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• How do people prove the correctness of Computer Vision methods?

  - by solvingPuzzles

  I'd like to pose a few abstract questions about computer vision research. I haven't quite been able to answer these questions by searching the web and reading papers. How does someone know whether a computer vision algorithm is correct? How do we define "correct" in the context of computer vision? Do formal proofs play a role in understanding the correctness of computer vision algorithms? A bit of background: I'm about to start my PhD in Computer Science. I enjoy designing fast parallel algorithms and proving the correctness of these algorithms. I've also used OpenCV from some class projects, though I don't have much formal training in computer vision. I've been approached by a potential thesis advisor who works on designing faster and more scalable algorithms for computer vision (e.g. fast image segmentation). I'm trying to understand the common practices in solving computer vision problems.

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• Easy Flood Fill

  - by Jimmy

  Some advice, please. I'm just starting out in C#. I've managed to get some shapes created on a Windows form, and now I'd like to fill them with color. In the old C++ I studied years ago, there was a floodfill function that was really easy. It has been an unpleasant realization to find there's not a similar method available in regular old C#. Does anyone have advice for me, or some code, so I can implement filling without understanding GDI+, DirectX, or rest of the avalanche of acronyms that I've run into by researching this on the web? I need to fill irregular shapes, bounded by a certain color. Gradient and transparency control would be nice, but I'd settle for plain old solid fill right now, just to get a modicom of control over this. Any help, code or advice would be really appreciated.

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• Variable 'app' in url-pattern for servlet mapping

  - by Brian

  I'm learning Spring MVC (and servlets in general) and following springsource's mvc-ajax example, which uses annotated controller methods. It appears that there is only one url-pattern (in web.xml) mapped to a servlet in that example: /app/* I've deployed the app as a WAR file, and the actual, ugly URL I'm requesting is http://127.0.0.1:8080/org.springframework.samples.mvc.ajax-1.0.0-20100407.233245-1/account. So, it appears that 'app' in '/app/*' is a variable corresponding to 'org.springframework.samples.mvc.ajax-1.0.0-20100407.233245-1', however, it isn't universal because it isn't usable in my own app, and it contradicts my understanding that url-pattern contains the portion of the URL after the app name. So, what is 'app'? Where is it configured?

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• Why does this window object not have the eval function?

  - by Motti

  I ran into an interesting (?) problem in the YUI rich edit demo on IE. When looking at the window object for the content editable frame used as the browser I see that the eval function is undefined (by running the following). javascript:alert(document.getElementById("editor_editor").contentWindow.eval) This only happens on IE (I checked on IE6 and IE8), and it doesn't happen on Firefox or Chrome. All the other window functions and properties seem to be in order, now I realise that eval is not really defined on the window but on the global object but my understanding was that in browsers the window is the global object (also eval does appear on all other windows so why not on this one?). Does anyone know if this is a know bug/limitation in IE and how I can get to eval in the context of the global object of this frame? (I need the side effects to be available to anything running from within this frame).

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• GWT's JSONParser producing incorrect values for numbers.

  - by WesleyJohnson

  I'm work with GWT and parsing a JSON result from an ASP.NET webservice method that returns a DataTable. I can parse the result into a JSONvalue/JSONObject just fine. The issue I'm having is that one my columns in a DECIMAL(20, 0) and the values that are getting parsed into JSON aren't exact. To demonstrate w/o the need for a WS call, in GWT I threw this together: String jsonString = "{value:4768428229311981600}"; JSONObject jsonObject = JSONParser.parse( jsonString ).isObject(); Window.alert( jsonObject.toString() ); This in turn alerts: {"value":4768428229311982000} I'm under the understanding that GWT's JSONParser is just using eval() to do the parsing, so is this some sort of number/precision issue with JavaScript that I've never been aware of. I'll admit I don't work with numbers that much in JavaScript and I might be able to work around this by changing the .NET WebService to return this column as string, but I'd really rather not do that. Thanks for any help.

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• Why can .NET not have memory leaks?

  - by Dinah

  Ignoring unsafe code, .NET cannot have memory leaks. I've read this endlessly from many experts and I believe it. However, I do not understand why this is so. It is my understanding that the framework itself is written in C++ and C++ is susceptible to memory leaks. Is the underlying framework so well-written, that it absolutely does not have any possibility of internal memory leaks? Is there something within the framework's code that self-manages and even cures its own would-be memory leaks? Is the answer something else that I haven't considered?

