Asked  7 Months ago    Answers:  5   Viewed   24 times

I have a jpg image.

I need to know "overall average" the color of the image. At first glance there can use the histogram of the image (channel RGB).

At work I use mostly JavaScript and PHP (a little Python) therefore welcomed the decision in these languages. Maybe ther are library for working with images that address similar problems.

I do not need to dynamically determine the color of the picture. I need just once go through the entire array of images and determine the color of each separately (this information I will remember for future use).



You can use PHP to get an array of the color palette like so:

function colorPalette($imageFile, $numColors, $granularity = 5) 
   $granularity = max(1, abs((int)$granularity)); 
   $colors = array(); 
   $size = @getimagesize($imageFile); 
   if($size === false) 
      user_error("Unable to get image size data"); 
      return false; 
   $img = @imagecreatefromjpeg($imageFile);
   // Andres mentioned in the comments the above line only loads jpegs, 
   // and suggests that to load any file type you can use this:
   // $img = @imagecreatefromstring(file_get_contents($imageFile)); 

      user_error("Unable to open image file"); 
      return false; 
   for($x = 0; $x < $size[0]; $x += $granularity) 
      for($y = 0; $y < $size[1]; $y += $granularity) 
         $thisColor = imagecolorat($img, $x, $y); 
         $rgb = imagecolorsforindex($img, $thisColor); 
         $red = round(round(($rgb['red'] / 0x33)) * 0x33); 
         $green = round(round(($rgb['green'] / 0x33)) * 0x33); 
         $blue = round(round(($rgb['blue'] / 0x33)) * 0x33); 
         $thisRGB = sprintf('%02X%02X%02X', $red, $green, $blue); 
         if(array_key_exists($thisRGB, $colors)) 
            $colors[$thisRGB] = 1; 
   return array_slice(array_keys($colors), 0, $numColors); 
// sample usage: 
$palette = colorPalette('rmnp8.jpg', 10, 4); 
echo "<table>n"; 
foreach($palette as $color) 
   echo "<tr><td style='background-color:#$color;width:2em;'>&nbsp;</td><td>#$color</td></tr>n"; 
echo "</table>n";

Which gives you an array whose values are higher for how often that color has been used.

EDIT A commenter asked how to use this on all files in a directory, here it is:

    if ($handle = opendir('./path/to/images')) {

        while (false !== ($file = readdir($handle))) {
           $palette = colorPalette($file, 10, 4);
           echo "<table>n"; 
           foreach($palette as $color) { 
               echo "<tr><td style='background-color:#$color;width:2em;'>&nbsp;</td><td>#$color</td></tr>n"; 
           echo "</table>n";

might not want to do this on too many files, but it's your server.

Alternatively if you'd rather use Javascript Lokesh's Color-Theif library does exactly what you're looking for.

Wednesday, March 31, 2021
answered 7 Months ago

You can try loading the image with the Python Image Lirbary (PIL) and then save it again to a different file. That should remove the meta data.

Sunday, June 13, 2021
answered 5 Months ago

You can do this using attributes. First define your attribute in attrs.xml (this file goes under the 'values' folder):

<?xml version="1.0" encoding="utf-8"?>
    <attr name="myCoolColor" format="color" />

Then in your styles.xml, define myCoolColor for each theme:

<style name="Theme.MyApp" parent="@style/Theme.Light">
   <item name="myCoolColor">#123456</item>

<style name="Theme.MyApp.Dark" parent="@style/Theme.Dark">
   <item name="myCoolColor">#654321</item>

Now, specify myCoolColor as the background of your view:


You can go further and use a reference to a color so you can keep your colors defined in one place. Change the attribute to include a reference (note that we can use a color OR a reference):

<?xml version="1.0" encoding="utf-8"?>
    <attr name="myCoolColor" format="color|reference" />

Change your styles.xml to reference a color for each theme:

<style name="Theme.MyApp" parent="@style/Theme.Light">
   <item name="myCoolColor">@color/blue</item>

<style name="Theme.MyApp.Dark" parent="@style/Theme.Dark">
   <item name="myCoolColor">@color/green</item>

Finally define the colors in your colors.xml:

<?xml version="1.0" encoding="utf-8"?>
    <color name="blue">#0000FF</color>
    <color name="green">#00FF00</color>

That's it!

