cai-1: Raw data contains wrong number of images

Hi,

I am looking at the cai-1 dataset (the GCaMP5k_9cells_Akerboom2012 dataset) and I have a problem with the raw data, because there are twice as many images than calcium entries.

The tiff file of the first cell for example (cai-1/GCaMP5k_9cells_Akerboom2012/raw_data/20110714_cell1/cell1005.tif) contains 24.000 images, however, the frame rate is 50 Hz and the recording time 240 seconds, so there should only be 12.000 images. The extracted calcium that can be found in the processed data contains the correct number of 12.000 entries.

Can someone explain why there are too many images?

(I haven't checked all cells yet, but the GCaMP6k data set seem to contain the correct number of images.)

Thanks!

In a subset of experiments two fluorescence channels were recorded (green, relevant to GCaMP; red) and stored as interleaved images. Only alternating images are thus relevant to calcium imaging.

(Answer provided by Karel Svoboda).