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• How safe am I signing into Google Spreadsheets with yeroon.net/ggplot2

  - by Farrel

  I am impressed by what I have seen of yeroon.net/ggplot2 which is a web interface for Hadley Wickham's R package ggplot2. I want to try it out on my own data. The part that has me very excited is that one can use data stored in one's own Google spreadsheet as the data. One just signs into their Google Account so that yeroon.net/ggplot2 can access the spreadsheet list. I have been hesitant to do it. If I sign in whilst on yeroon.net am I handing over my username and password to a third party? It would not be wise of me to divulge my google password to third parties since Google is fast becoming my repository of everything. How do I know if Jeroon's application is using ClientLogin or OAuth? My understanding is very basic and may be wrong but nevertheless here it is. OAuth would be better since it does not actually pass the password onto the third party application.

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• Nothing = String.Empty (Why are these equal?)

  - by Ek0nomik

  I find it very puzzling that null equals String.Empty in VB.NET. There must be an explanation for it that I'm not understanding. Somehow, when the equality of String.Empty (which has an object type of string) is tested against Nothing (which has no type) the test returns true. It just seems like a turn around in logic to me. In SQL if I were to compare an empty char or varchar against a null value, the test wouldn't return true. A null value is not the same as an empty string in this case. Yet in VB.NET they are equal. I'd love it if someone could provide a good explanation around this.

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• Code Signing Services

  - by bogdan

  I'm developing a System Preference Pane that runs a background application. I'm planning on codesigning the background application and I'll be using the kill flag of codesign (http://gemma.apple.com/mac/library/documentation/Darwin/Reference/ManPages/man1/codesign.1.html). From my understanding, this kill flag will not allow the background application to be run if it's signature doesn't match. My problem with this approach is that it doesn't provide any feedback to the user and, for somewhat reason, the application gets corrupted, it will refuse to launch without any information. I'd like to use the Code Signing Service from the System Preference Pane to check the validity of the background application. However, I couldn't find how to use it to check the validity of an external file. Is this possible using the Code Signing Service or should I NSTask codesign directly? My application is targeted for 10.6 so it doesn't matter which I use. Thank you!

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• Compiling a C program with a specific architecture

  - by Marplesoft

  I was recently fighting some problems trying to compile an open source library on my Mac that depended on another library and got some errors about incompatible library architectures. Can somebody explain the concept behind compiling a C program for a specific architecture? I have seen the -arch compiler flag before and have seen values passed to it such as ppc, i386 and x86_64 which I assume maps to the CPU "language", but my understanding stops there. If one program uses a particular architecture, do all libraries that it loads need to be on the same architecture as well? How can I tell what architecture a given program/process is running under?

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• C# -Closure -Clarification

  - by nettguy

  I am learning C#.Can I mean closure as a construct that can adopt the changes in the environment in which it is defined. Example : List<Person> gurus = new List<Person>() { new Person{id=1,Name="Jon Skeet"}, new Person{id=2,Name="Marc Gravell"}, new Person{id=3,Name="Lasse"} }; void FindPersonByID(int id) { gurus.FindAll(delegate(Person x) { return x.id == id; }); } The variable id is declared in the scope of FindPersonByID() but t we still can access the local variable id inside the anonymous function (i.e) delegate(Person x) { return x.id == id; } (1) Is my understanding of closure is correct ? (2) What are the aditional advantages can we get from closures?

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• How to play Sound and Animations in MVVM

  - by user275561

  I have read alot of blogs about the best way to play sound/Animation but if possible I would like to see a simplified example on how this is done so I understand better. So to my understanding in MVVM The View--Sound and Animation The ViewModel--If some value is true, i would like to play the Sound and Animation on the view. Now How would I go about doing this. I was told to use interfaces like ISoundService and IAnimationService. Implement in the View and then do what? If possible, a workable bare bone example will help alot.

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• Difference between "traditional" COM and COM+ (in Component Services)

  - by kizzx2

  By the "traditional" way I mean registering the DLL in registry. There seems to be another method to set up it by going to mmc-Component Services-COM+ Applications and adding the .tlb file. I have a COM library that supports both methods. When it installs, it registers itself in the registry as a COM component and it works fine. However, when I added the .tlb file using the Component Services method, the behavior seems to be different and it starts giving out errors. I suspect it has something to do with marshaling and inter-process object transfer? (Sorry, I'm really a noob in the COM area) Can anyone point me to a good resource to clear my understanding?