Wednesday, July 28, 2021
answered 3 Months ago

What matlab edge() do should be

  1. Compute LoG
  2. Compute zero crossings on LoG
  3. Compute a threshold for local LoG difference
  4. Edge pixels = zero crossing && local difference > threshold

The LoG filter of scipy only does step 1 above. I implemented the following snippet to mimic step 2~4 above:

import scipy as sp
import numpy as np
import scipy.ndimage as nd
import matplotlib.pyplot as plt
from skimage import data    

# lena = sp.misc.lena() this function was deprecated in version 0.17
img =  # use a standard image from skimage instead
LoG = nd.gaussian_laplace(img , 2)
thres = np.absolute(LoG).mean() * 0.75
output = sp.zeros(LoG.shape)
w = output.shape[1]
h = output.shape[0]

for y in range(1, h - 1):
    for x in range(1, w - 1):
        patch = LoG[y-1:y+2, x-1:x+2]
        p = LoG[y, x]
        maxP = patch.max()
        minP = patch.min()
        if (p > 0):
            zeroCross = True if minP < 0 else False
            zeroCross = True if maxP > 0 else False
        if ((maxP - minP) > thres) and zeroCross:
            output[y, x] = 1


This of course is slow and probably not idiomatic as I am also new to Python, but should show the idea. Any suggestion on how to improve it is also welcomed.

Thursday, August 12, 2021
Miguel Ping
answered 3 Months ago

You'll need to use the Accelerate Library, Apple has a manual with some sample code, it'll work in Swift or ObjC

Here is a sample to get you going, I use this to calculate a person's heart rate and heart rate variability using the change in colors of a finger over the camera lens.

Full code here:

It's in an older version of Swift but I think you'll get the idea. I was doing this at 240 fps, but with a cropped smaller section of the image.

Relevant code here:

// compute the brightness for reg, green, blue and total
    // pull out color values from pixels ---  image is BGRA
    var greenVector:[Float] = Array(count: numberOfPixels, repeatedValue: 0.0)
    var blueVector:[Float] = Array(count: numberOfPixels, repeatedValue: 0.0)
    var redVector:[Float] = Array(count: numberOfPixels, repeatedValue: 0.0)

    vDSP_vfltu8(dataBuffer, 4, &blueVector, 1, vDSP_Length(numberOfPixels))
    vDSP_vfltu8(dataBuffer+1, 4, &greenVector, 1, vDSP_Length(numberOfPixels))
    vDSP_vfltu8(dataBuffer+2, 4, &redVector, 1, vDSP_Length(numberOfPixels))

    // compute average per color
    var redAverage:Float = 0.0
    var blueAverage:Float = 0.0
    var greenAverage:Float = 0.0

    vDSP_meamgv(&redVector, 1, &redAverage, vDSP_Length(numberOfPixels))
    vDSP_meamgv(&greenVector, 1, &greenAverage, vDSP_Length(numberOfPixels))
    vDSP_meamgv(&blueVector, 1, &blueAverage, vDSP_Length(numberOfPixels))

    // convert to HSV ( hue, saturation, value )
    // this gives faster, more accurate answer
    var hue: CGFloat = 0.0
    var saturation: CGFloat = 0.0
    var brightness: CGFloat = 0.0
    var alpha: CGFloat = 1.0

    var color: UIColor = UIColor(red: CGFloat(redAverage/255.0), green: CGFloat(greenAverage/255.0), blue: CGFloat(blueAverage/255.0), alpha: alpha)
    color.getHue(&hue, saturation: &saturation, brightness: &brightness, alpha: &alpha)

    // 5 count rolling average
    let currentHueAverage = hue/movingAverageCount

    let movingAverage = movingAverageArray[0] + movingAverageArray[1] + movingAverageArray[2] + movingAverageArray[3] + movingAverageArray[4]
Sunday, September 5, 2021
Shimmy Weitzhandler
answered 2 Months ago
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