Semi transparent stimuli and checkboard flash patterns

This forum deals with BCI2000 configuration issues.
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kpitt
Posts: 10
Joined: 06 Jun 2020, 22:30

Semi transparent stimuli and checkboard flash patterns

Post by kpitt » 06 Jun 2020, 22:38

Hi,

I am in the process of setting up the BCI2000 with P300 face speller paradigm, and had a couple of questions -

1) I was wanting to implement a semi transparent face flash paradigm that allows the grid letter/item to be seen behind the face when flashing. However, when I upload a semi-transparent image to BCI2000 it looks more like it has holes in it versus an overall semi transparency. Could anyone provide any direction about how to get the stimuli to look semi transparent?

Also, 2) is there a way to implement a checkboard flashing pattern in BCI 2000 instead of the traditional row/column?

Thank you for any help!

mellinger
Posts: 1163
Joined: 12 Feb 2003, 11:06

Re: Semi transparent stimuli and checkboard flash patterns

Post by mellinger » 08 Jun 2020, 10:55

Hi,
1) I was wanting to implement a semi transparent face flash paradigm that allows the grid letter/item to be seen behind the face when flashing. However, when I upload a semi-transparent image to BCI2000 it looks more like it has holes in it versus an overall semi transparency. Could anyone provide any direction about how to get the stimuli to look semi transparent?
By "semi transparent", do you mean the images have an alpha channel with the alpha value being different from 0 and 255? What BCI2000 does is that it looks whether an image has an alpha channel, and if yes, the alpha channel determines transparency. If the image has no alpha channel, the top left pixel's value is chosen to represent the transparent color. If your image has "holes", this sounds like the second case. You might have lost the alpha channel in some conversion process? You might have chosen a file format that does not support an alpha channel? PNG images should work fine with BCI2000.
Also, 2) is there a way to implement a checkboard flashing pattern in BCI 2000 instead of the traditional row/column?
It's not available to the end user, but changing the C++ source code to have stimuli flash in any groups you want is not difficult. If you know some programming and are prepared to compile BCI2000 from source, let me know.

HTH,
Jürgen

kpitt
Posts: 10
Joined: 06 Jun 2020, 22:30

Re: Semi transparent stimuli and checkboard flash patterns

Post by kpitt » 08 Jun 2020, 17:21

Thanks! i will look into this, and let you know if we want to pursue the checkboard. One step at a time :)

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