Analyzing the Intensity of a Frame Sequence

You can analyze your footage to find out the average intensity values in it:

Select Image > CurveTool to add a CurveTool node in an appropriate place after the image sequence you want to analyze and match.

Connect a Viewer to the CurveTool.

In the node’s controls, select Avg Intensities from the Curve Type dropdown menu.

Select the channels you want to analyze from the channels dropdown menu and checkboxes.

By default, the region of interest that is to be analyzed covers the entire frame. If you want to analyze a smaller area, resize and reposition the region of interest in the Viewer by dragging its edges to a new position. You can also resize the region of interest using the ROI parameters in the properties panel.

In the # frames for base average field, enter the range of frames that each frame being analyzed is compared against. The frames are compared onwards from each frame analyzed. Thus, a value of 1 would compare each frame to the frame following it, whereas a value of 5 would compare each frame to the following 5 frames.

The higher frame range you use, the more accurate and time-consuming the calculation becomes. However, a high frame range is not always needed. For analyzing and matching fire flicker, you’d probably want to go frame by frame, whereas removing flicker would require a wider frame range to ensure a good average is obtained as the result.

To analyze the sequence, click Go!. This opens the Frames to execute dialog.

In the dialog, specify the frame range you want to analyze and match. Enter the first frame, followed by a comma and the last frame. Click OK. Nuke now analyzes the frame sequence.

Move to the IntensityData tab where you’ll find the results of the analysis. You’ll notice that the parameter input fields have turned blue. This indicates that they are animated. To see the animation curve, right-click on the values and select Curve editor.

Once Nuke has created the animation curve, you can copy the animation or any of its values into a color correction node, for example, to match the analyzed intensity there. Ctrl/Cmd+click on the animation button and drag and drop it to another parameter to create an expression linking the two.