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• Resizing an image with alpha channel

  - by Hafthor

  I am writing some code to generate images - essentially I have a source image that is large and includes transparent regions. I use GDI+ to open that image and add additional objects. What I want to do next is to save this new image much smaller, so I used the Bitmap constructor that takes a source Image object and a height and width, then saved that. I was expecting the alpha channel to be smoothed like the color channels, but this did not happen -- it did result in a couple of semitransparent pixels, but overall it is very blocky. What gives? Using img As New Bitmap("source100x100.png") ''// Drawing stuff Using simg As New Bitmap(img, 20, 20) simg.Save("target20x20.png") End Using End Using Edit: I think what I want is SuperSampling, like what Paint.NET does when set to "Best Quality"

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• Handling Corrupted JPEGs in C#

  - by ddango

  We have a process that pulls images from a remote server. Most of the time, we're good to go, the images are valid, we don't timeout, etc. However, every once and awhile we see this error similar to this: Unhandled Exception: System.Runtime.InteropServices.ExternalException: A generic error occurred in GDI+. at System.Drawing.Image.Save(Stream stream, ImageCodecInfo encoder, EncoderPa rameters encoderParams) at ConsoleApplication1.Program.Main(String[] args) in C:\images\ConsoleApplic ation1\ConsoleApplication1\Program.cs:line 24 After not being able to reproduce it locally, we looked closer at the image, and realized that there were artifacts, making us suspect corruption. Created an ugly little unit test with only the image in question, and was unable to reproduce the error on Windows 7 as was expected. But after running our unit test on Windows Server 2008, we see this error every time. Is there a way to specify non-strictness for jpegs when writing them? Some sort of check/fix we can use? Unit test snippet: var r = ReadFile("C:\\images\\ConsoleApplication1\\test.jpg"); using (var imgStream = new MemoryStream(r)) { using (var ms = new MemoryStream()) { var guid = Guid.NewGuid(); var fileName = "C:\\images\\ConsoleApplication1\\t" + guid + ".jpg"; Image.FromStream(imgStream).Save(ms, ImageFormat.Jpeg); using (FileStream fs = File.Create(fileName)) { fs.Write(ms.GetBuffer(), 0, ms.GetBuffer().Length); } } }

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• How do I use graythresh on an indexed image in MATLAB?

  - by user198729

  I = imread('coins.png'); level = graythresh(I); BW = im2bw(I,level); imshow(BW) The above is an example from the MATLAB documentation using a grayscale image. How can I make it work with an indexed image like in this post?

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• How to implement async pattern in windows forms application?

  - by Alkersan

  I'm using an MVC pattern in winforms application. I need to call remote service asynchronously. So On some event in View I invoke corresponding Presenter method. In Presenter I call BeginInvoke method of service. But to View must be updated only in Main Thread. I could actualy point CallBack to some function in View, and update it`s controls state, but this conflicts with MVP pattern - View must not be responsible for data it carries. This callback function must be in Presenter. But how then invoke View in Main Thread?

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• How to obtain histogram for RGB image

  - by gavishna

  I have an image say lena_color.tif and i want to see the histogram for it without converting it to gray.i tries with hist3,but its not working. Plz help

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• Resize image on upload php

  - by blasteralfred

  Hi, I have a php script for image upload as below <?php $LibID = $_POST[name]; define ("MAX_SIZE","10000"); function getExtension($str) { $i = strrpos($str,"."); if (!$i) { return ""; } $l = strlen($str) - $i; $ext = substr($str,$i+1,$l); return $ext; } $errors=0; $image=$_FILES['image']['name']; if ($image) { $filename = stripslashes($_FILES['image']['name']); $extension = getExtension($filename); $extension = strtolower($extension); if (($extension != "jpg") && ($extension != "jpeg")) { echo '<h1>Unknown extension!</h1>'; $errors=1; exit(); } else { $size=filesize($_FILES['image']['tmp_name']); if ($size > MAX_SIZE*1024) { echo '<h1>You have exceeded the size limit!</h1>'; $errors=1; exit(); } $image_name=$LibID.'.'.$extension; $newname="uimages/".$image_name; $copied = copy($_FILES['image']['tmp_name'], $newname); if (!$copied) { echo '<h1>image upload unsuccessfull!</h1>'; $errors=1; exit(); }}} ?> which uploads the image file to a folder "uimages" in the root. I have made changes in the html file for the compact display of the image by defining "max-height" and "max-width". But i want to resize the image file on upload. The image file may have a maximum width of 100px and maximum height of 150px. The image proportions must be constrained. That is, the image may be smaller than the above dimensions, but, it should not exceed the limit. How can I make this possible?? Thanks in advance :) blasteralfred..