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• Parsing JPEG file format: Format of entropy-coded segment (ECS) segments?

  - by me2

  I'm having difficulty understanding the ITU-T T.81 spec for the JPEG file format. Hopefully someone else here has tried to parse JPEG files and/or knows about the details of this file format. The spec indiates that the ECS0 segment starts after the SOS segment but I can't find where in the spec it actually talks about the format of the ECS0 segment or how do detect its start. Simple JPEG implementations online are of limited help because they assume many things about the JPEGs they parse. Can anyone point me in the right direction?

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• TIBRV: Remote vs Local RVD

  - by jsw

  When connected to a local RVD a sending application is shielded from network interruptions and the send message methods will only block for the time it takes for the message to reach the local RVD process. With remote RVD the sending application is no longer shielded from network interruptions and the send message methods will block for the time it takes to hop across the network to reach the remote RVD process. Is my understanding correct? The documentation is vague regarding remote daemons. I'm mostly concerned with how reliable and performant the send message will be from the perspective of a sending application. Introducing unnecessary blocking on the client side due to sending a message (especially a network hop) is a big no-no in this application. The speed at which the messages reach the consumer is not of the utmost importance. With this in mind is a remote RVD out of the question?

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• Dereferencing pointers without pointing them at a variable

  - by Miguel

  I'm having trouble understanding how some pointers work. I always thought that when you created a pointer variable (p), you couldn't deference and assign (*p = value) unless you either malloc'd space for it (p = malloc(x)), or set it to the address of another variable (p = &a) However in this code, the first assignment works consistently, while the last one causes a segfault: typedef struct { int value; } test_struct; int main(void) { //This works int* colin; *colin = 5; //This never works test_struct* carter; carter->value = 5; } Why does the first one work when colin isn't pointing at any spare memory? And why does the 2nd never work? I'm writing this in C, but people with C++ knowledge should be able to answer this as well.

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• Why Bluetooth needs DBUS way of communication in android?

  - by Rajesh SO

  I am newbie to Android DBUS, recently I was informed that I need to use DBUS to implement Bluetooth in Android, from DBUS documentation I see DBUS is used for communication medium between two applications. In Android apps -apps communication is through intents, if so why do we need DBUS for Bluetooth ? Is that DBUS serves as communication medium for networking (IP) between two apps since it is built over sockets? Please correct me if my understanding is wrong, any more information on DBUS along with Bluetooth implementation in Android is appreciated. Thanks.

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• copying a jar file in Apache Ant

  - by synchronicity

  I need to copy a jar file from one directory to another when my project is built. Placing the statement: <copy file="${test.dir}/MyFirstTest.jar" todir="${share.path}"/> works fine when the project is built alone, but if I clean and build the project I get a warning informing me that the ${test.dir}/ directory hasn't been created yet. If I'm understanding properly I should be able to create a 'target' and specify a dependency for this operation but I'm unsure of what dependency to specify. What series of statements do I need to use to ensure this copy will occur whether I clean and build or just build the project? Please let me know if any further clarification is needed. FYI I am using Netbeans 6.8 to build my project.

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• Windows code pages, what are they?

  - by Mike D

  I'm trying to gain a basic understanding of what is meant by a Windows code page. I kind of get the feeling it's a translation between a given 8 bit value and some 'abstraction' for a given character graphic. I made the following experiment. I created a "" character literal with two versions of the letter u with an umlaut. One created using the ALT 129 (uses code page 437) value and one using the ALT 0252 (uses code page 1252) value. When I examined the literal both characters had the value 252. Is 252 the universal 8 bit abstraction for u with an umlaut? Is it the Unicode value? Aside from keyboard input are there any library routines or system calls that use code pages? For example is there a function to translate a string using a given code table (as above for the ALT 129 value)?

