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  • Simple C++ container class that is thread-safe for writing

    - by conradlee
    I am writing a multi-threaded program using OpenMP in C++. At one point my program forks into many threads, each of which need to add "jobs" to some container that keeps track of all added jobs. Each job can just be a pointer to some object. Basically, I just need the add pointers to some container from several threads at the same time. Is there a simple solution that performs well? After some googling, I found that STL containers are not thread-safe. Some stackoverflow threads address this question, but none that forms a consensus on a simple solution.

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  • How to convert a BufferedImage to 8 bit?

    - by Zach Sugano
    I was looking at the ImageConverter class, trying to figure out how to convert a BufferedImage to 8-bit color, but I have no idea how I would do this. I was also searching around the internet and I could find no simple answer, they were all talking about 8 bit grayscale images. I simply want to convert the colors of an image to 8 bit... nothing else, no resizing no nothing. Does anyone mind telling me how to do this.

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  • Linear Interpolation. How to implement this algorithm in C ? (Python version is given)

    - by psihodelia
    There exists one very good linear interpolation method. It performs linear interpolation requiring at most one multiply per output sample. I found its description in a third edition of Understanding DSP by Lyons. This method involves a special hold buffer. Given a number of samples to be inserted between any two input samples, it produces output points using linear interpolation. Here, I have rewritten this algorithm using Python: temp1, temp2 = 0, 0 iL = 1.0 / L for i in x: hold = [i-temp1] * L temp1 = i for j in hold: temp2 += j y.append(temp2 *iL) where x contains input samples, L is a number of points to be inserted, y will contain output samples. My question is how to implement such algorithm in ANSI C in a most effective way, e.g. is it possible to avoid the second loop? NOTE: presented Python code is just to understand how this algorithm works. UPDATE: here is an example how it works in Python: x=[] y=[] hold=[] num_points=20 points_inbetween = 2 temp1,temp2=0,0 for i in range(num_points): x.append( sin(i*2.0*pi * 0.1) ) L = points_inbetween iL = 1.0/L for i in x: hold = [i-temp1] * L temp1 = i for j in hold: temp2 += j y.append(temp2 * iL) Let's say x=[.... 10, 20, 30 ....]. Then, if L=1, it will produce [... 10, 15, 20, 25, 30 ...]

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  • Asynchronous SQL Operations

    - by Paul Hatcherian
    I've got a problem I'm not sure how best to solve. I have an application which updates a database in response to ad hoc requests. One request in particular is quite common. The request is an update that by itself is quite simple, but has some complex preconditions. For this request the business layer first requests a set of data from the data layer. The business logic layer evaluated the data from the database and parameters from the request, from this the action to be performed is determined, and the request's response message(s) are created. The business layer now executes the actual update command that is the purpose of the request. This last step is the problem, this command is dependent on the state of the database, which might have changed since the business logic ran. Locking down the data read in this operation across several round-trips to the database doesn't seem like a good idea either. Is there a 'best-practice' way to accomplish something like this? Thanks!

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  • Implemeting "drawing modes" in a graphics library?

    - by banister
    i would like to implement 'drawing modes' (in my own graphics library). That is drawing with AND, OR, etc However i am storing colors using floats, each channel between 0 and 1.0 Do i have to first convert each color channel to 0-255 before i can use the AND, OR, etc drawing modes? and then convert back to float (0.0-1.0) ? Or is there another way of doing it? thanks

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  • Why are Asynchronous processes not called Synchronous?

    - by Balk
    So I'm a little confused by this terminology. Everyone refers to "Asynchronous" computing as running different processes on seperate threads, which gives the illusion that these processes are running at the same time. This is not the definition of the word asynchronous. a·syn·chro·nous –adjective 1. not occurring at the same time. 2. (of a computer or other electrical machine) having each operation started only after the preceding operation is completed. What am I not understanding here?

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  • How can I compress jpeg images in Java without losing any metadata in that image?

