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• Displaying Fourier transforms in OpenCV

  - by Simonw

  Hi, I'm just learning to use OpenCV and am having a problem with using DFT. I've done a signal processing class which used MatLab, so I'm trying to go through some of the exercises we did in that class. I'm trying to get and display the FT of an image, so I can mask some of the frequencies. I'd like to be able to see the FT, so I know how big to make the mask, but when I tried, I got an image like this: rather than like one of these Am I forgetting a step somewhere? I'm loading the image, converting its type to CV_32FC1, getting the matrix of it, getting the DFT, and then getting turning the resulting matrix back into an image. I'll post the code I'm using if it will be of any help? Or if someone has a link to an example of displaying the FT? I could only find ones which used it for the convolution. EDIT: Did I get the Phase of the image?

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• F# performance in scientific computing

  - by aaa

  hello. I am curious as to how F# performance compares to C++ performance? I asked a similar question with regards to Java, and the impression I got was that Java is not suitable for heavy numbercrunching. I have read that F# is supposed to be more scalable and more performant, but how is this real-world performance compares to C++? specific questions about current implementation are: How well does it do floating-point? Does it allow vector instructions how friendly is it towards optimizing compilers? How big a memory foot print does it have? Does it allow fine-grained control over memory locality? does it have capacity for distributed memory processors, for example Cray? what features does it have that may be of interest to computational science where heavy number processing is involved? Are there actual scientific computing implementations that use it? Thanks

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• How to paint fully transparent pixels/points in P2D mode?

  - by netzwerg

  According to the Processing Reference, stroke(gray, alpha) allows to set the color and opacity of the stroke. With the default color mode, an alpha value of 255 denotes full opacity, while a value of 0 should correspond to complete transparency. While this works with the (default) JAVA2D renderer, I can't seem to paint fully transparent points in P2D mode. This code clearly renders a pixel at the center of the canvas, even though the alpha value is set to 0 (fully transparent): public class Transparency extends PApplet { @Override public void setup() { size(200, 200, P2D); } @Override public void draw() { stroke(0, 0); point(width / 2, height / 2); } public static void main(String[] args) { PApplet.main(new String[] { Transparency.class.getSimpleName() }); } } What's wrong here?

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• Image 8-connectivity without excessive branching?

  - by shoosh

  I'm writing a low level image processing algorithm which needs to do alot of 8-connectivity checks for pixels. For every pixel I often need to check the pixels above it, below it and on its sides and diagonals. On the edges of the image there are special cases where there are only 5 or 3 neighbors instead of 8 neighbors for a pixels. The naive way to do it is for every access to check if the coordinates are in the right range and if not, return some default value. I'm looking for a way to avoid all these checks since they introduce a large overhead to the algorithm. Are there any tricks to avoid it altogether?

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• Running Awk command on a cluster

  - by alex

  How do you execute a Unix shell command (awk script, a pipe etc) on a cluster in parallel (step 1) and collect the results back to a central node (step 2) Hadoop seems to be a huge overkill with its 600k LOC and its performance is terrible (takes minutes just to initialize the job) i don't need shared memory, or - something like MPI/openMP as i dont need to synchronize or share anything, don't need a distributed VM or anything as complex Google's SawZall seems to work only with Google proprietary MapReduce API some distributed shell packages i found failed to compile, but there must be a simple way to run a data-centric batch job on a cluster, something as close as possible to native OS, may be using unix RPC calls i liked rsync simplicity but it seem to update remote notes sequentially, and you cant use it for executing scripts as afar as i know switching to Plan 9 or some other network oriented OS looks like another overkill i'm looking for a simple, distributed way to run awk scripts or similar - as close as possible to data with a minimal initialization overhead, in a nothing-shared, nothing-synchronized fashion Thanks Alex

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• Need PHP Email Script Solution

  - by JCHASE11

  Designing forms has always been fun, but getting them to send email on the server side is another story. I have used various email scripts (dynaform,phpmailer, etc), and have experienced a ton of problems. So here is the site I am working on: Contact On the Right. It is very basic: no validation, no required fields. I simply need anything that is entered to be sent back to me. Does anyone know of any BASIC PHP form processing scripts, or have a few lines of code that would work here? I'm not a PHP guy, so I am struggling! Thanks in advance.

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• How to use DoG Pyramid in SIFT

  - by Ahmet Keskin

  Hi all, I am very new in image processing and pattern recognition. I am trying to implement SIFT algorithm where I am able to create the DoG pyramid and identify the local maximum or minimum in each octave. What I don't understand is that how to use these local max/min in each octave. How do I combine these points? My question may sound very trivial. I have read Lowe's paper, but could not really understand what he did after he built the DoG pyramid. Any help is appreciated. Thank you

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• How do I create an OpenCV image from a PIL image?

