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  • Problem with "write" function in linux

    - by Dumitru Catalin
    I am trying to write 2 server/client programs under Linux, in which they communicate through named pipes. The problem is that sometimes when I try to write from the server into a pipe that doesn't exist anymore (the client has stopped), I get a "Resource temporarily unavailable" error and the server stops completely. I understand that this is caused by using a O_NONBLOCK parameter when opening the fifo chanel, indicating the point where the program would usually wait until it could write again in the file, but is there a way to stop this behavior, and not halt the entire program if a problem occurs (shouldn't the write command return -1 ad the program continue normally)? And another strange thing is that this error only occurs when running the programs outside the ide (eclipse). If I run both programs inside eclipse, on error the write function just returns -1 and the programs continues normally.

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  • Java Executor: Small tasks or big ones?

    - by Arash Shahkar
    Consider one big task which could be broken into hundreds of small, independently-runnable tasks. To be more specific, each small task is to send a light network request and decide upon the answer received from the server. These small tasks are not expected to take longer than a second, and involve a few servers in total. I have in mind two approaches to implement this using the Executor framework, and I want to know which one's better and why. Create a few, say 5 to 10 tasks each involving doing a bunch of send and receives. Create a single task (Callable or Runnable) for each send & receive and schedule all of them (hundreds) to be run by the executor. I'm sorry if my question shows that I'm lazy to test these and see for myself what's better (at least performance-wise). My question, while looking after an answer to this specific case, has a more general aspect. In situations like these when you want to use an executor to do all the scheduling and other stuff, is it better to create lots of small tasks or to group those into a less number of bigger tasks?

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  • ScheduledThreadPoolExecutor executing a wrong time because of CPU time discrepancy

    - by richs
    I'm scheduling a task using a ScheduledThreadPoolExecutor object. I use the following method: public ScheduledFuture<?> schedule(Runnable command, long delay,TimeUnit unit) and set the delay to 30 seconds (delay = 30,000 and unit=TimeUnit.MILLISECONDS). Sometimes my task occurs immediately and other times it takes 70 seconds. I believe the ScheduledThreadPoolExecutor uses CPU specific clocks. When i run tests comparing System.currentTimeMillis(), System.nanoTime() [which is CPU specific] i see the following schedule: 1272637682651ms, 7858346157228410ns execute: 1272637682667ms, 7858386270968425ns difference is 16ms but 4011374001ns (or 40,113ms) so it looks like there is discrepancy between two CPU clocks of 40 seconds How do i resolve this issue in java code? Unfortunately this is a clients machine and i can't modify their system.

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  • Invalid Cross-Thread Operations from BackgroundWorker2_RunWorkerCompleted in C#

