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  • Parallelism in Python

    - by fmark
    What are the options for achieving parallelism in Python? I want to perform a bunch of CPU bound calculations over some very large rasters, and would like to parallelise them. Coming from a C background, I am familiar with three approaches to parallelism: Message passing processes, possibly distributed across a cluster, e.g. MPI. Explicit shared memory parallelism, either using pthreads or fork(), pipe(), et. al Implicit shared memory parallelism, using OpenMP. Deciding on an approach to use is an exercise in trade-offs. In Python, what approaches are available and what are their characteristics? Is there a clusterable MPI clone? What are the preferred ways of achieving shared memory parallelism? I have heard reference to problems with the GIL, as well as references to tasklets. In short, what do I need to know about the different parallelization strategies in Python before choosing between them?

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  • iPhone OS: Strategies for high density image work

    - by Jasconius
    I have a project that is coming around the bend this summer that is going to involve, potentially, an extremely high volume of image data for display. We are talking hundreds of 640x480-ish images in a given application session (scaled to a smaller resolution when displayed), and handfuls of very large (1280x1024 or higher) images at a time. I've already done some preliminary work and I've found that the typical 640x480ish image is just a shade under 1MB in memory when placed into a UIImageView and displayed... but the very large images can be a whopping 5+ MB's in some cases. This project is actually be targeted at the iPad, which, in my Instruments tests seems to cap out at about 80-100MB's of addressable physical memory. Details aside, I need to start thinking of how to move huge volumes of image data between virtual and physical memory while preserving the fluidity and responsiveness of the application, which will be high visibility. I'm probably on the higher ends of intermediate at Objective-C... so I am looking for some solid articles and advice on the following: 1) Responsible management of UIImage and UIImageView in the name of conserving physical RAM 2) Merits of using CGImage over UIImage, particularly for the huge images, and if there will be any performance gain 3) Anything dealing with memory paging particularly as it pertains to images I will epilogue by saying that the numbers I have above maybe off by about 10 or 15%. Images may or may not end up being bundled into the actual app itself as opposed to being loaded in from an external server.

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  • Will the values of label and its correspondences change if Image is rotated?

    - by Vinayak Agarwal
    Hi all I have an image in which a text like "VINAYAK 123" is written. The text in the image is at a certain angle, say 30degrees. Now when I extract the labels of the connected components, I get V-1, I-2, N-3, A-4,Y-5,A-6,K-7, 1-8,2-9,3-10( Format: Character- Label No.). Now I rotate the image 30 degrees in the clockwise direction to make the text in the image horizontal. My question is that now if I extract the labels of the connected components, will the character and the label no. correspondence still remain the same? Thanks in advance!

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  • Video match anlysis

    - by Mohammad
    Hi every body I am looking forward to find an algorithm to detect a pattern in a given video file. Actually I am going to index moments in a tennis match video at which service (first kick after a goal) is shot. PS1: sorry for broken English. PS2: I DO NOT know anything about tennis except that you need a ball to play!!

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  • How do you composite an image onto another image with PIL in Python?

    - by Sebastian
    I need to take an image and place it onto a new, generated white background in order for it to be converted into a downloadable desktop wallpaper. So the process would go: 1) Generate new, all white image with 1440x900 dimensions 2) Place existing image on top, centered 3) Save as single image In PIL, I see the ImageDraw object, but nothing indicates it can draw existing image data onto another image. Suggestions or links anyone can recommend?

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  • how to remove a few lines from a Unicode registry file using batch commands in Windows?

    - by Cosmin
    Hi. I have a program who's generating some data in registry. I save it with "reg export HKCU\Software\ProgramName\Data data.reg" (Unicode format). I need to take it to other computer and import it there so the program from that computer could use the data. But I have to remove some text lines from data.reg. The text lines are easy to find because they contain some strings. Now I'm doing this manually (using Wordpad) every few days but maybe there is another way... Oh and I can't install other programs on these computers (the access is restricted) so I have to use batch/cmd files. What I tried so far: - redirecting the export to "con" but is visual only not in a variable; - using "for /F ..." but this works only with ANSI and removes blank lines. Can somebody please help me...? Thank you.