  - by scrible

  I want to do some image processing with OpenCV (in Python), but I have to start with a PIL Image object, so I can't use the cvLoadImage() call, since that takes a filename. This recipe (adapted from http://opencv.willowgarage.com/wiki/PythonInterface) does not work because cvSetData complains argument 2 of type 'void *' . Any ideas? from opencv.cv import * from PIL import Image pi = Image.open('foo.png') # PIL image ci = cvCreateImage(pi.size, IPL_DEPTH_8U, 1) # OpenCV image data = pi.tostring() cvSetData(ci, data, len(data)) I think the last argument to the cvSetData is wrong too, but I am not sure what it should be.

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• Browser Side Photo Editing Library

  - by echox

  Hi! Currently I'm searching for a free solution to simple edit some photos at the users browser. Resizing and Cropping would be mandatory. I'm not searching for an online service (for example SUMO or PIXLR which are great), because I want to include the software into a WYSIWYG Editor. JavaScript would be really nice, but it would have to work in IE 8. Pixastic is a great example, but works only in modern browsers (not IE 8 :-/) Any suggestions what I could use? Maybe setting up some kind of image processing service with ImageMagick and communicating with it through AJAX could also be an solution? Has anyone gained some experience with such a solution?

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• Making Overlaid image transparent on touch in Android ?

  - by Andhravaala

  Hi All, I need help on making the touched areas of bitmap image transparent(seems like erasing) while I am moving my finger on that image. I am having a PNG file with Alpha channel in it. I want to turn the touched pixels to transparent so that, the user can feel that he is actually erasing it. For this I am using frame layout to load 2 layers. Down layer is for content and upper layer is an Imageview for erasing. I need erase the upper layer when user touch and move his finger on it. I am not getting how to make it transparent. can anyone please help me in this. If possible please direct me to any sample code, as I am very new to this image processing. Thanks in advance.

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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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• Plotting Points in Java with Interaction

  - by mellort

  I have a large number of data points which are two dimensional coordinates with non-integer values (floats). I am looking for a Java library that can help me plot these points, allowing for custom point size, color, and labels. Further, I would like the user to be able to interact with the points with panning and zooming, and I want to be able to capture KeyEvents from the user. Processing looks great for what I want, but I don't want to do everything from scratch. Is there a better solution? Thanks in advance.

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• Erlang message loops

  - by Roger Alsing

  How does message loops in erlang work, are they sync when it comes to processing messages? As far as I understand, the loop will start by "receive"ing a message and then perform something and hit another iteration of the loop. So that has to be sync? right? If multiple clients send messages to the same message loop, then all those messages are queued and performed one after another, or? To process multiple messages in parallell, you would have to spawn multiple message loops in different processes, right? Or did I misunderstand all of it?

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• Physical Cores vs Virtual Cores in Parallelism

  - by Code Curiosity

  When it comes to virtualization, I have been deliberating on the relationship between the physical cores and the virtual cores, especially in how it effects applications employing parallelism. For example, in a VM scenario, if there are less physical cores than there are virtual cores, if that's possible, what's the effect or limits placed on the application's parallel processing? I'm asking, because in my environment, it's not disclosed as to what the physical architecture is. Is there still much advantage to parallelizing if the application lives on a dual core VM hosted on a single core physical machine?

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• Bash: any command to replace strings in text files?

  - by mikez302

  I have a hierarchy of directories containing many text files. I would like to search for a particular text string every time it comes up in one of the files, and replace it with another string. For example, I may want to replace every occurrence of the string "Coke" with "Pepsi". Does anyone know how to do this? I am wondering if there is some sort of Bash command that can do this without having to load all these files in an editor, or come up with a more complex script to do it. I found this page explaining a trick using sed, but it doesn't seem to work in files in subdirectories.

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• Image analysis on the iPhone

  - by user362808

  Hi, guys! Hopefully a quick one. Working on a devious little algorithm that'll automatically scan a user's iPhone for a photo of some emotional poignance (e.g. go back in time a ways, look for one of a group of photos that are proximally timestamped, etc.). Need a quick-and-dirty way of picking out a photo containing two people in close proximity to each other. I know that the OpenCV Python lib [for image processing] works on the iPhone, I'm just curious whether it's actually the best way of doing this (from scratch or otherwise). Cheers!

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• Background subtracting in MATLAB

  - by eiphyomin

  I'm looking to do background subtracting on an image. I'm new to MATLAB and new to image processing/analysis, so sorry if any of this sounds stupid. 1) Other than imsubtract() are there other ways to do background subtracting (besides comparing one image to another)? 2) In the Math Works explanation for imsubtract() why do they make their structuring element a disk? This seems rather difficult so far because every time I try something, I end up not only subtracting the noisy background but also losing the parts of the image I want to look at!