    - by Jim Fell
    Hello. I'm getting an error that does not make sense. Cross-thread operation not valid: Control 'buttonOpenFile' accessed from a thread other than the thread it was created on. In my application, the UI thread fires off backgroundWorker1, which when almost complete fires off backgroundWorker2 and waits for it to complete. backgroundWorker1 waits for backgroundWorker2 to complete, before it completes. AutoResetEvent variables are used to flag when each of the workers complete. In backgroundWorker2_RunWorkerComplete a function is called that resets the form controls. It is in this ResetFormControls() function where the exception is thrown. I thought it was safe to modify form controls in the RunWorkerCompleted function. Both background workers are instantiated from the UI thread. Here is a greatly summarized version of what I am doing: AutoResetEvent evtProgrammingComplete_c = new AutoResetEvent(false); AutoResetEvent evtResetComplete_c = new AutoResetEvent(false); private void ResetFormControls() { toolStripProgressBar1.Enabled = false; toolStripProgressBar1.RightToLeftLayout = false; toolStripProgressBar1.Value = 0; buttonInit.Enabled = true; buttonOpenFile.Enabled = true; // Error occurs here. buttonProgram.Enabled = true; buttonAbort.Enabled = false; buttonReset.Enabled = true; checkBoxPeripheryModule.Enabled = true; checkBoxVerbose.Enabled = true; comboBoxComPort.Enabled = true; groupBoxToolSettings.Enabled = true; groupBoxNodeSettings.Enabled = true; } private void buttonProgram_Click(object sender, EventArgs e) { while (backgroundWorkerProgram.IsBusy) backgroundWorkerProgram.CancelAsync(); backgroundWorkerProgram.RunWorkerAsync(); } private void backgroundWorkerProgram_DoWork(object sender, DoWorkEventArgs e) { // Does a bunch of stuff... if (tProgramStat_c == eProgramStat_t.DONE) { tProgramStat_c = eProgramStat_t.RESETTING; while (backgroundWorkerReset.IsBusy) backgroundWorkerReset.CancelAsync(); backgroundWorkerReset.RunWorkerAsync(); evtResetComplete_c.WaitOne(LONG_ACK_WAIT * 2); if (tResetStat_c == eResetStat_t.COMPLETED) tProgramStat_c = eProgramStat_t.DONE; } } private void backgroundWorkerProgram_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) { // Updates form to report complete. No problems here. evtProgrammingComplete_c.Set(); backgroundWorkerProgram.Dispose(); } private void backgroundWorkerReset_DoWork(object sender, DoWorkEventArgs e) { // Does a bunch of stuff... if (tResetStat_c == eResetStat_t.COMPLETED) if (tProgramStat_c == eProgramStat_t.RESETTING) evtProgrammingComplete_c.WaitOne(); } private void backgroundWorkerReset_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) { CloseAllComms(); ResetFormControls(); evtResetComplete_c.Set(); backgroundWorkerReset.Dispose(); } Any thoughts or suggestions you may have would be appreciated. I am using Microsoft Visual C# 2008 Express Edition. Thanks.

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  • ArrayBlockingQueue exceeds given capacity

    - by Wojciech Reszelewski
    I've written program solving bounded producer & consumer problem. While constructing ArrayBlockingQueue I defined capacity 100. I'm using methods take and put inside threads. And I've noticed that sometimes I see put 102 times with any take's between them. Why does it happen? Producer run method: public void run() { Object e = new Object(); while(true) { try { queue.put(e); } catch (InterruptedException w) { System.out.println("Oj, nie wyszlo, nie bij"); } System.out.println("Element added"); } } Consumer run method: public void run() { while(true) { try { queue.take(); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("Element removed"); } } Part of uniq -c on file with output: 102 Element removed 102 Element added 102 Element removed 102 Element added 102 Element removed 102 Element added 102 Element removed 102 Element added 102 Element removed 102 Element added 102 Element removed 102 Element added 2 Element removed 2 Element added 102 Element removed 102 Element added

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  • Find messages from certain key till certain key while being able to remove stale keys.

    - by Alfred
    My problem Let's say I add messages to some sort of datastructure: 1. "dude" 2. "where" 3. "is" 4. "my" 5. "car" Asking for messages from index[4,5] should return: "my","car". Next let's assume that after a while I would like to purge old messages because they aren't useful anymore and I want to save memory. Let's say at time x messages[1-3] became stale. I assume that it would be most efficient to just do the deletion once every x seconds. Next my datastructure should contain: 4. "my" 5. "car" My solution? I was thinking of using a concurrentskiplistset or concurrentskiplist map. Also I was thinking of deleting the old messages from inside a newSingleThreadScheduledExecutor. I would like to know how you would implement(efficiently/thread-safe) this or maybe use a library?

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  • Long primitive or AtomicLong for a counter?

    - by Rich
    Hi I have a need for a counter of type long with the following requirements/facts: Incrementing the counter should take as little time as possible. The counter will only be written to by one thread. Reading from the counter will be done in another thread. The counter will be incremented regularly (as much as a few thousand times per second), but will only be read once every five seconds. Precise accuracy isn't essential, only a rough idea of the size of the counter is good enough. The counter is never cleared, decremented. Based upon these requirements, how would you choose to implement your counter? As a simple long, as a volatile long or using an AtomicLong? Why? At the moment I have a volatile long but was wondering whether another approach would be better. I am also incrementing my long by doing ++counter as opposed to counter++. Is this really any more efficient (as I have been led to believe elsewhere) because there is no assignment being done? Thanks in advance Rich

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  • Benchmarks for Single and MultiThreaded programs

    - by user280848
    Hi I am trying to compare the performance of Single and Multithreaded Java programs. Are there any single thread benchmarks which are available which I could then use and convert to their multithreaded version and compare the performance. Could anybody guide me as to what kind of programs(not very small) are suitable for this empirical comparison. Thanks in advance

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  • Why thread started by ScheduledExecutorService.schedule() never quits?