    - by guitarpoet
    I want compress jpeg files using Java. I do it like this: Read the image as BufferedImage Write the image to another file with compression rate. OK, that seems easy, but I find the ICC color profile and the EXIF information are gone in the new file and the DPI of the image is dropped from 240 to 72. It looks different from the origin image. I use a tool like preview in OS X. It can perfectly change the quality of the image without affecting other information. Can I done this in Java? At least keep the ICC color profile and let the image color look the same as the origin photo?

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  • Automatically download files in Ruby

    - by Obinna
    I'm trying to write a ruby script which automatically downloads some files from some server ever 30-45 minutes (to prevent overload) as long as my computer is turned on. It's possible that my computer might be turned off at some point, but the download should resume (probably re-download the current file). I already have the file list but I can't figure out how to make such a script to run autonomously. What are some ways I can do this?

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  • divide the image into 3*3 blocks

    - by Jayanth Silesh
    I have a matrix that does not happen to have dimensions that are multiples of 3 or it might. How can we divide the entire image into blocks of 3*3 matrices. (Can ignore the last ones which does not come under the 3*3 multiples. Also, the 3*3 matrices can be be saved in arrays. a=3; b=3; %window size x=size(f,1)/a; y=size(f,2)/b; %f is the original image m=a*ones(1,x); n=b*ones(1,y); I=mat2cell(f,m,n);

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  • Java for loop with multiple incrementers

    - by user2517280
    Im writing a program which combines the RGB pixel values for 3 images, e.g. red pixel of image 1, green pixel of image 2 and blue pixel of image 3 and I want to then create a final image of it. Im using the code below, but this seems to be incrementing x2 and x3 whilst x1 is the same, i.e. not giving the right pixel value for same co-ordinate for each image. for (int x = 0; x < image.getWidth(); x++) { for (int x2 = 0; x2 < image2.getWidth(); x2++) { for (int x3 = 0; x3 < image3.getWidth(); x3++) { for (int y = 0; y < image.getHeight(); y++) { for (int y2 = 0; y2 < image2.getHeight(); y2++) { for (int y3 = 0; y3 < image3.getHeight(); y3++) { So I was wondering if anyone can tell me how to iterate through each of the 3 images on the same co-ordinate, so for example read 1, 1 of each image and record the red, green and blue value accordingly. Apologies if it doesnt make complete sense, its a bit hard to explain. I can iterate the values for one image fine but when I add in another, things start to go a bit wrong as obviously its quite a bit more complicated! I was thinking it might be easier to create an array and replace the according values in that just not sure how to do that effectively either. Thanks

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  • About curse of dimensionality

    - by Dan
    My question is about this topic I've been reading about a bit. Basically my understanding is that in higher dimensions all points end up being very close to each other. The doubt I have is whether this means that calculating distances the usual way (euclidean for instance) is valid or not. If it were still valid, this would mean that when comparing vectors in high dimensions, the two most similar wouldn't differ much from a third one even when this third one could be completely unrelated. Is this correct? Then in this case, how would you be able to tell whether you have a match or not?

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  • Separating text and graphics in an image

    - by avd
    I dont know whether should I post this question here or not? But if someone knows it, please answer? What are the algorithms for determining which region in an image is text and which one is graphic? Means how to separate such regions? (figure or diagram)

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  • Filtering spectrum using FIR filters

    - by Alex Hoppus
    If i have signal values x[T] and filter coefficients b[i], i can perform filtering using convolution. Suppose i have spectrum of x (after FFT) and i need to perform filtering using filters coefficients, how can i perform this? I heard that in frequency domain it will be multiplying, rather than convolution (time domain). But i can't find an equation to use it. I have 614000 values in y = fft(x[T]) vector and 119 filter coefficients (generated using fdatool), i can't multiply them directly ... Thanks.

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  • Compressing digitalized document images

    - by Adabada
    Hello, We are now required by law to digitalize all the financial documents in our company and submit them to evaluations every 3 months. Since this is sensitive data we decided to take matters into our own hands and build some sort of digital data archiver. The tool works perfectly, but after 7 months of usage we are begining to worry about the disk space used by these images. Here some info on the amount of documents digitalized: 15K documents scanned and archived per day, with final PNG size of +- 860KB: 15 000 * 860 kilobits = 1.53779984 gigabytes 30 days of work per month: 1.53779984 gigabytes * 30 = 46.1339952 gigabytes Expectation of disk space usage after 1 year: 46.1339952 gigabytes * 12 = 553.607942 gigabytes So far we're at 424 gigabytes of disk space used, without counting backup. We're using PNG as image format, but I would like to know if anyone have any advice on a better compression algorithm for images or alternative strategies for compressing the PNG's even more or even better ways to archive images as to save disk space. Any help would be appreciated, thanks.

