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  • What is the "task" in twitter Storm parallelism

    - by John Wang
    I'm trying to learn twitter storm by following the great article "Understanding the parallelism of a Storm topology" However I'm a bit confused by the concept of "task". Is a task an running instance of the component(spout or bolt) ? A executor having multiple tasks actually is saying the same component is executed for multiple times by the executor, am I correct ? Moreover in a general parallelism sense, Storm will spawn a dedicated thread(executor) for a spout or bolt, but what is contributed to the parallelism by an executor(thread) having multiple tasks ? I think having multiple tasks in a thread, since a thread executes sequentially, only make the thread a kind of "cached" resource, which avoids spawning new thread for next task run. Am I correct? I may clear those confusion by myself after taking more time to investigate, but you know, we both love stackoverflow ;-) Thanks in advance.

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  • Cepstral Analysis for pitch detection

    - by Ohmu
    Hi! I'm looking to extract pitches from a sound signal. Someone on IRC just explain to me how taking a double FFT achieves this. Specifically: take FFT take log of square of absolute value (can be done with lookup table) take another FFT take absolute value I am attempting this using vDSP I can't understand how I didn't come across this technique earlier. I did a lot of hunting and asking questions; several weeks worth. More to the point, I can't understand why I didn't think of it. I am attempting to achieve this with vDSP library. it looks as though it has functions to handle all of these tasks. However, I'm wondering about the accuracy of the final result. I have previously used a technique which scours the frequency bins of a single FFT for local maxima. when it encounters one, it uses a cunning technique (the change in phase since the last FFT) to more accurately place the actual peak within the bin. I am worried that this precision will be lost with this technique I'm presenting here. I guess the technique could be used after the second FFT to get the fundamental accurately. But it kind of looks like the information is lost in step 2. as this is a potentially tricky process, could someone with some experience just look over what I'm doing and check it for sanity? also, I've heard there is an alternative technique involving fitting a quadratic over neighbouring bins. Is this of comparable accuracy? if so, I would favour it, as it doesn't involve remembering bin phases. so questions: does this approach makes sense? Can it be improved? I'm a bit worried about And the log square component; there seems to be a vDSP function to do exactly that: vDSP_vdbcon however, there is no indication it precalculates a log-table -- I assume it doesn't, as the FFT function requires an explicit pre-calculation function to be called and passed into it. and this function doesn't. Is there some danger of harmonics being picked up? is there any cunning way of making vDSP pull out the maxima, biggest first? Can anyone point me towards some research or literature on this technique? the main question: is it accurate enough? Can the accuracy be improved? I have just been told by an expert that the accuracy IS INDEED not sufficient. Is this the end of the line? Pi PS I get SO annoyed (npi) when I want to create tags, but cannot. :| I have suggested to the maintainers that SO keep track of attempted tags, but I'm sure I was ignored. we need tags for vDSP, accelerate framework, cepstral analysis

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  • What is the Simplest Possible Payment Gateway to Implement? (using Django)

    - by b14ck
    I'm developing a web application that will require users to either make one time deposits of money into their account, or allow users to sign up for recurring billing each month for a certain amount of money. I've been looking at various payment gateways, but most (if not all) of them seem complex and difficult to get working. I also see no real active Django projects which offer simple views for making payments. Ideally, I'd like to use something like Amazon FPS, so that I can see online transaction logs, refund money, etc., but I'm open to other things. I just want the EASIEST possible payment gateway to integrate with my site. I'm not looking for anything fancy, whatever does the job, and requires < 10 hours to get working from start to finish would be perfect. I'll give answer points to whoever can point out a good one. Thanks!

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  • looping through variable post vars and adding them to the database

    - by Neil Hickman
    I have been given the task of devising a custom forms manager that has a mysql backend. The problem I have now encountered after setting up all the front end, is how to process a form that is dynamic. For E.G Form one could contain 6 fields all with different name attributes in the input tag. Form two could contain 20 fields all with different name attributes in the input tag. How would i process the forms without using up oodles of resource.