    - by moonese
    If I create a scheduled task by calling ScheduledExecutorService.schedule(), it never quits after execution, is it a JDK bug, or I just miss something? note: doSomething() is empty method below. public static void doSomething() { } public static void main(String[] args) { ScheduledFuture scheduleFuture = Executors.newSingleThreadScheduledExecutor().schedule(new Callable() { public Void call() { try { doSomething(); } catch (Exception e) { e.printStackTrace(); } return null; } }, 1, TimeUnit.SECONDS); }

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  • Java Thread wait() => blocked?

    - by Chris
    According to http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Thread.State.html calling wait() will result a thread to go in BLOCKED state. However this piece of code will result (after being called) in a Thread in WAITING State. class bThread extends Thread { public synchronized void run() { try { wait(); } catch (InterruptedException e) { e.printStackTrace(); } } } Have I got something wrong? Can anybody explain this behaviour to me? Any help would be appreciated!

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  • Vmware software installation error

    - by Perry
    I am trying to install Vmware software, but I am facing the following error: Selecting previously unselected package vmware-view-client:i386. (Reading database ... 239594 files and directories currently installed.) Unpacking vmware-view-client:i386 (from .../vmware-view-client_2.1.0-0ubuntu0.12.04_i386.deb) ... Processing triggers for desktop-file-utils ... Processing triggers for bamfdaemon ... Rebuilding /usr/share/applications/bamf.index... Processing triggers for gnome-menus ... Setting up icaclient:i386 (12.1.0) ... dpkg: error processing icaclient:i386 (--configure): subprocess installed post-installation script returned error exit status 2 Setting up vmware-view-client:i386 (2.1.0-0ubuntu0.12.04) ... Processing triggers for libc-bin ... ldconfig deferred processing now taking place Errors were encountered while processing: icaclient:i386 E: Sub-process /usr/bin/dpkg returned an error code (1) A package failed to install. Trying to recover: Setting up icaclient:i386 (12.1.0) ... dpkg: error processing icaclient:i386 (--configure): subprocess installed post-installation script returned error exit status 2 Errors were encountered while processing: icaclient:i386 Any suggestions on how to fix this issue? Thanks in advance

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  • Error when I try to installth desktop integration features for Openoffice

    - by PENG TENG
    peng@peng-ThinkPad-SL410:~$ cd '/home/peng/Downloads/en-US/DEBS/desktop-integration' peng@peng-ThinkPad-SL410:~/Downloads/en-US/DEBS/desktop-integration$ sudo dpkg -i *.deb (Reading database ... 357248 files and directories currently installed.) Unpacking openoffice.org-debian-menus (from openoffice.org3.4-debian-menus_3.4-9593_all.deb) ... dpkg: error processing openoffice.org3.4-debian-menus_3.4-9593_all.deb (--install): trying to overwrite '/usr/bin/soffice', which is also in package libreoffice-common 1:3.6.2~rc2-0ubuntu3 /usr/bin/gtk-update-icon-cache gtk-update-icon-cache: Cache file created successfully. /usr/bin/gtk-update-icon-cache gtk-update-icon-cache: Cache file created successfully. Processing triggers for menu ... Processing triggers for hicolor-icon-theme ... Processing triggers for gnome-icon-theme ... Processing triggers for shared-mime-info ... Unknown media type in type 'all/all' Unknown media type in type 'all/allfiles' Unknown media type in type 'uri/mms' Unknown media type in type 'uri/mmst' Unknown media type in type 'uri/mmsu' Unknown media type in type 'uri/pnm' Unknown media type in type 'uri/rtspt' Unknown media type in type 'uri/rtspu' Processing triggers for bamfdaemon ... Rebuilding /usr/share/applications/bamf.index... Processing triggers for desktop-file-utils ... Processing triggers for gnome-menus ... Errors were encountered while processing: openoffice.org3.4-debian-menus_3.4-9593_all.deb Can anyone solve the problem?