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  • Generating a scalogram of a signal

    - by Goz
    Hi there, I'm trying to build a scalogram view for my app to see whether there is relevant information we can retrieve from a wavelet transform as opposed to using a spectograms to see what can be retrieved via an FFT. So far I can take a wave form and I can perform the forward wavelet transform on it. However I am lost at the next step. How do I turn this information into power/energy information? I have a set of wave forms at different frequencies but I have, as I say, no frequency information. Can anyone tell me what the next step is for turning this transformed data into a scalogram? Any help would be much appreciated because my google skills are failing me!

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  • Arduino wireless options

    - by user541597
    I am currently working on a wireless solution for my arduino and computer. I am trying to connect a Transmitter to my computer and a receiver to my arduino. I have seen a lot of examples with arduino to arduino communication but none for computer to arduino. What would I need to interface the transmitter with my computer, PIC? If anyone can provide any insight or any links it would be greatly appreciated. Thanks,

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  • Matlab - Propagate points orthogonally on to the edge of shape boundaries

    - by Graham
    Hi I have a set of points which I want to propagate on to the edge of shape boundary defined by a binary image. The shape boundary is defined by a 1px wide white edge. I also have the coordinates of these points stored in a 2 row by n column matrix. The shape forms a concave boundary with no holes within itself made of around 2500 points. I want to cast a ray from each point from the set of points in an orthogonal direction and detect at which point it intersects the shape boundary at. What would be the best method to do this? Are there some sort of ray tracing algorithms that could be used? Or would it be a case of taking orthogonal unit vector and multiplying it by a scalar and testing after multiplication if the end point of the vector is outside the shape boundary. When the end point of the unit vector is outside the shape, just find the point of intersection? Thank you very much in advance for any help!

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  • Solid FFmpeg wrapper for C#/.NET

    - by Lillemanden
    I have been searching the web for some time for a solid FFmpeg wrapper for C#/.NET. But I have yet to come up with something useful. I have found the following three projects, but all of them apears to be dead in early alpha stage. FFmpeg.NET ffmpeg-sharp FFLIB.NET So my question is if anyone knows of a wrapper project that is more mature? I am not looking for a full transcoding engine with job queues and more. Just a simple wrapper so I do not have to make a command line call and then parse the console output, but can make method calls and use eventlisteners for progress. And please feel free to mention any active projects, even if they are stil in the early stages.

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  • How to Use Calculated Color Values with ColorMatrix?

    - by Otaku
    I am changing color values of each pixel in an image based on a calculation. The problem is that this takes over 5 seconds on my machine with a 1000x1333 image and I'm looking for a way to optimize it to be much faster. I think ColorMatrix may be an option, but I'm having a difficult time figure out how I would get a set of pixel RGB values, use that to calculate and then set the new pixel value. I can see how this can be done if I was just modifying (multiplying, subtracting, etc.) the original value with ColorMatrix, but now how I can use the pixels returned value to use it to calculate and new value. For example: Sub DarkenPicture() Dim clrTestFolderPath = "C:\Users\Me\Desktop\ColorTest\" Dim originalPicture = "original.jpg" Dim Luminance As Single Dim bitmapOriginal As Bitmap = Image.FromFile(clrTestFolderPath + originalPicture) Dim Clr As Color Dim newR As Byte Dim newG As Byte Dim newB As Byte For x = 0 To bitmapOriginal.Width - 1 For y = 0 To bitmapOriginal.Height - 1 Clr = bitmapOriginal.GetPixel(x, y) Luminance = ((0.21 * (Clr.R) + (0.72 * (Clr.G)) + (0.07 * (Clr.B))/ 255 newR = Clr.R * Luminance newG = Clr.G * Luminance newB = Clr.B * Luminance bitmapOriginal.SetPixel(x, y, Color.FromArgb(newR, newG, newB)) Next Next bitmapOriginal.Save(clrTestFolderPath + "colorized.jpg", ImageFormat.Jpeg) End Sub The Luminance value is the calculated one. I know I can set ColorMatrix's M00, M11, M22 to 0, 0, 0 respectively and then put a new value in M40, M41, M42, but that new value is calculated based of a value multiplication and addition of that pixel's components (((0.21 * (Clr.R) + (0.72 * (Clr.G)) + (0.07 * (Clr.B)) and the result of that - Luminance - is multiplied by the color component). Is this even possible with ColorMatrix?