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  • python multiprocess update dictionary synchronously

    - by user1050325
    I am trying to update one common dictionary through multiple processes. Could you please help me find out what is the problem with this code? I get the following output: inside function {1: 1, 2: -1} comes here inside function {1: 0, 2: 2} comes here {1: 0, 2: -1} Thanks. from multiprocessing import Lock, Process, Manager l= Lock() def computeCopyNum(test,val): l.acquire() test[val]=val print "inside function" print test l.release() return a=dict({1: 0, 2: -1}) procs=list() for i in range(1,3): p = Process(target=computeCopyNum, args=(a,i)) procs.append(p) p.start() for p in procs: p.join() print "comes here" print a

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  • simple process rollback question

    - by OckhamsRazor
    hi folks! while revising for an exam, i came across this simple question asking about rollbacks in processes. i understand how rollbacks occur, but i need some validation on my answer. The question: my confusion results from the fact that there is interprocess communication between the processes. does that change anything in terms of where to rollback? my answer would be R13, R23, R32 and R43. any help is greatly appreciated! thanks!

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  • What is the best way to detect white color?

    - by dnul
    I'm trying to detect white objects in a video. The first step is to filter the image so that it leaves only white-color pixels. My first approach was using HSV color space and then checking for high level of VAL channel. Here is the code: //convert image to hsv cvCvtColor( src, hsv, CV_BGR2HSV ); cvCvtPixToPlane( hsv, h_plane, s_plane, v_plane, 0 ); for(int x=0;x<srcSize.width;x++){ for(int y=0;y<srcSize.height;y++){ uchar * hue=&((uchar*) (h_plane->imageData+h_plane->widthStep*y))[x]; uchar * sat=&((uchar*) (s_plane->imageData+s_plane->widthStep*y))[x]; uchar * val=&((uchar*) (v_plane->imageData+v_plane->widthStep*y))[x]; if((*val>170)) *hue=255; else *hue=0; } } leaving the result in the hue channel. Unfortunately, this approach is very sensitive to lighting. I'm sure there is a better way. Any suggestions?

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  • Parallelizing some LINQ to XML

    - by Lol coder
    How can I make this code run in parallel? List<Crop> crops = new List<Crop>(); //Get up to 10 pages of data. for (int i = 1; i < 10; i++) { //i is basically used for paging. XDocument document = XDocument.Load(string.Format(url, i)); crops.AddRange(from c in document.Descendants("CropType") select new Crop { //The data here. }); }

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  • what is problem in the following matlab codes

    - by raju
    img=imread('img27.jpg'); %function rectangle=rect_test(img) % edge detection [gx,gy]=gradient(img); gx=abs(gx); gy=abs(gy); g=gx+gy; g=abs(g); % make it 300x300 img=zeros(300); s=size(g); img(1:s(1),1:s(2))=g; figure; imagesc((img)); colormap(gray); title('Edge detection') % take the dct of the image IM=abs(dct2(img)); figure; imagesc((IM)); colormap(gray); title('DCT') % normalize m=max(max(IM)); IM2=IM./m*100; % get rid of the peak size_IM2=size(IM2); IM2(1:round(.05*size_IM2(1)),1:round(.05*size_IM2(2))) = 0; % threshold L=length( find(IM2>20)) ; if( L > 60 ) ret = 1; else ret = 0; end

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  • Django Photologue - use photo with original compression

    - by 123
    hi, I´m uploading photos with Django Photologue. Is it possible to leave the jpgs as the are? Even if I tell photosize to use Highest Quality compression the files end up having half as many kb as the originals. I must admit that the visable loss of quality is small but as i am a photographer i would like the images to apear exactly as i edited them (photoshop). I don´t need any of photosize´s cropping and effects tools. Can it be turned off completely? thanks for your answers.

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  • How to scale JPEG images with a non-standard sampling factor in Java?