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  • Eigenvector computation using OpenCV

    - by Andriyev
    Hi I have this matrix A, representing similarities of pixel intensities of an image. For example: Consider a 10 x 10 image. Matrix A in this case would be of dimension 100 x 100, and element A(i,j) would have a value in the range 0 to 1, representing the similarity of pixel i to j in terms of intensity. I am using OpenCV for image processing and the development environment is C on Linux. Objective is to compute the Eigenvectors of matrix A and I have used the following approach: static CvMat mat, *eigenVec, *eigenVal; static double A[100][100]={}, Ain1D[10000]={}; int cnt=0; //Converting matrix A into a one dimensional array //Reason: That is how cvMat requires it for(i = 0;i < affnDim;i++){ for(j = 0;j < affnDim;j++){ Ain1D[cnt++] = A[i][j]; } } mat = cvMat(100, 100, CV_32FC1, Ain1D); cvEigenVV(&mat, eigenVec, eigenVal, 1e-300); for(i=0;i < 100;i++){ val1 = cvmGet(eigenVal,i,0); //Fetching Eigen Value for(j=0;j < 100;j++){ matX[i][j] = cvmGet(eigenVec,i,j); //Fetching each component of Eigenvector i } } Problem: After execution I get nearly all components of all the Eigenvectors to be zero. I tried different images and also tried populating A with random values between 0 and 1, but the same result. Few of the top eigenvalues returned look like the following: 9805401476911479666115491135488.000000 -9805401476911479666115491135488.000000 -89222871725331592641813413888.000000 89222862280598626902522986496.000000 5255391142666987110400.000000 I am now thinking on the lines of using cvSVD() which performs singular value decomposition of real floating-point matrix and might yield me the eigenvectors. But before that I thought of asking it here. Is there anything absurd in my current approach? Am I using the right API i.e. cvEigenVV() for the right input matrix (my matrix A is a floating point matrix)? cheers

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  • Gmagick extension for php install -- how and where?

    - by Vivek Chandra
    Downloaded php-pear and tried installing gmagick extension by following the steps given in link "http://www.gerd-riesselmann.net/development/how-install-imagick-and-gmagick-ubuntu" The pecl gave an error -- gmagick-1.0.9b1$ pecl install gmagick Failed to download pecl/gmagick within preferred state "stable", latest release is version 1.0.9b1, stability "beta", use "channel://pecl.php.net/gmagick-1.0.9b1" to install install failed Tried adding the channel (no result)-- gmagick-1.0.9b1$ pecl channel-add http://pecl.php.net/package/gmagick/1.0.9b1 Error: No version number found in tag channel-add: invalid channel.xml file Found the link "http://pecl.php.net/package/gmagick" to download the php extension untar'd it to find the following files -- gmagick-1.0.9b1$ ls config.m4 gmagickdraw_methods.c gmagick_methods.c LICENSE php_gmagick_helpers.h README gmagick.c gmagick_helpers.c gmagickpixel_methods.c php_gmagick.h php_gmagick_macros.h Tried . / config.m4 only to find more errors gmagick-1.0.9b1$ . / config.m4 ./config.m4: line 1: syntax error near unexpected token `gmagick,' ./config.m4: line 1: `PHP_ARG_WITH(gmagick, whether to enable the gmagick extension,' Been at this since a day with no result.Read that gmagick is a swiss knife of image processing,sad that there isnt much documentation done on it or at least a proper how to install link anywhere. Badly need help. Thanks in advance.

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  • Using regex to extract variables from a plain-text form letter?