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  • Perl Parallel::ForkManager wait_all_children() takes excessively long time

    - by zhang18
    I have a script that uses Parallel::ForkManager. However, the wait_all_children() process takes incredibly long time even after all child-processes are completed. The way I know is by printing out some timestamps (see below). Does anyone have any idea what might be causing this (I have 16 CPU cores on my machine)? my $pm = Parallel::ForkManager->new(16) for my $i (1..16) { $pm->start($i) and next; ... do something within the child-process ... print (scalar localtime), " Process $i completed.\n"; $pm->finish(); } print (scalar localtime), " Waiting for some child process to finish.\n"; $pm->wait_all_children(); print (scalar localtime), " All processes finished.\n"; Clearly, I'll get the Waiting for some child process to finish message first, with a timestamp of, say, 7:08:35. Then I'll get a list of Process i completed messages, with the last one at 7:10:30. However, I do not receive the message All Processes finished until 7:16:33(!). Why is that 6-minute delay between 7:10:30 and 7:16:33? Thx!

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  • Image coding library

    - by Dmitry
    Is there any good library for lossless image encoding/decoding that has compression rate more or less similar to PNG but decoding to raw RGB bitmap data would be much faster than PNG? Also alpha transparency is needed, but not essential because, alpha channel could be taken from separate image. Original problem lies in slowness of reading and decoding PNG files on iPhone using standard libraries. Obvious and the simples solution would have been storing raw RGB bitmap data, but then size of unpacked ipa is too large - 4 times larger than PNG files. So, I am trying to find some compromise solution.

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  • PHP Video Editing and Streaming

    - by Gaurav Padia
    Hi, I am developing online video streaming website on PHP. I need two functionalities: Need to add title/text at bottom of the video dynamically. Need to add background music to video dynamically. Is it possible with PHP or any available open source library? Can anyone guide me or provide links to this type of library ? Thanks.

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  • php gdlib angle problem

    - by creativz
    I'm using php gd lib 5.2.13 and tried to make a picture with imagettftext ($image, $color and $font are defined of course). imagettftext($image, 12, 90, 10, 20, $black, $font, "This.is_a test 123"); //image, font size, angle, x value, y value, color, font, text As you can see I want the angle to be 90°. The problem is that the text is not beeing rotated properly, e.g. the dots are at the top (and not at the bottom) of the text. I read that this is a common issue and has been fixed in php gdlib 5.3, But since I have 5.2.13 running on a webhost (...) is there a solution to rotate it properly with using gdlib 5.2.13? Thanks!

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  • Is their an optimal config/format for a TIFF when using Tesseract or other OCR?

    - by Zando
    I'm having a bizarre problem with Tesseract. I have a name, "Janice" that is in a 200x40 pixel tiff, that Tesseract interprets as a blank. I'm running hundreds of names through Tesseract and they are processed fine. What I'm actually doing, though, is breaking up a larger TIFF into smaller tiffs of one word each. In the larger TIFF, tesseract recognizes "Janice". What could cause it to hiccup in a TIFF that solely contains that word (and there's enough space around the word to not truncate any of the pixels)? I'm using ImageMagick to split the big TIFF, are there options I should set when reconstituting the new TIFF files?