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• Why does using the Asynchronous Programming Model in .Net not lead to StackOverflow exceptions?

  - by uriDium

  For example, we call BeginReceive and have the callback method that BeginReceive executes when it has completed. If that callback method once again calls BeginReceive in my mind it would be very similar to recursion. How is that this does not cause a stackoverflow exception. Example code from MSDN: private static void Receive(Socket client) { try { // Create the state object. StateObject state = new StateObject(); state.workSocket = client; // Begin receiving the data from the remote device. client.BeginReceive( state.buffer, 0, StateObject.BufferSize, 0, new AsyncCallback(ReceiveCallback), state); } catch (Exception e) { Console.WriteLine(e.ToString()); } } private static void ReceiveCallback( IAsyncResult ar ) { try { // Retrieve the state object and the client socket // from the asynchronous state object. StateObject state = (StateObject) ar.AsyncState; Socket client = state.workSocket; // Read data from the remote device. int bytesRead = client.EndReceive(ar); if (bytesRead > 0) { // There might be more data, so store the data received so far. state.sb.Append(Encoding.ASCII.GetString(state.buffer,0,bytesRead)); // Get the rest of the data. client.BeginReceive(state.buffer,0,StateObject.BufferSize,0, new AsyncCallback(ReceiveCallback), state); } else { // All the data has arrived; put it in response. if (state.sb.Length > 1) { response = state.sb.ToString(); } // Signal that all bytes have been received. receiveDone.Set(); } } catch (Exception e) { Console.WriteLine(e.ToString()); } }

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• How to automate the padding for arbitary images using MatLab?

  - by user198729

  This is a further question based on this answer: http://stackoverflow.com/questions/2589851/how-can-i-implement-this-visual-effect-in-matlab/2589957#2589957 The general solution should work for all background colors and length/width ratio.

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• openmp program elapsed time not scaling with increased threads

  - by Griff

  I've got this openmp fortran program doing an embarrassingly parallel problem - do loop over 512^3 elements. See output below. Why would there be such strange behavior in the elapsed time as a function of threads? I thought it would peak at a sweet spot then slowly degrade. This clearly isn't happening. Perhaps I misunderstand something about openmp. Threads, omp_get_wtime 1, 103.76298500015400 2, 65.346454000100493 4, 45.923643999965861 7, 38.074195000110194 8, 36.968765000114217 9, 39.45981499995105 10,40.753379000118002 12,39.577559999888763 14,37.909950000001118

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• Cilk or Cilk++ or OpenMP

  - by Aman Deep Gautam

  I'm creating a multi-threaded application in Linux. here is the scenario: Suppose I am having x instance of a class BloomFilter and I have some y GB of data(greater than memory available). I need to test membership for this y GB of data in each of the bloom filter instance. It is pretty much clear that parallel programming will help to speed up the task moreover since I am only reading the data so it can be shared across all processes or threads. Now I am confused about which one to use Cilk, Cilk++ or OpenMP(which one is better). Also I am confused about which one to go for Multithreading or Multiprocessing

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• Video encoding by servlet with MEncoder

  - by Andrey

  Hello. I was developing an application for video encoding on the server and got a problem with encoding video with MEncoder. This decoder doesn't work correctly when runned by a command line with Runtime.getRuntime().exec(“D:\mencoder\mnc\mencoder.exe video1.avi -o outvideo1.flv -of lavf -oac mp3lame -lameopts abr:br=64 -srate 22050 -ovc lavc -lavcopts vcodec=flv:vbitrate=300:mbd=2:mv0:trell:v4mv:cbp:last_pred=3 -vf scale=320:240,harddup -quiet”) ; The decoder launches and works in windows console with my parameters, but when it's run from a servlet it just hangs in process list and doesn't do anything before the web-server is stopped. When trying to use decoder from a simple java applcation, it runs correctly. Thanks for help.