    - by Yaaqov
    Hi - I'm looking for a good example of using Regular Expressions in PHP to "reverse engineer" a form letter (with a known format, of course) that has been pasted into a multiline textbox and sent to a script for processing. So, for example, let's assume this is the original plain-text input (taken from a USDA press release): WASHINGTON, April 5, 2010 - North American Bison Co-Op, a New Rockford, N.D., establishment is recalling approximately 25,000 pounds of whole beef heads containing tongues that may not have had the tonsils completely removed, which is not compliant with regulations that require the removal of tonsils from cattle of all ages, the U.S. Department of Agriculture's Food Safety and Inspection Service (FSIS) announced today. For clarity, the fields that are variables are highlighted below: [pr_city=]WASHINGTON, [pr_date=]April 5, 2010 - [corp_name=]North American Bison Co-Op, a [corp_city=]New Rockford, [corp_state=]N.D., establishment is recalling approximately [amount=]25,000 pounds of [product=]whole beef heads containing tongues that may not have had the tonsils completely removed, which is not compliant with regulations that require [reason=]the removal of tonsils from cattle of all ages, the U.S. Department of Agriculture's Food Safety and Inspection Service (FSIS) announced today. How could I efficiently extract the contents of the pr_city pr_date corp_name corp_city corp_state amount product reason fields from my example? Any help would be appreciated, thanks.

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  • How to do recurring with bank account payment mode using authorized.net

    - by Salil
    Hi All, I am using recurring facility of authorized.net using active_merchant plugin in rails. there are two payment method for this 1] Credit Card 2] Bank Account I successfully done it using Credit Card For Recurring i need my Test Mode off. Also my E-check, credit card processing, and subscriptions are all enabled. But i am not able to subscribed using Bank Account Following is my code ActiveMerchant::Billing::Base.mode = :developer #i found follwing test bank account on net account = ActiveMerchant::Billing::Check.new(:account_holder_type=>"personal",:account_number=>"123123123", :account_type => "savings", :name=>"name", :routing_number=>"244183602") if account.valid? #this comes true gateway = ActiveMerchant::Billing::AuthorizeNetGateway.new(:login => 'Mylogin', :password => 'Mypassword') response = gateway.recurring( amount, nil, {:interval =>{:length=>@length, :unit =>:months}, :duration =>{:start_date=>'2010-04-24', :occurrences=>1}, :billing_address=>{:first_name=>'dinesh', :last_name=>'singh'}, :bank_account=>{:account_holder_type=>"personal",:account_number=>"123123123", :account_type => "savings", :name_of_account=>"name", :routing_number=>"244183602"} }) if response.success? #this comes false else puts response.message ####>> ERROR render :action=>"account_payment" end I get Follwing ERROR when i debug for response.message "The test transaction was not successful. (128) This transaction cannot be processed." Am i doing anything wrong i search for the another Test Bank Account Data but i didn't find it. Please help I badly need it. Thanks in Advance. Regards, Salil Gaikwad

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  • What is the most efficient way to display decoded video frames in Qt?

    - by Jason
    What is the fastest way to display images to a Qt widget? I have decoded the video using libavformat and libavcodec, so I already have raw RGB or YCbCr 4:2:0 frames. I am currently using a QGraphicsView with a QGraphicsScene object containing a QGraphicsPixmapItem. I am currently getting the frame data into a QPixmap by using the QImage constructor from a memory buffer and converting it to QPixmap using QPixmap::fromImage(). I like the results of this and it seems relatively fast, but I can't help but think that there must be a more efficient way. I've also heard that the QImage to QPixmap conversion is expensive. I have implemented a solution that uses an SDL overlay on a widget, but I'd like to stay with just Qt since I am able to easily capture clicks and other user interaction with the video display using the QGraphicsView. I am doing any required video scaling or colorspace conversions with libswscale so I would just like to know if anyone has a more efficient way to display the image data after all processing has been performed. Thanks.

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  • Verizon SongID - How is it programmed?

