to open a window.

The Brightness function is responsible for correction of the semitransparent areas (like a correction of hair tips that should be darkened/brightened), affecting the image’s natural effect.

The Shrink function is responsible for reducing the object’s contour by softening it.

This is especially important for certain types of cameras, image from which can produce a white line around the object. It is possible to remove it with the Shrink function. You can also use it in the cases where keying is difficult in some places, due to the properties of the object’s edges or lighting. Be careful
not to trim the edges of the object too much, so that it doesn’t look unnatural.

Functions in the Spill Correction section eliminate from the object a reflection effect of the keyed background color. The picture below shows an impact of green color on the object – view before the spill correction.

Click on the icon Spill Correction to open the spill correction window. Despill Color and Despill Coarse functions are the functions used for preliminary elimination of unwanted color on the basis of RGB (red, green, blue) plane.

When you move the Despill Color slider to position 0 (to the left), the algorithm will automatically subtract the green color component, in the case when green is a keyed color (similarly blue when a blue background is used). Whereas moving it to a position 1000 (to the right) will cause adding color red with blue (when green is a keyed color) or red with green (in the case when a blue background was used) automatically by the algorithm.

You can control the value of the algorithm with Despill Coarse function. In the case of green background color, the Despill Coarse function entirely excludes a green component from the object in the RGB (red, green, blue) plane when it goes beyond a certain threshold, resulting in a shift of color to the purple
(magenta) area.

The next function enables more accurate improvement of the correction described above.

When you use the Despill Fine function, the color of the keyed background is excluded, but this time on the basis of chrominance components. Below you can see the Despill Fine slider.

After using the Despill Coarse function, which is an initial correction, the next step is to operate on the precise values. In the case where the Despill Coarse function was set at a high level, any changes in Despill Fine function settings may be of little significance to the algorithm.

As was shown in the previous picture, widening the scope with the White level function usually makes the plane, that formerly had a uniform black color, return to the light gray color scale.

In this case, to correct this gray, the two following functions from Tolerance Correction section are necessary.

Click on the button Tolerance Correction to open the tolerance settings window.

The first function – Luminance – improves the structure of the white mask’s uniform color.

The second function – Color – means returning to a single structure of the black background.

In particular, it improves visibility of an object, when there is a big difference in luminance between the object and the background. In this case, semitransparent objects, like a glass or eyeglasses, become more distinct.

Color function also fulfills a different task. It allows you to eliminate unnatural contours when you disable Show Alpha Matte and return to the actual image. You can remove these contours by improving the limit value between the keyed color and the object.

Click on the button Matte Control to set the initial keying parameters. It is done with the Show Alpha Matte function which, when enabled, shows a mask’s window in black and white. Parts of the mask’s image for which the colors are closer to white will be opaque, and those closer to the dark – transparent.

A view after clicking on the Show Alpha Matte icon.

The expected result is getting a black color of the mask’s background as perfect as possible. In order to achieve it, you have to move the markers on the Black/White slider up until you get as uniform distribution of the black color on the mask’s background as you can.

A view after the Black level correction

Moving the slider to the extreme positions will make the remaining objects lose their properties becoming opaque. Therefore, you have to carefully balance the extent to which you use this function, in order to reach a point where there are still some slight but noticeable differences in the distribution of the black background. The next step is to obtain a uniform distribution of white color on the objects that are to remain completely opaque. This non-uniformity may result from the fact that some of the object’s colors may have color components close to the keyed color. In this case, you can make adjustments using the White slider’s marker.

You can obtain a perfect distribution of a white color on the object by moving the slider towards the maximum value on the left.

A view after the White level correction.

In many cases, the option of White level setting is used together with the Black option, in order to obtain the most efficient settings possible of the black background – without losses in white objects and vice versa.

After selecting the operating mode of the key, the next step is to choose a background color. Click on the button Chrominance Keyer below the Mode button.

A window will appear, as shown below. Now you should choose a background color. There are two options: blue and green. You can change the background color by clicking on a rectangle with a green color. The color of the rectangle also changes then.

In the case of uneven color of the keyed background, you have a button: Detect Color at your disposal. It calculates LRGB parameters of the background on the basis of automated averaging. If reception of these parameters is not successful, the user is notified via a message window and then the default color is set. The Default Color button is used to select the default color.