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• Forcing a mixed ISO-8859-1 and UTF-8 multi-line string into UTF-8 in Perl

  - by knorv

  Consider the following problem: A multi-line string $junk contains some lines which are encoded in UTF-8 and some in ISO-8859-1. I don't know a priori which lines are in which encoding, so heuristics will be needed. I want to turn $junk into pure UTF-8 with proper re-encoding of the ISO-8859-1 lines. Also, in the event of errors in the processing I want to provide a "best effort result" rather than throwing an error. My current attempt looks like this: $junk = &force_utf8($junk); sub force_utf8 { my $input = shift; my $output = ''; foreach my $line (split(/\n/, $input)) { if (utf8::valid($line)) { utf8::decode($line); } $output .= "$line\n"; } return $output; } While this appears to work I'm certain this is not the optimal solution. How would you improve the force_utf8(...) sub?

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• List of uninteresting words

  - by Hooked

  [Caveat] This is not directly a programing question, but it is something that comes up so often in language processing that I'm sure it's of some use to the community. Does anyone have a good list of uninteresting (English) words that have been tested by more then a casual look? This would include all prepositions, conjunctions, etc... words that may have semantic meaning, but are often frequent in every sentence, regardless of the subject. I've built my own lists from time to time for personal projects but they've been ad-hoc; I continuously add words that I forgotten as they come in.

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• Take advantage of multiple cores executing SQL statements

  - by willvv

  I have a small application that reads XML files and inserts the information on a SQL DB. There are ~ 300 000 files to import, each one with ~ 1000 records. I started the application on 20% of the files and it has been running for 18 hours now, I hope I can improve this time for the rest of the files. I'm not using a multi-thread approach, but since the computer I'm running the process on has 4 cores I was thinking on doing it to get some improvement on the performance (although I guess the main problem is the I/O and not only the processing). I was thinking on using the BeginExecutingNonQuery() method on the SqlCommand object I create for each insertion, but I don't know if I should limit the max amount of simultaneous threads (nor I know how to do it). What's your advice to get the best CPU utilization? Thanks

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• How would you find the height of objects given an image?

  - by Ram Bhat

  Heyguys.. This isn't exactly a programming question exactly. I just want to know what your approach would be to a common problem in Digital image processing. Lets say you have an image of a a few trees in say jpg format. How would you go about finding the heights of each of these trees. The photo is the only input you have. I want to know the approaches you have not code. So it doesnt matter if your answers are vague, or non DIP-ish.

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• How do I make complex SQL queries easier to write?

  - by DragonLord

  I'm finding it very difficult to write complex SQL queries involving joins across many (at least 3-4) tables and involving several nested conditions. The queries I'm being asked to write are easily described by a few sentences, but can require a deceptive amount of code to complete. I'm finding myself often using temporary views to write these queries, which seem like a bit of a crutch. What tips can you provide that I can use to make these complex queries easier? More specifically, how do I break these queries down into the steps I need to use to actually write the SQL code? Note that I'm the SQL I'm being asked to write is part of homework assignments for a database course, so I don't want software that will do the work for me. I want to actually understand the code I'm writing. More technical details: The database is hosted on a PostgreSQL server running on the local machine. The database is very small: there are no more than seven tables and the largest table has less than about 50 rows. The SQL queries are being passed unchanged to the server, via LibreOffice Base.

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• C# using the "this" keyword in this situation?

  - by Alex

  Hi, I've completed a OOP course assignment where I design and code a Complex Number class. For extra credit, I can do the following: Add two complex numbers. The function will take one complex number object as a parameter and return a complex number object. When adding two complex numbers, the real part of the calling object is added to the real part of the complex number object passed as a parameter, and the imaginary part of the calling object is added to the imaginary part of the complex number object passed as a parameter. Subtract two complex numbers. The function will take one complex number object as a parameter and return a complex number object. When subtracting two complex numbers, the real part of the complex number object passed as a parameter is subtracted from the real part of the calling object, and the imaginary part of the complex number object passed as a parameter is subtracted from the imaginary part of the calling object. I have coded this up, and I used the this keyword to denote the current instance of the class, the code for my add method is below, and my subtract method looks similar: public ComplexNumber Add(ComplexNumber c) { double realPartAdder = c.GetRealPart(); double complexPartAdder = c.GetComplexPart(); double realPartCaller = this.GetRealPart(); double complexPartCaller = this.GetComplexPart(); double finalRealPart = realPartCaller + realPartAdder; double finalComplexPart = complexPartCaller + complexPartAdder; ComplexNumber summedComplex = new ComplexNumber(finalRealPart, finalComplexPart); return summedComplex; } My question is: Did I do this correctly and with good style? (using the this keyword)?

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• Remove image background with csharp or a .net component

  - by Homer1980ar

  I'm trying to find some info about removing an image background "automagically" if possible with csharp or a .NET component. Actually I could not find much data and I don't event know if it's possible or are there any API components available. Any ideas? Thanks, Leonardo

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• Remove image solid background with c sharp

  - by Homer1980ar

  I'm trying to find some info about removing an image background "automagically" if possible in .NET. Actually I could not find much data and I don't event know if it's possible or are there any API components available. Any ideas?

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