**Major reason** - PNG will give you advantage of [Alpha Transparency][1] over JPG. 

Also see: https://stackoverflow.com/questions/2336522/png-vs-gif-vs-jpeg-when-best-to-use/7752936#7752936


  [1]: http://en.wikipedia.org/wiki/Alpha_compositing


PNGs are smaller for images a few solid colors (solid polygons) (because they make JPEG artifacts more obvious)
JPEGs are better for photos and other images that don&#39;t have consistent patterns (JPEG artifacts are harder to notice here)

I have a problem with these client and server codes, I keep getting the **[Errno 10061] No connection could be made because the target machine actively refused it** 

I&#39;m running the server on a virtual machine with Windows XP SP3 and the client on Windows 7 64bit, my python version is 2.7.3. What I want to know is how should I edit the code to use the client and server on different networks! Thanks! 

**server :**

    #!/usr/bin/python           # This is server.py file
 
    import socket               # Import socket module
    s = socket.socket()         # Create a socket object
    host = &#39;0.0.0.0&#39; # Get local machine name
    port = 12345                # Reserve a port for your service.
 
 
    print &#39;Server started!&#39;
    print &#39;Waiting for clients...&#39;
 
    s.bind((host, port))        # Bind to the port
    s.listen(5)                 # Now wait for client connection.
    c, addr = s.accept()     # Establish connection with client.
    print &#39;Got connection from&#39;, addr
    while True:
      msg = c.recv(1024)
      print addr, &#39; &gt;&gt; &#39;, msg
      msg = raw_input(&#39;SERVER &gt;&gt; &#39;)
      c.send(msg);
      #c.close()                # Close the connection


**client :**

    #!/usr/bin/python           # This is client.py file
 
    import socket               # Import socket module
 
    s = socket.socket()         # Create a socket object
    host = socket.gethostname() # Get local machine name
    port = 12345                # Reserve a port for your service.
 
    print &#39;Connecting to &#39;, host, port
    s.connect((host, port))
 
    while True:
      msg = raw_input(&#39;CLIENT &gt;&gt; &#39;)
      s.send(msg)
      msg = s.recv(1024)
      print &#39;SERVER &gt;&gt; &#39;, msg
    #s.close                     # Close the socket when done

PS : code is from internet.

Errno 10061 : No connection could be made because the target machine actively refused it ( client - server )

In a recent [Slashdot Interview][1] Linus Torvalds gave an example of how some people use pointers in a way that indicates they don&#39;t really understand how to use them correctly. 

Unfortunately, since I&#39;m one of the people he&#39;s talking about, I also failed to understand his example:

&gt; *I&#39;ve seen too many people who delete a singly-linked list entry by keeping track of the &quot;prev&quot; entry, and then to delete the entry, doing
&gt; something like*
&gt; 
&gt;     if (prev)
&gt;         prev-&gt;next = entry-&gt;next;
&gt;     else
&gt;         list_head = entry-&gt;next;
&gt; 
&gt; 
&gt; &lt;em&gt;and whenever I see code like that, I just go &quot;This person doesn&#39;t
&gt; understand pointers&quot;. And it&#39;s sadly quite common. People who
&gt; understand pointers just use a &quot;pointer to the entry pointer&quot;, and
&gt; initialize that with the address of the list_head. And then as they
&gt; traverse the list, they can remove the entry without using any
&gt; conditionals, by just doing&lt;/em&gt;
&gt; 
&gt;     *pp = entry-&gt;next

Can someone provide a bit more explanation about why this approach is better, and how it can work without a conditional statement?

  [1]: http://meta.slashdot.org/story/12/10/11/0030249/linus-torvalds-answers-your-questions

Using pointers to remove item from singly-linked list

I&#39;m building an app that uses a lot of images, so it&#39;s getting pretty big. I got more than 15mb in PNG images, and if I convert those images to JPG I would get 5MB or less! So, why should I use PNG instead of JPG?

I know that PNGs are preferred, but what would I lose with JPG?

EDIT: Thank you everybody!

Just a note: Since I got my answer and turns out that I will need to use PNG in most files, I found out that website http://tinypng.org/ , and that&#39;s helping me a lot. My 15mb of images are now 7mb. So, if anyone is in the same situation that I am, I hope that it helps!

Why should I use PNG and not JPG?

I'm building an app that uses a lot of images, so it's getting pretty big. I got more than 15mb in PNG images, and if I convert those images to JPG I would get 5MB or less! So, why should I use PNG instead of JPG?
I know that PNGs are preferred, but what would I lose with JPG?
EDIT: Thank you everybody!
Just a note: Since I got my answer and turns out that I will need to use PNG in most files, I found out that website <a href="http://tinypng.org/" target="_blank" rel="noopener noreferrer">http://tinypng.org/</a> , and that's helping me a lot. My 15mb of images are now 7mb. So, if anyone is in the same situation that I am, I hope that it helps!