    - by CheeseConQueso
    For anyone not familiar with Verizon's SongID program, it is a free application downloadable through Verizon's VCast network. It listens to a song for 10 seconds at any point during the song and then sends this data to some all-knowing algorithmic beast that chews it up and sends you back all the ID3 tags (artist, album, song, etc...) The first two parts and last part are straightforward, but what goes on during the processing after the recorded sound is sent? I figure it must take the sound file (what format?), parse it (how? with what?) for some key identifiers (what are these? regular attributes of wave functions? phase/shift/amplitude/etc), and check it against a database. Everything I find online about how this works is something generic like what I typed above. From audiotag.info This service is based on a sophisticated audio recognition algorithm combining advanced audio fingerprinting technology and a large songs' database. When you upload an audio file, it is being analyzed by an audio engine. During the analysis its audio “fingerprint” is extracted and identified by comparing it to the music database. At the completion of this recognition process, information about songs with their matching probabilities are displayed on screen.

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  • Patterns for non-layered applications

    - by Paul Stovell
    In Patterns of Enterprise Application Architecture, Martin Fowler writes: This book is thus about how you decompose an enterprise application into layers and how those layers work together. Most nontrivial enterprise applications use a layered architecture of some form, but in some situations other approaches, such as pipes and filters, are valuable. I don't go into those situations, focussing instead on the context of a layered architecture because it's the most widely useful. What patterns exist for building non-layered applications/parts of an application? Take a statistical modelling engine for a financial institution. There might be a layer for data access, but I expect that most of the code would be in a single layer. Would you still expect to see Gang of Four patterns in such a layer? How about a domain model? Would you use OO at all, or would it be purely functional? The quote mentions pipes and filters as alternate models to layers. I can easily imagine a such an engine using pipes as a way to break down the data processing. What other patterns exist? Are there common patterns for areas like task scheduling, results aggregation, or work distribution? What are some alternatives to MapReduce?

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  • Temporary storage for keeping data between program iterations?

    - by mr.b
    I am working on an application that works like this: It fetches data from many sources, resulting in pool of about 500,000-1,500,000 records (depends on time/day) Data is parsed Part of data is processed in a way to compare it to pre-existing data (read from database), calculations are made, and stored in database. Resulting dataset that has to be stored in database is, however, much smaller in size (compared to original data set), and ranges from 5,000-50,000 records. This process almost always updates existing data, perhaps adds few more records. Then, data from step 2 should be kept somehow, somewhere, so that next time data is fetched, there is a data set which can be used to perform calculations, without touching pre-existing data in database. I should point out that this data can be lost, it's not irreplaceable (key information can be read from database if needed), but it would speed up the process next time. Application components can (and will be) run off different computers (in the same network), so storage has to be reachable from multiple hosts. I have considered using memcached, but I'm not quite sure should I do so, because one record is usually no smaller than 200 bytes, and if I have 1,500,000 records, I guess that it would amount to over 300 MB of memcached cache... But that doesn't seem scalable to me - what if data was 5x that amount? If it were to consume 1-2 GB of cache only to keep data in between iterations (which could easily happen)? So, the question is: which temporary storage mechanism would be most suitable for this kind of processing? I haven't considered using mysql temporary tables, as I'm not sure if they can persist between sessions, and be used by other hosts in network... Any other suggestion? Something I should consider?

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  • Bilinear interpolation - DirectX vs. GDI+

    - by holtavolt
    I have a C# app for which I've written GDI+ code that uses Bitmap/TextureBrush rendering to present 2D images, which can have various image processing functions applied. This code is a new path in an application that mimics existing DX9 code, and they share a common library to perform all vector and matrix (e.g. ViewToWorld/WorldToView) operations. My test bed consists of DX9 output images that I compare against the output of the new GDI+ code. A simple test case that renders to a viewport that matches the Bitmap dimensions (i.e. no zoom or pan) does match pixel-perfect (no binary diff) - but as soon as the image is zoomed up (magnified), I get very minor differences in 5-10% of the pixels. The magnitude of the difference is 1 (occasionally 2)/256. I suspect this is due to interpolation differences. Question: For a DX9 ortho projection (and identity world space), with a camera perpendicular and centered on a textured quad, is it reasonable to expect DirectX.Direct3D.TextureFilter.Linear to generate identical output to a GDI+ TextureBrush filled rectangle/polygon when using the System.Drawing.Drawing2D.InterpolationMode.Bilinear setting? For this (magnification) case, the DX9 code is using this (MinFilter,MipFilter set similarly): Device.SetSamplerState(0, SamplerStageStates.MagFilter, (int)TextureFilter.Linear); and the GDI+ path is using: g.InterpolationMode = InterpolationMode.Bilinear; I thought that "Bilinear Interpolation" was a fairly specific filter definition, but then I noticed that there is another option in GDI+ for "HighQualityBilinear" (which I've tried, with no difference - which makes sense given the description of "added prefiltering for shrinking") Followup Question: Is it reasonable to expect pixel-perfect output matching between DirectX and GDI+ (assuming all external coordinates passed in are equal)? If not, why not? Finally, there are a number of other APIs I could be using (Direct2D, WPF, GDI, etc.) - and this question generally applies to comparing the output of "equivalent" bilinear interpolated output images across any two of these. Thanks!