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• How to decide between using PLINQ and LINQ at runtime?

  - by Hamish Grubijan

  Or decide between a parallel and a sequential operation in general. It is hard to know without testing whether parallel or sequential implementation is best due to overhead. Obviously it will take some time to train "the decider" which method to use. I would say that this method cannot be perfect, so it is probabilistic in nature. The x,y,z do influence "the decider". I think a very naive implementation would be to give both 1/2 chance at the beginning and then start favoring them according to past performance. This disregards x,y,z, however. I suspect that this question would be better answered by academics than practitioners. Anyhow, please share your heuristic, your experience if any, your tips on this. Sample code: public interface IComputer { decimal Compute(decimal x, decimal y, decimal z); } public class SequentialComputer : IComputer { public decimal Compute( ... // sequential implementation } public class ParallelComputer : IComputer { public decimal Compute( ... // parallel implementation } public class HybridComputer : IComputer { private SequentialComputer sc; private ParallelComputer pc; private TheDecider td; // Helps to decide between the two. public HybridComputer() { sc = new SequentialComputer(); pc = new ParallelComputer(); td = TheDecider(); } public decimal Compute(decimal x, decimal y, decimal z) { decimal result; decimal time; if (td.PickOneOfTwo() == 0) { // Time this and save result into time. result = sc.Compute(...); } else { // Time this and save result into time. result = pc.Compute(); } td.Train(time); return result; } }

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• Bandpass filter of FFT applied image. (Like ImageJ bandpass filter algorithm)

  - by maximus

  There is a good function that I need, which is implemented in Java program: ImageJ I need to understand the algorithm used there. The function has several parameters: link text And before using FFT it converts image to a special one: The Bandpass Filter uses a special algorithm to reduce edge artifacts (before the Fourier transform, the image is extended in size by attaching mirrored copies of image parts outside the original image, thus no jumps occur at the edges) Can you tell me more about this special transform? Actually tiling mirrored image. I am writing on C++ and wish to rewrite that part of the program on C++.

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• How to make a single image in to different(optimize) sizes once image uploaded?

  - by Shakil

  Hi All i am working on mvc4(webapi) i need create for single image into different sizes for example i had loaded a image for file upload control once press the button of upload the single image should divide in to different sizes (like thumbnail large size medium size ) actually i am new for webapi i don't have any idea about it but i need to make this by writing hard code i will provide a path for it to store images could any body plz help me to do this work thank in advance

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• How to convert indexed bitmap images to non-index binary bitmap and replace in place?

  - by Runner

  I'm not familiar with graphics editing software, and somehow the bitmap generated are indexed images, now I want to convert them all into non-indexed and binary version. These bitmap images are all saved in D:\images\ How to convert them all using MATLAB?

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• Thresholding in Matlab

  - by 3babala

  How do I threshold an image to find the local maxes in a robust way? I know I can just look at the data, visually guess at some appropriate h value, and do imextendedmax(I,h) where h is the threshold... but I'm looking for a more robust way to do it in Matlab. I'm pretty new to Matlab and coding so this is all foreign...

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• Detecting Markers Using OpenCV

  - by Hamza Yerlikaya

  I am trying to detect various objects containing colored markers, so a red blue green marker identifies object A, and a red blue red marker identifies object B. My problem is I can't use template matching cause objects can be rotated, currently I am thinking about check for each color then find the object by checking the distance between colors but it seems inefficient, so my question is there a better way to do this?

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• How to process audio in real time?

  - by user1756648

  I am giving some audio input through microphone. I recorded it in Audacity, it looks something like as shown below. I want to process this audio in real time. I mainly want to do this. 1) see real time audio amplitude vs time graph 2) perform some actions based on some thing (like if a specific type of hike is seen in audio, then do something, else do something else) Is there any python module or C library that can allow me to do this ?

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• Standardizing camera input in OpenCV? (Contrast/Saturation/Brightness etc..)