How can we perform `Email Validation` on `edittext` in `android` ? I have gone through google &amp; SO but I didn&#39;t find out a simple way to validate it.

Email Address Validation in Android on EditText

When i am clicking on **Logout** button in my **Profile** Activity i want to take user to **Login** page, where he needs to use new credentials.

Hence i used this code:

    Intent intent = new Intent(ProfileActivity.this,
    		LoginActivity.class);
    intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); 
    intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    startActivity(intent);

in the `onButtonClick` of the Logout button.

But the problem is when i click device back button on the Login Activity it takes me to the ProfileActivity. I was expecting the application should close when i press device back button on LoginActivity.

What am i doing wrong?

I also added `android:launchMode=&quot;singleTop&quot;` in the manifest for my **LoginActivity**

Thank You

Android: Remove all the previous activities from the back stack

I have `adb` running and device is connected to my system in debugging mode,

I want to uninstall app using intent launch using `adb shell am start &lt;INTENT&gt;`

I don&#39;t want to uninstall using `adb uninstall com.company.apppackage` and I don&#39;t want to do it even by using `adb shell pm uninstall com.company.apppackage`

How can I send an intent with `android.intent.action.DELETE` action for a specific package allowing the user to see the prompt and uninstall the program?

adb shell command to make Android package uninstall dialog appear

I develop an app with a functionality for sharing text. This is working fine except for WhatsApp. What should I do? Is there any specific API for that?

How to share text to WhatsApp from my app?

I just started working with notifications and now I&#39;m trying to remove the notification and launch the app once the notification has been tapped in the notificationcenter.

I tried to work with the following code:

    import android.app.NotificationManager;
    
    public class ExpandNotification {
    	 private int NOTIFICATION = 546;
    	 private NotificationManager mNM;
    	 
    	 public void onCreate() {
            mNM.cancel(NOTIFICATION);
            setContentView(R.layout.activity_on);
            //Toast.makeText(this, &quot;stopped service&quot;, Toast.LENGTH_SHORT).show();
        }


I think this code executes the other class when tapped?

    PendingIntent contentIntent = PendingIntent.getActivity(this, REQUEST_CODE, new Intent(this, ExpandNotification.class), 0);

However the notification doesn&#39;t go away, nor does the application launch.
But I&#39;m able to swipe it to left or right to remove it but that&#39;s not what I want..

Removing notification after click

There seems to be an issue with my page here:
http://www.lonewulf.eu

When hovering over the thumbnails the image moves a bit on the right, and it only happens on Chrome.

My css:

    .img{
    	-ms-filter: &quot;progid:DXImageTransform.Microsoft.Alpha(Opacity=50)&quot;;
    	filter:alpha(opacity=50);
    	-moz-opacity: 0.5; 
    	opacity: 0.5;
    	-khtml-opacity: 0.5;
    	display:block;
    	border:1px solid #121212;
    }
    .img:hover{
    	-ms-filter: &quot;progid:DXImageTransform.Microsoft.Alpha(Opacity=100)&quot;;
    	filter:alpha(opacity=100);
    	-moz-opacity: 1; 
    	opacity: 1;
    	-khtml-opacity: 1;	
    	display:block;
    }

image moves on hover - chrome opacity issue

I think this problem is not Zope-related. Nonetheless I&#39;ll explain what I&#39;m trying to do:

I&#39;m using a PUT_factory in Zope to upload images to the ZODB per FTP. The uploaded image is saved as a Zope Image inside a newly created container object. This works fine, but I want to resize the image if it exceeds a certain size (width and height). So I&#39;m using the thumbnail function of PIL to resize them i.e. to 200x200. This works fine as long as the uploaded images are relatively small. I didn&#39;t check out the exact limit, but 976x1296px is still ok.

With bigger pictures I get: 

    Module PIL.Image, line 1559, in thumbnail
    Module PIL.ImageFile, line 201, in load
    IOError: image file is truncated (nn bytes not processed).

I tested a lot of jpegs from my camera. I don&#39;t think they are all truncated.

Here is my code:

    if img and img.meta_type == &#39;Image&#39;:
      pilImg = PIL.Image.open( StringIO(str(img.data)) )
    elif imgData:
      pilImg = PIL.Image.open( StringIO(imgData) )

    pilImg.thumbnail((width, height), PIL.Image.ANTIALIAS)

As I&#39;m using a PUT_factory, I don&#39;t have a file object, I&#39;m using either the raw data from the factory or a previously created (Zope) Image object.