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  • Can I use MPI_Probe to probe messsages sent by any collective operation?

    - by takwing
    In my code I have a server process repeatedly probing for incoming messages, which come in two types. One type of the two will be sent once by each process to give hint to the server process about its termination. I was wondering if it is valid to use MPI_Broadcast to broadcast these termination messages and use MPI_Probe to probe their arrivals. I tried using this combination but it failed. This failure might have been caused by some other things. So I would like anyone who knows about this to confirm. Cheers.

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  • Is there any library/software available that can give me useful measurements of image quality?

    - by Thor84no
    I realise measuring image quality in software is going to be really difficult, and I'm not looking for a quick-fix. Googling this is largely showing up research papers and discussions that go a bit over my head, so I was wondering if anyone in the SO community had any experience with doing any rough image quality assessment? I want to use this to scan a few thousand images and whittle it down to a few dozen images that are most likely of poor quality. I could then show these to a user and leave the rest to them. Obviously there are many metrics that can be a part of whether an image is of high/low quality, I'd be happy with anything that could take an image as an input and give some reasonable metrics to any of the basic image quality metrics like sharpness, dynamic range, noise, etc., leaving it up to my software to determine what's acceptable and what isn't. Some of the images are poor quality because they've been up-scaled drastically. If there isn't a way of getting metrics like I suggested above, is there any way to detect that an image has been up-scaled like this?

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  • How to play a set of jpeg files as a movie?

    - by RJ
    I have a set of jpeg images where eacg image has an associated description. e.g. im1.jpg - suspect enters bank im7.jpg - suspect hands teller a note imj41.jpg - teller gives suspect a bag ... ... It's trivial to view these images individually and see the description but how do I play this as a movie? I need to play the images and when I encounter one with a description, display the description in a status pane. Do I need to convert the images into a movie, if so how? How do I get the player to notify me when the description frame is encountered? I'm using Windows. language doesn't matter, I just need the concept right now.

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  • Reading Characher from Image

    - by Chinjoo
    I am working on an application which requires matching of numbers from a scanned image file to database entry and update the database with the match result. Say I have image- employee1.jpg. This image will have two two handwritten entries - Employee number and the amount to be paid to the employee. I have to read the employee number from the image and query the database for the that number, update the employee with the amount to be paid as got from the image. Both the employee number and amount to be paid are written inside two boxes at a specified place on the image. Is there any way to automate this. Basically I want a solution in .net using c#. I know this can be done using artificial neural networks. Any ideas would be much appreciated.

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  • Java Servlet framework that does things like rencoding images to preferred format etc.

    - by mP
    Are there any frameworks/libraries that provide servlets/filters etc that handle reencoding on the fly of images. interpret the accept headers and output the file, reencoding into the new format if necessary by checking the actual format of the original image file. provide a low and high quality version of an image. re encode an image into new dimensions. width and height parameters might query string parameters. I could create versions of the file in all the formats, at upload time but the seems overkill. I would rather lazily create the rencoded file and stick it in a cache if it gets served again etc.

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  • Best way to get photoshop to optimise 35 related pictures for fast transmission

    - by thenerd
    I have 35 pictures taken from a stationary camera aimed at a lightbox in which an object is placed, rotated at 10 degrees in each picture. If I cycle through the pictures quickly, the image looks like it is rotating. If I wished to 'rotate' the object in a browser but wanted to transmit as little data as possible for this, I thought it might be a good idea to split the picture into 36 pictures, where 1 picture is any background the images have in common, and 35 pictures minus the background, just showing the things that have changed. Do you think this approach will work? Is there a better route? How would I achieve this in photoshop?

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