Stefano Tommesani

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Comparing background subtraction algorithms

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The bgslibrary by Andrews Sobral includes over 30 background subtraction algorithms, a common C++ framework for comparing them, and an handy C++/MFC or Java app to see them running on video files or live feed from a webcam.

I have run all the background subtraction algorithms against a test sequence that is really hard, as the camera is slightly shaking and the trees are waving due to the strong wind, so building a reliable estimation of the background of this scene is definitely an hard task. The video sequence was also cropped so that it starts with moving objects already in the scene, to check how quickly the background subtraction algorithms react to permanent changes after the initialization. No filtering was performed on the results, as these videos are meant only to compare the relative performance of background subtraction algorithms.

BGSScreenShotEvery video highlighting an algorithm has the screen divided in quadrants:

  • the top-left quadrant shows the input video to be processed by the algorithm
  • the top-right quadrant shows the foreground mask (in white)
  • the bottom-left quadrant shows the estimated background; not every algorithm has an estimated background that can be displayed, so this quadrant may be blank
  • the bottom-right quadrant shows the name of the algortihm in the bgslibrary and the frame number
Last Updated on Wednesday, 18 September 2013 23:26

AskWatch: navigation

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After adding your kid, AskWatch will start grabbing data about your son for a few seconds, or a bit more depending on the speed of your internet connection. In the main window, a new tab with the name of your son will be added, and the new screen contains all the information about your son, in order:


Last Updated on Wednesday, 07 August 2013 22:59

AskWatch: adding your kids

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Start AskWatch from the Start screen (in Windows 8) or from the Start menu (in Windows 7). The following, mostly empty screen appears:


Last Updated on Wednesday, 07 August 2013 23:00

AskWatch: why you need it

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What is is a social Q&A site where users can ask other users questions. The questions can be from a named user, or completely anonymous. It is unmoderated (unless a user reports something), has no parental controls, and is an Latvian company. The concept seems harmless: you register, create a profile, and ask/answer questions that are posted to you. The problem is around the anonymity of the messaging. In the settings, you have the ability to block anonymous questions, but most users do not do this. You have the ability to blacklist users, assuming you know who they are. The terms of service says that you need to be 13 years old or older to join the site, but this is bypassed regularly.

Why should you worry for your kids?

Michael Sheehan said it best in his article named "Parents Be Warned! is a Dangerous & Deadly Social Site for Teens & Tweens":

Again, this seems relatively harmless, right? WRONG! is rapidly becoming a site for bullies and seemingly sex-crazed users (even if it is simply innuendos in messaging). And I believe that parents (especially in the US) don’t know much about yet. It seems that since this service originally launched in Europe, it had more attraction there initially. Since then it has come overseas to the States.
Last Updated on Friday, 09 August 2013 14:09

AskWatch: finding alarm words in conversations

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AskWatch can tag questions and answers that contain alarm words. For example, you may want to highlight messages related to sexual activities, such as the following one:


Last Updated on Wednesday, 14 August 2013 16:37

On bad web interfaces

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Today I have encountered the following error message in a major web site:



  • there was no warning on the web page about this limitation (e.g. "type up to 3000 chars")
  • there was no warning while typing that I was entering too much text, so that I would not waste time writing feedback that I cannot submit (no real-time hints)
  • I only knew about it at the end of the process, when I clicked on then Submit button at the bottom of the form and the request was rejected (slow feedback loop)
  • there was no information about how much the text I entered was longer that the maximum lenght allowed (e.g. "your text is 45 chars too long"), so I had no idea of how much should I shorten it (focus on the requirements, not on what the user is doing wrong). It became a slow trial-and-error experience, cutting a bit and clicking Submit, getting the error message and repeating again, and again... is this what you call "being user friendly"?

I see these UI mistakes daily. Many web sites, even from major brands, have terrible UIs that choke if entered data is only slightly different than what they expect, and signaling of errors happens only when users submit a whole form instead of providing local, real-time assistance with entered data not matching the specifications.

Last Updated on Saturday, 20 July 2013 00:46

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