I&#39;ve heard that PIL handles image data differently when a certain size is exceeded, but I don&#39;t know how to adjust my code. Or is it related to PIL&#39;s lazy loading?

PIL &quot;IOError: image file truncated&quot; with big images

I am working with images, and I ran into a problem with aspect ratios.

    &lt;img src=&quot;big_image.jpg&quot; width=&quot;900&quot; height=&quot;600&quot; alt=&quot;&quot; /&gt;

As you can see, `height` and `width` are already specified. I added a CSS rule for images:

    img {
      max-width: 500px;
    }

But for `big_image.jpg`, I receive `width=500` and `height=600`. How do I set images to be re-sized, whilst keeping their aspect ratios.

CSS force image resize and keep aspect ratio

I&#39;m looking to use an SVG logo for a website — to make it look great on a responsive design for all devices. 

But since [there are issues][1], I want to support as many devices and browsers as possible. Load speed is also an important consideration. How do export settings in Adobe Illustrator fit into all this?

In Illustrator, there are several options for SVG export. Firstly, **which SVG profile is best?**

![enter image description here][2]

I assume SVG Tiny has a lower file size? Do many devices support SVG Tiny? What are the most important differences? (Without having to read [this W3 monster][6].)

Secondly, I assume that the best option for image location is &quot;link&quot;? (See description after exclamation mark.)

![enter image description here][3]

Alternatively, how is browser support for the &quot;embed&quot; option?

![enter image description here][4]

Thank you!

&gt; P.S. There will be a fallback alpha-PNG option, but I want the SVG to
&gt; be supported as best as possible. (Come to think of it, a fallback
&gt; option — like a JPG — would probably be the best served in this case since alpha-PNG itself needs a solution for older IE.)

**Update:** There are also more options that can be configured. I am not working with text, so the only relevant one I see is the decimal places. For logos, something to be displayed as maximum 200x200px (so 400x400px on Retina displays), is &quot;3&quot; the best setting? Or &quot;2&quot; to minimize file size?

![enter image description here][5]




  [1]: http://caniuse.com/#search=svg
  [2]: http://i.stack.imgur.com/6DguE.png
  [3]: http://i.stack.imgur.com/rAHmN.png
  [4]: http://i.stack.imgur.com/3znoL.png
  [5]: http://i.stack.imgur.com/yvylr.png
  [6]: http://www.w3.org/TR/SVGMobile/

Optimal settings for exporting SVGs for the web from Illustrator?

I have an anchor that changes its background image when hovered with a class `class-btn` that contains a `background-image`. 

When hovered, it has 

    a.class-btn:hover
    {
        background-image(&#39;path/to/image-hovered.jpg&#39;);
    }

When the page loads the first time and you hover this button the first time, it blinks (it takes about half a second to download the hovered image). How to avoid that blinking without JavaScript (only simple css and html is allowed)?

I tried to search Stack Overflow for the similar question, but with no luck.

Just added:

* Should I &quot;preload&quot; the hovered image? How?
* Should I play with z-index or opacity? 

It happens with all browsers and thus the solution should work for all browsers.

css: avoid image hover first time blinking

As a general rule of thumb when is it appropriate to make a gif interlaced, a png interlaced and a jpeg progressive?

Especially when publishing the image on the web.

When to interlace an image?

So I have seen quite a few ways to darken images with CSS, including ones with rounded corners, but my problem is different.

Let&#39;s say I have an .png image that looks like a little dog (just go with it, I don&#39;t have any good examples), when I place it on my page, I give it dimensions of 100 x 100.

But I can&#39;t just overlay something on it, or tint the entire image, as it will cause the background of the dog to be tinted as well, which looks ugly.

Is it possible to tint an image of arbitrary shape with CSS?

(I&#39;m assuming you understand my point, and useless code is not necessary)

Thanks!

Darkening an image with CSS (In any shape)

I&#39;m having an issue with attempting to save some plots with transparent ellipsoids on them if I attempt to save them with .ps/.eps extensions. 

Here&#39;s the plot saved as a .png:
![png][1]

If I choose to save it as a .ps/.eps here is what it looks like:
![ps][2]

How I got around this, was to use ImageMagick to convert the original png to a ps. The only problem is that the image in png format is about 90k, and it becomes just under 4M after conversion. This is not good since I have a lot of these images, and it will take too much time to compile my latex document. Does anyone have a solution to this?

  [1]: http://i.stack.imgur.com/w55jg.png
  [2]: http://i.stack.imgur.com/loXbC.png

Matplotlib Plots Lose Transparency When Saving as .ps/.eps

I want to know about uses of png files. There are two formats available for *png images*; one is **png8** and the another one is **png24**. 