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  • Good library to load images of different formats

    - by codymanix
    Hi Iam developing an image viewer application just like irfan-view or acdsee which should be capable to view lots of different image file formats (not just the standard ones which can be done with System.Drawing.Image). Iam currently using ImageMagick but it isn't very fast and seems to be unstable with some image files. Can anyone suggest a good imaging library, ideally with a .NET wrapper already present?

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  • Parallel.For maintain input list order on output list

    - by romeozor
    I'd like some input on keeping the order of a list during heavy-duty operations that I decided to try to do in a parallel manner to see if it boosts performance. (It did!) I came up with a solution, but since this was my first attempt at anything parallel, I'd need someone to slap my hands if I did something very stupid. There's a query that returns a list of card owners, sorted by name, then by date of birth. This needs to be rendered in a table on a web page (ASP.Net WebForms). The original coder decided he would construct the table cell-by-cell (TableCell), add them to rows (TableRow), then each row to the table. So no GridView, allegedly its performance is bad, but the performance was very poor regardless :). The database query returns in no time, the most time is spent on looping through the results and adding table cells etc. I made the following method to maintain the original order of the list: private TableRow[] ComposeRows(List<CardHolder> queryResult) { int queryElementsCount = queryResult.Count(); // array with the query's size var rowArray = new TableRow[queryElementsCount]; Parallel.For(0, queryElementsCount, i => { var row = new TableRow(); var cell = new TableCell(); // various operations, including simple ones such as: cell.Text = queryResult[i].Name; row.Cells.Add(cell); // here I'm adding the current item to it's original index // to maintain order in the output list rowArray[i] = row; }); return rowArray; } So as you can see, because I'm returning a very different type of data (List<CardHolder> -> TableRow[]), I can't just simply omit the ordering from the original query to do it after the operations. Also, I also thought it would be a good idea to Dispose() the objects at the end of each loop, because the query can return a huge list and letting cell and row objects pile up in the heap could impact performance.(?) How badly did I do? Does anyone have a better solution in case mine is flawed?

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  • Technique to remove common words(and their plural versions) from a string

    - by Jake M
    I am attempting to find tags(keywords) for a recipe by parsing a long string of text. The text contains the recipe ingredients, directions and a short blurb. What do you think would be the most efficient way to remove common words from the tag list? By common words, I mean words like: 'the', 'at', 'there', 'their' etc. I have 2 methodologies I can use, which do you think is more efficient in terms of speed and do you know of a more efficient way I could do this? Methodology 1: - Determine the number of times each word occurs(using the library Collections) - Have a list of common words and remove all 'Common Words' from the Collection object by attempting to delete that key from the Collection object if it exists. - Therefore the speed will be determined by the length of the variable delims import collections from Counter delim = ['there','there\'s','theres','they','they\'re'] # the above will end up being a really long list! word_freq = Counter(recipe_str.lower().split()) for delim in set(delims): del word_freq[delim] return freq.most_common() Methodology 2: - For common words that can be plural, look at each word in the recipe string, and check if it partially contains the non-plural version of a common word. Eg; For the string "There's a test" check each word to see if it contains "there" and delete it if it does. delim = ['this','at','them'] # words that cant be plural partial_delim = ['there','they',] # words that could occur in many forms word_freq = Counter(recipe_str.lower().split()) for delim in set(delims): del word_freq[delim] # really slow for delim in set(partial_delims): for word in word_freq: if word.find(delim) != -1: del word_freq[delim] return freq.most_common()

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  • GD! Converting a png image to jpeg and making the alpha by default white and not black.

    - by Shawn
    I tried something like this but it just makes the background of the image white, not necessarily the alpha of the image. I wanted to just upload everything as jpg's so if i could somehow "flatten" a png image with some transparently to default it to just be white so i can use it as a jpg instead. Appreciate any help. Thanks. $old = imagecreatefrompng($upload); $background = imagecolorallocate($old,255,255,255); imagefill($old, 0, 0, $background); imagealphablending($old, false); imagesavealpha($old, true);

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