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  • Assemble an image browser side with JavaScript or Flash?

    - by Kris Walker
    Would it be possible to assemble an image on the browser by 'concatenating' other downloaded images together? The use case is this. The page will display 36 different tiles (small images). The user should be able to arrange those tiles into a 6 x 6 grid and save the resulting grid to disk as an image. The best solution would be to do it all in the browser without Flash. The next best solution would be to allow the user to create the grid in the browser with simple JavaScript drag and drop functionality and then send the coordinates to the server for image processing. The last solution would be to do it all in the browser with Flash. Is it even possible for Flash to create an image and then allow the user to save it from the browser? I am familiar with the Pixastic JavaScript library ( http://www.pixastic.com/ ), but it relies on getting image data to and from a canvas element which is not very well supported. What if I send the tile images to the browser as base64 encoded strings? Could I use JavaScript to create the 6 x 6 grid image? And if so, is there some way of allowing the user to get it onto disk without relying on the canvas element?

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  • How to handle alpha in a manual "Overlay" blend operation?

    - by quixoto
    I'm playing with some manual (walk-the-pixels) image processing, and I'm recreating the standard "overlay" blend. I'm looking at the "Photoshop math" macros here: http://www.nathanm.com/photoshop-blending-math/ (See also here for more readable version of Overlay) Both source images are in fairly standard RGBA (8 bits each) format, as is the destination. When both images are fully opaque (alpha is 1.0), the result is blended correctly as expected: But if my "blend" layer (the top image) has transparency in it, I'm a little flummoxed as to how to factor that alpha into the blending equation correctly. I expect it to work such that transparent pixels in the blend layer have no effect on the result, opaque pixels in the blend layer do the overlay blend as normal, and semitransparent blend layer pixels have some scaled effect on the result. Can someone explain to me the blend equations or the concept behind doing this? Bonus points if you can help me do it such that the resulting image has correctly premultiplied alpha (which only comes into play for pixels that are not opaque in both layers, I think.) Thanks! // factor in blendLayerA, (1-blendLayerA) somehow? resultR = ChannelBlend_Overlay(baseLayerR, blendLayerR); resultG = ChannelBlend_Overlay(baseLayerG, blendLayerG); resultB = ChannelBlend_Overlay(baseLayerB, blendLayerB); resultA = 1.0; // also, what should this be??

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  • Using Matlab to find maxima for data with a lot of noise

    - by jimbo
    I have noisy data set with three peaks in Matlab and want to do some image processing on it. The peaks are about 5-9 pixels wide at the base, in a 50 x 50 array. How do I locate the peaks? Matlab is very new to me. Here is what I have so far... For my original image, let's call it "array", I tried J = fspecial('gaussian',[5 5], 1.5); C = imfilter(array, J) peaks = imregionalmax(C); but there is still some noise along the baseline between the peaks so I end up getting a ton of local max that are really just noise values. (I tried playing with the size of the filter, but that didn't help.) I also tried peaks = imextendedmax(C,threshold); where the threshold was determined visually... which works but is definitely not a good way to do it since it's not that robust obviously. So, how do I locate these peaks in a robust way? Thanks.

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