I would like to know that if I use either type in my `html` page, will there be any error? Or is this only quality matter?

What is difference between png8 and png24

I have about 200 grayscale PNG images stored within a directory like this.

    1.png
    2.png
    3.png
    ...
    ...
    200.png

I want to import all the PNG images as NumPy arrays.
How can I do this?

Importing PNG files into Numpy?

I am taking a jpg image and using numpy&#39;s fft2 to create/save a new image. However it throws this error 

    &quot;IOError: cannot write mode F as JPEG&quot; 

Is there an issue with CMYK and JPEG files in PIL???

    p = Image.open(&#39;kibera.jpg&#39;)
    bw_p = p.convert(&#39;L&#39;)
    array_p = numpy.asarray(bw_p)
    fft_p = abs(numpy.fft.rfft2(array_p))
    new_p = Image.fromarray(fft_p)
    new_p.save(&#39;kibera0.jpg&#39;)
    new_p.histogram()


PIL cannot write mode F to jpeg

I&#39;m using [`javax.imageio.ImageIO`][2] to save a `BufferedImage` as a jpeg file. 
In particular, I created the following Java function:

    public static void getScreenShot(BufferedImage capture, Path folder, String filename) {
            try {
                ImageIO.write(capture, &quot;jpeg&quot;, new File(folder.toString()+&quot;/&quot;+filename+&quot;.jpg&quot;));
            } catch (AWTException | IOException ex) {
                Logger.getLogger(ScreenShotMaker.class.getName()).log(Level.SEVERE, null, ex);
            }
    }

Likewise any image manipulation software, I wish to change the compression level of the jpeg file. However, I&#39;m searching for this option that seems to be missing in `ImageIO`. 

Can I set the compression level and how?


  [1]: http://docs.oracle.com/javase/6/docs/api/java/awt/Robot.html
  [2]: http://docs.oracle.com/javase/6/docs/api/javax/imageio/ImageIO.html

Setting jpg compression level with ImageIO in Java

I am trying to convert a Base64String to an image which needs to be saved locally.

At the moment, my code is able to save the image but when I open the saved image, it says &quot;Invalid Image&quot;.

![enter image description here][1]


  [1]: http://i.stack.imgur.com/s6aIa.png

Code:

    try
    {
        using (var imageFile = new StreamWriter(filePath))
        {
            imageFile.Write(resizeImage.Content);
            imageFile.Close();
        }
    }

The `Content` is a `string` object which contains the Base64 String.

C# Base64 String to JPEG Image

I am using Python (2.7) and bindings for OpenCV 2.4.6 on Ubuntu 12.04

I load an image

        image = cv2.imread(&#39;image.jpg&#39;)

I then check the shape of the image array

        print image.shape

I get (480, 640, 3), which I expect for a 640x480 colour image. I then convert the image to grayscale and check the shape again.

        gray_image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
        print gray_image.shape

I get (480, 640, 1), which I expect for a 640x480 **grayscale** image. I then save the image:

        cv2.imwrite(&#39;gray.jpg&#39;, gray_image)

I am on linux, so I tried looking at the image with gThumb, which shows all the colour channels. When I bring the gray image back into OpenCV the image has three channels again.
I am aware of this flag for reading images:

        CV_LOAD_IMAGE_GRAYSCALE - If set, always convert image to the grayscale one

But this sounds like it is going to bring in the image as a colour image and then convert it. I am porting this project to RaspberryPi so I don&#39;t want unecessary operatioms happening.

EDIT: I have done some timing checks and I have discovered that loading an image using the CV_LOAD_IMAGE_GRAYSCALE flag set results in the image loading twice as fast, irrespective of the image input.

         Using a 3072 x 4608 x 3 image
         0.196774959564 seconds with default loading
         0.0931899547577 seconds with CV_LOAD_IMAGE_GRAYSCALE

**The problem seems to be that OpenCV is creating a 3 channel JPG output whether I have a grayscale image matrix or not!**

What other app can I use to make sure I am getting a single 8 bit channel JPG image out??
(Perhaps gThumb is reporting the channels incorrectly).

If the image is not single channel, why is OpenCV saving my grayscale image to a 3 channel image at disk write?

Thanks in advance.


Content Type	Original Author	Original Content on Stackoverflow
Question	Victor Santiago	View Question on Stackoverflow
Solution 1 - Android	Parag Meshram	View Answer on Stackoverflow
Solution 2 - Android	Hayk Saakian	View Answer on Stackoverflow

Why should I use PNG and not JPG?

Android Problem Overview

Android Solutions

Solution 1 - Android

Solution 2 - Android

Using pointers to remove item from singly-linked list

Errno 10061 : No connection could be made because the target machine actively refused it ( client - server )

Attributions