SBC handscanning How-To

After you select the box “do handscan” and click “okay” in the pop-up, you’re ready to begin. The event viewer will automatically jump to the frame where any bubbles are initially tagged; ensure that “crosshairs” is selected so that you can see this initial tag or tags displayed in yellow. As you move through the frames by clicking “forward frame”, subsequent crosshairs will be drawn in red. To make the bubbles visible, you should also select one of the two “diff” options; “diff prev” will display the diff image between the frame denoted on the bottom left of the images and the previous frame, whereas “diff first” will display the diff image between that frame and the first frame (frame 0) of the event. Diffs between subsequent images allow for more stable lighting and a cleaner diff image, but diffs between a given frame and frame 0 may sometimes be better for making small bubbles more visible or larger bubbles appear more circular. Feel free to switch back and forth between these options as needed while handscanning. Another setting you can play around with to increase bubble visibility is “threshold”. Any pixels in the diff image with a value below this threshold will be set to zero. The default value of 10 is typically a good choice, but you can adjust this if you like.

Towards the end of an event, bubbles may reach the glass dome and deform or spread out against it. Thus, it may be difficult to tell the bubble multiplicity from just the final few frames. You should stop scanning forward using “forward frame” once the bubbles start to deform in this way. Take note of the maximal number of bubbles you’ve spotted in any one frame, even if some of those bubbles are not visible from another camera’s angle. The crosshairs can be helpful to guide your eye towards bubbles, but as the bubble finder is still being verified and improved, do not rely on them completely. You can turn them off as needed if they are obstructing your view. If a bright object is roughly circular or appears as a segment of a circle, increases in size throughout an event, and is consistently visible, you can be confident that it is a bubble. Note that bubbles on the walls of the jar may appear semicircular or as rounded boomerang shapes even before they have reached the dome at the top of the jar. Where two or more bubbles are very close together or even touching, look out for lines separating boomerang shapes to distinguish the bubbles and get an accurate count.

Once you have determined the maximal number of visible bubbles, select the corresponding bubble multiplicity (0-7+). If you did not see any bubbles, de-select “Is good trigger?”; keep it selected otherwise, since we want to verify that we are actually triggering on events where there is visual evidence that a bubble has nucleated. There is a bit more flexibility for “Crosshairs good?” since the bubble finder is still being improved. If the bubble was consistently tagged in the correct location in a single-bubble event, or if at least two bubbles were consistently tagged in one or more cameras in a multi-bubble event, leave it selected. It is not strictly necessary, but greatly appreciated if you leave a comment for events where bubbles are consistently double-tagged or where at least two but not all bubbles are tagged in a multi-bubble event. It is also helpful to leave a comment if you see the bubble(s) clearly appearing more than two frames before the t0 frame.

Finally, determine the location of the bubble(s). For this, it may help to select “no diff” so that the sides and top of the jar are fully visible. If a bubble appears to be completely separated from the glass surface at the t0 frame or when it is small, select “bulk event”; these bubbles are also typically nice and circular. You should select “wall” when the bubble has nucleated on the glass surface, whether that be on the side wall or on the top of the inner jar (bottom of the active region). In such cases, confirm by looking for a tail behind the bubble as you scan through the frames, as this is evidence of continued vapor production at the surface. Select “dome” if the bubble is already large and located at the top of the jar from the first frame of the event, as this is consistent with a gas pocket at the top of the chamber. Finally, choose “bellows region” if the bubble appears to rise out of the dark, annular region between the jars, located at the bottom of the chamber.

Once you have completed these steps, click “Submit and Go” to save your selections in a text file. These handscanning files will be saved in /exp/e961/data/SBC-25-handscan. Please also keep track of your handscanning in the spreadsheet under the “Handscan Campaign” tab. Happy handscanning!