  - by karpathy

  I am building an application using OpenCV that uses the webcam and runs some vision algorithms. I would like to make this application available on the internet after I am done, but I am concerned about the vast differences in camera settings on every computer, and I am worried that the algorithm may break if the settings are too different from mine. Is there any way, after capturing the frame, to post process it and make sure that the contrast is X, brightness is Y, and saturation is Z? I think the Camera settings themselves can not be changed from code directly using the current OpenCV Python bindings. Would anyone be able to tell me about how I could calculate some of these parameters from the image and adjust them appropriately using OpenCV?

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• How can I implement this visual effect in MATLAB?

  - by user198729

  One can use Google's logo for a try: BTW, what's the term for it?

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• Codeigniter Image Library Cropping an Image with 2 sets of coordinates to make square anywhere?

  - by chris

  Spending time reading through the docs, and searching for examples. I understand cropping an image from top 0, and left 0 is pretty straight forward. However. I would like to pass 2 sets of coordinates, a starting point and an ending point. Four Points, a Square that is defined anywhere. However from the examples I am finding, and from what I gather the rendition is not going to let me do this. codeigniter so I am seeking confirmation on this thought, is it true that I can only provide end points from 0, and it crops a square based on said end points or can I actually specify an x start, an x end, and similar for y? Or is there some other technique I can use within codeigniter that will allow me to pass for coordinates for starting and ending points?

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• How to detect circles accurately

  - by user1767798

  Is there any way to accurately detect circles in opencv? I was using hough transform which give me good result but most of the time, shadow of the object and surrounding,light etc gives bad results, so am looking for options other than hough circles, accurate detection is very important for my project. My basic approach so far is to find some spheres in the image taken in realtime. I am using houghcircle to find the spheres and base later calculations on the radius I am getting from that. If the background is plain and nothing the sphere detect without problem, however if I am taking that image in my room where the background will have other objects it's often difficult to detect. So am looking for some other approach.

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• What's the fastest way to approximate the period of data using Octave?

  - by John

  I have a set of data that is periodic (but not sinusoidal). I have a set of time values in one vector and a set of amplitudes in a second vector. I'd like to quickly approximate the period of the function. Any suggestions? Specifically, here's my current code. I'd like to approximate the period of the vector x(:,2) against the vector t. Ultimately, I'd like to do this for lots of initial conditions and calculate the period of each and plot the result. function xdot = f (x,t) xdot(1) =x(2); xdot(2) =-sin(x(1)); endfunction x0=[1;1.75]; #eventually, I'd like to try lots of values for x0(2) t = linspace (0, 50, 200); x = lsode ("f", x0, t) plot(x(:,1),x(:,2)); Thank you! John

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• Java - Robot keyPress issue

  - by Trimbitas Sorin

  I'm trying to send keystrokes (like a virtual keyboard) from my Java code, but I encounter some issues. It works perfectly on normal applications (for example, Notepad, browsers, etc.), but not on games (fullscreen or windowed mode). This is the stripped code I'm using: import java.awt.Robot; import java.awt.AWTException; import java.awt.event.InputEvent; Robot robot; robot.keyPress(KeyEvent.VK_A); robot.keyRelease(KeyEvent.VK_A); How can this problem be fixed?

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• Auto scale and rotate images

  - by Dave Jarvis

  Given: two images of the same subject matter; the images have the same resolution, colour depth, and file format; the images differ in size and rotation; and two lists of (x, y) co-ordinates that correlate the images. I would like to know: How do you transform the larger image so that it visually aligns to the second image? (Optional.) What are the minimum number of points needed to get an accurate transformation? (Optional.) How far apart do the points need to be to get an accurate transformation? The transformation would need to rotate, scale, and possibly shear the larger image. Essentially, I want to create (or find) a program that does the following: Input two images (e.g., TIFFs). Click several anchor points on the small image. Click the several corresponding anchor points on the large image. Transform the large image such that it maps to the small image by aligning the anchor points. This would help align pictures of the same stellar object. (For example, a hand-drawn picture from 1855 mapped to a photograph taken by Hubble in 2000.) Many thanks in advance for any algorithms (preferably Java or similar pseudo-code), ideas or links to related open-source software packages.

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