Pixel Meter Node

The Pixel Meter node enables you to sample color values in selected areas of an image sequence. This data can then be displayed in the Pixel Meters window, or it can be accessed by other nodes.

The Pixel Meter node accepts one input. The Pixel Meter node must be connected to an Exec node to actuate the pixel metering process. Chalice will store the resulting data in the Pixel Meter node.

Tip:
If the Exec node contains more than one sequence entry, turn off all other entries before executing the metering sequence to avoid unnecessary processing. For more information, see the Exec Node description.

Meters Parameter Tab

The Meters parameter tab enables you to specify the size and location of an area (or "pixel meter") in an image. The pixel metering function, which is actuated by the Exec node, will then calculate an average of the RGBA values present in the area of the image you specified.

Work Monitor

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At Resolution

First, select a display resolution for the work monitor from the At Resolution popup menu. Then click the plus icon to display the work monitor for this node, which enables you to interactively position pixel meters in the image. For each pixel meter you create by clicking the Add Pixel Meter bar, a corresponding pixel meter appears in this monitor.

See Pixel Values

The plus button displays the Pixel Meters panel, which lists the average of the values contained in each of the RGBA channels for each pixel meter for the current frame. Values can be displayed as integer or floating point data, by pressing the Integer or Float buttons at the bottom of the Pixel Meters panel.

You can use the Frame Controller to change the current frame, and the values displayed in the Pixel Meters window will update accordingly.

Add Pixel Meter

Each time you click the Add Pixel Meter button, Chalice adds an additional pixel meter in the lower-left corner of the image in the Meter Monitor and makes an additional entry in the Pixel Meter List.

Pixel Meter Entries

A corresponding entry panel is created in the Meters tab for each pixel meter that you create. For each entry you can specify the position of the pixel meter and the size of the area to be sampled.

X Position and Y Position

You specify the location of each pixel meter by keying a numerical value into the X Position and Y Position data entry fields. Alternatively, you can use the work monitor to interactively position pixel meters. The data entry fields will update accordingly.

X Size and Y Size

You specify the size of each pixel meter (the dimensions of the area being sampled) by keying a numerical value into the X Size and Y Size data entry fields or by using the mouse to set the tuners to the desired values.

Delete Button

Click the red "X" button to delete an entry from the Pixel Meters list.

STED Button

Each Pixel Meters list entry includes a STED button, which you can click to display the Chalice Space-Time Editor. You can use the STED to view the pixel meter values computed thus far as a graph. The STED will also enable you to animate the pixel meter location and size over a range of frames. For more information, see chapter 9, "Space-Time Editor (STED) ."

Using Pixel Meter Data in Conjunction with Other Nodes

You can use pixel meter data to make color adjustments in other nodes, such as Brightness, by entering into the parameter field of the other node an expression that uses the following syntax:

meters("meters node name", , , )

The Red channel is 0, Green is 1, Blue is 2, and the Alpha channel is 3.

For example, keying the expression meters("meters1", 1, 0, $F) into the Brightness parameter (Expressions must be checked to key in the expression) would reference the red channel data for the current frame from pixel meter number 1 of a Pixel Meter node named "meters1." (For more information, see appendix B, "Chalice Expression Language .")

Using Other Node Data in Conjunction with the Pixel Meter Node

You can also use data from other nodes in conjunction with the Pixel Meter node. For example, you can access tracking data that you have already generated in a Track node to drive the position of a pixel meter to obtain average RGBA values for a moving object.

Follow these steps:

  1. Connect the node containing the image for which you wish to obtain pixel meter data to a Meters node, and connect the Meters node to the Exec node.
  2. In the Meters node panel, click the Add Pixel Meter bar.

  3. A corresponding pixel meter entry will appear in the Pixel Meters list.
  4. Check the Expressions box and enter the following expressions into the X and Y Position fields of the pixel meter entry:
  5. track("track1",XV,1,$F)

    track("track1",YV,1,$F)

    Note:
    Replace the name "track1" in these expressions with the name of the particular Track node that contains the tracking data you wish to reference. (Be sure to retain the quotation marks around the node name.)
  6. In the Exec node panel, press the Execute button.

  7. Chalice will calculate the values and store them in the Meters node.
  8. In the Pixel Meter node panel, press the See Pixel Values button.

  9. Chalice will display the Pixel Meters panel, which lists the RGBA values for each pixel meter at the current frame.
  10. Open the Pixel Meter work monitor to display the current position of each pixel meter in the image.




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