Problems in displaying pictures in same size (mm) on different monitors


Problems in displaying pictures in same size (mm) on different...

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Lisa Eggert
Lisa Eggert
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Hey,


maybe one of you could help... I have the following problem: I try to define the size of pictures in mm, to ensure that every person sees the same one. This is necessary, because I want to do the experiment as a web experiment and therefore I want to have same "viewing conditions". Is there any possibility? Actually I even didn't succeed in displaying the pictures in the size in mm I entered. I already read in another post, that sometimes the display information is not read correct? What to do about this?


Thanks a lot for every hint!


Greetings from Germany :-)


Lisa


Dave
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Actually I even didn't succeed in displaying the pictures in the size in mm I entered. I already read in another post, that sometimes the display information is not read correct?


Computer displays work in terms of pixels. Pixels have no strict relation to any real, physical measurement unit (mm, cm, inch, etc.). I.e., what a pixel corresponds to in terms of mm, etc. depends on factors such as the physical dimensions of the display (visible, *not* nominal, diagonal), its set resulotion, its pixel density, dot pitch, etc. In other words: It will be different for every display. Except for screen resolution, none of these are known to any software.


The OS functions converting pixels to physical units are based on very general assumptions and results may vary considerably in accuracy due to the above.


What to do about this?


Nothing really, short of including some sort of calibration routine in your script (cf. the Spatial Delayed Response Task available from the Task Library). However, (1) you'd need Inquisit 3 to do that and (2) it would be pretty unsuitable for web use.


Regards,


~Dave


Lisa Eggert
Lisa Eggert
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So did I get you, it is not possible to show "physical identical" stimuli on different monitors? Even with web licence? Sorry for asking, I thought it would work... If there were a possibility to save certain values it would, but this is definetly not possible with version 2? The solution with values and expression I know, it worked with Version 3, but I do not have a web license 3... Thanks anyways!


Lisa


Dave
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So did I get you, it is not possible to show
"physical identical" stimuli on different monitors?


Correct. It's not possible. However, the OS functions at least give you a rough approximation. For the "real deal" you need to know the display's physical properties, i.e. you need to take at least a single measurement to establish the "true" pixel-to-mm correspondence for a given display and then size stimuli accordingly.


Even with web licence?


The issue is not specific to Inquisit, but solely due to how displays / digital images "work". It applies to any application.


If there were a possibility to save certain
values it would, but this is definetly not possible with version
2?


No, it can't be done w/ Inquisit 2.


~Dave


GO


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