    - by HRJ
    I am using Java AWT for scaling a JPEG image, to create thumbnails. The code works fine when the image has a normal sampling factor ( 2x2,1x1,1x1 ) However, an image which has this sampling factor ( 1x1, 1x1, 1x1 ) creates problem when scaled. The colors get corrupted though the features are recognizable. The original and the thumbnail: The code I am using is roughly equivalent to: static BufferedImage awtScaleImage(BufferedImage image, int maxSize, int hint) { // We use AWT Image scaling because it has far superior quality // compared to JAI scaling. It also performs better (speed)! System.out.println("AWT Scaling image to: " + maxSize); int w = image.getWidth(); int h = image.getHeight(); float scaleFactor = 1.0f; if (w > h) scaleFactor = ((float) maxSize / (float) w); else scaleFactor = ((float) maxSize / (float) h); w = (int)(w * scaleFactor); h = (int)(h * scaleFactor); // since this code can run both headless and in a graphics context // we will just create a standard rgb image here and take the // performance hit in a non-compatible image format if any Image i = image.getScaledInstance(w, h, hint); image = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB); Graphics2D g = image.createGraphics(); g.drawImage(i, null, null); g.dispose(); i.flush(); return image; } (Code courtesy of this page ) Is there a better way to do this? Here's a test image with sampling factor of [ 1x1, 1x1, 1x1 ].

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  • How to scale JPEG image down so that text is clear as possible?

    - by Juha Syrjälä
    I have some JPEG images that I need scale down to about 80% of original size. Original image dimension are about 700px × 1000px. Images contain some computer generated text and possibly some graphics (similar to what you would find in corporate word documents). How to scale image so that the text is as legible as possible? Currently we are scaling the imaeg down using bicubic interpolation, but that makes the text blurry and foggy.

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  • Can anyone recommend a decent tool for optimising images other than photoshop

    - by toomanyairmiles
    Can anyone recommend a decent tool for optimising images other than adobe photoshop, the gimp etc? I'm looking to optimise images for the web preferably online and free. Basically I have a client who can't install additional software on their work PC but needs to optimise photographs and other images for their website and is presently uploading 1 or 2 Mb files. On a personal level I'm interested to see what other people are using...

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  • "A generic error occurred in GDI+" error while showing uploaded images

    - by Prasad
    i am using the following code to show the image that has been saved in my database from my asp.net mvc(C#) application:. public ActionResult GetSiteHeaderLogo() { SiteHeader _siteHeader = new SiteHeader(); Image imgImage = null; long userId = Utility.GetUserIdFromSession(); if (userId > 0) { _siteHeader = this.siteBLL.GetSiteHeaderLogo(userId); if (_siteHeader.Logo != null && _siteHeader.Logo.Length > 0) { byte[] _imageBytes = _siteHeader.Logo; if (_imageBytes != null) { using (System.IO.MemoryStream imageStream = new System.IO.MemoryStream(_imageBytes)) { imgImage = Image.FromStream(imageStream); } } string sFileExtension = _siteHeader.FileName.Substring(_siteHeader.FileName.IndexOf('.') + 1, _siteHeader.FileName.Length - (_siteHeader.FileName.IndexOf('.') + 1)); Response.ContentType = Utility.GetContentTypeByExtension(sFileExtension.ToLower()); Response.Cache.SetCacheability(HttpCacheability.NoCache); Response.BufferOutput = false; if (imgImage != null) { ImageFormat _imageFormat = Utility.GetImageFormat(sFileExtension.ToLower()); imgImage.Save(Response.OutputStream, _imageFormat); imgImage.Dispose(); } } } return new EmptyResult(); } It works fine when i upload original image. But when i upload any downloaded images, it throws the following error: System.Runtime.InteropServices.ExternalException: A generic error occurred in GDI+. System.Runtime.InteropServices.ExternalException: A generic error occurred in GDI+. at System.Drawing.Image.Save(Stream stream, ImageCodecInfo encoder, EncoderParameters encoderParams) at System.Drawing.Image.Save(Stream stream, ImageFormat format) For. Ex: When i upload the original image, it shows as logo in my site and i downloaded that logo from the site and when i re-upload the same downloaded image, it throws the above error. It seems very weird to me and not able to find why its happening. Any ideas on this?

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