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• Accessing structure elements using pointers

  - by Arun Nadesh

  Hi Everybody, Greetings! I got surprised when the following program did not crash. typedef struct _x{ int a; char b; int c; }x; main() { x *ptr=0; char *d=&ptr->b; } As per my understanding the -> operator has higher precedence over & operator. So I expected the program to crash at the below statement when we try to dereference the NULL pointer tr. char *d=&ptr->b; But the statement &ptr->b evaluates to a valid address. Could somebody please explain where I'm wrong? Thanks & Regards, Arun

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• ado.net managing connections

  - by madlan

  Hi, I'm populating a listview with a list of databases on a selected SQL instance, then retrieving a value from each database (It's internal product version, column doesn't always exist) I'm calling the below function to populate the second column of the listview: item.SubItems.Add(DBVersionCheck(serverName, database.Name)) Function DBVersionCheck(ByVal SelectedInstance As String, ByVal SelectedDatabase As String) Dim m_Connection As New SqlConnection("Server=" + SelectedInstance + ";User Id=sa;Password=password;Database=" + SelectedDatabase) Dim db_command As New SqlCommand("select Setting from SystemSettings where [Setting] = 'version'", m_Connection) Try m_Connection.Open() Return db_command.ExecuteScalar().trim m_Connection.Dispose() Catch ex As Exception 'MessageBox.Show(ex.Message) Return "NA" Finally m_Connection.Dispose() End Try End Function This works fine except it's creating a connection to each database and leaving it open. My understanding is the close()\dispose() releases only the connection from the pool in ado rather than the actual connection to sql. How would I close the actual connections after I've retrieved the value? Leaving these open will create hundreds of connections to databases that will probably not be used for that session.

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• Using comet with PHP?

  - by ryeguy

  I was thinking of implementing real time chat using a PHP backend, but I ran across this comment on a site discussing comet: My understanding is that PHP is a terrible language for Comet, because Comet requires you to keep a persistent connection open to each browser client. Using mod_php this means tying up an Apache child full-time for each client which doesn’t scale at all. The people I know doing Comet stuff are mostly using Twisted Python which is designed to handle hundreds or thousands of simultaneous connections. Is this true? Or is it something that can be configured around?

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• What to pass to UserType, BlobType.setPreparedStatement session parameter

  - by dlots

  http://blog.xebia.com/2009/11/09/understanding-and-writing-hibernate-user-types/ I am attempting to defined a customer serialization UserType that mimics, the XStreamUserType referenced and provided here: http://code.google.com/p/aphillips/source/browse/commons-hibernate-usertype/trunk/src/main/java/com/qrmedia/commons/persistence/hibernate/usertype/XStreamableUserType.java My serializer outputs a bytearray that should presumably written to a Blob. I was going to do: public class CustomSerUserType extends DirtyCheckableUserType { protected SerA ser=F.g(SerA.class); public Class<Object> returnedClass() { return Object.class; } public int[] sqlTypes() { return new int[] {Types.BLOB}; } public Object nullSafeGet(ResultSet resultSet,String[] names,Object owner) throws HibernateException,SQLException { if() } public void nullSafeSet(PreparedStatement preparedStatement,Object value,int index) throws HibernateException,SQLException { BlobType.nullSafeSet(preparedStatement,ser.ser(value),index); } } Unfortunetly, the BlobType.nullSafeSet method requires the session. So how does one define a UserType that gets access to a servlet requests session? EDIT: There is a discussion of the issue here and it doesn't appear there is a solution: Best way to implement a Hibernate UserType after deprecations?

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• A question about some code from TBB book, Thanks.

  - by Jackie

  I am reading the book: Intel Threading Building Blocks. I often have difficulties understanding them. For example,the following code is from the book(page 112): Node* AllocateNode() { Node* n; FreeListMutexType::scoped_lock lock; lock.acquire(FreeListMutex); n=FreeList; if(n) Freelist=n->next; lock.release(); if(!n) n=new Node(); return n; } There is other introduction regarding this code. I can not understand it. What does it means? How can I understand this book better? Thanks.

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• Using MS Anti XSS library for sanitizing HTML

  - by user102533

  In the intent of preventing XSS attacks, I am updating a page in which we have a textbox that accepts HTML, stores it in a database and retrieves and renders it at a later time. My understanding is that I can sanitize the HTML using AntiXSS.GetSafeHtmlFragment() method. As long as I do this before storing the HTML in the database, am I covered? Do I need to do anything when the HTML is outputted on a web page? Also, it appears that the white list is kind of a black box. Is there a way to update this based on our requirements?

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