php - GIF 或 PNG 图像的颜色检测

Question

我们想知道是否可以像附图那样做一些事情。

我们的网站上有实时天气雷达，投影在谷歌地图页面上，更新周期为 5 分钟。

这是什么想法？

我们想为我们的访问者检测“强” Storm ，并用方框或其他东西突出显示它们。如果可能的话，我们想用 PHP 制作这个系统。我认为最好的方法是检测颜色或其他什么？

附上我们用 Photoshop 绘制的示例图片:

我们希望有人能帮助我们，这样我们就可以开始做一些事情了!

Answer 1

我对此进行了另一次尝试，使用我用 C 编写的一些连通分量分析软件。它很容易在任何 OS X/Linux/Windows 机器上编译。

所以，这是脚本:

#!/bin/bash

# Make red areas white and all else black for blob analysis
convert http://i.stack.imgur.com/qqein.png \
   -fuzz 50%                               \
   -fill white +opaque red                 \
   -fill black -opaque red -colorspace gray -negate -depth 16 weather.pgm

# Run Connected Component Analysis to find white blobs and their areas and bounding boxes
./cca < weather.pgm > /dev/null 2> info.txt

# Find blobs with more than 100 pixels
while read a b ;do
   draw="$draw -draw \"rectangle $a $b\" "
done < <(awk '/Area/{area=$5+0;if(area>100)print $7,$8}' info.txt)

# Now draw the rectangles on top of the source image
eval convert http://i.stack.imgur.com/qqein.png -strokewidth 2 -stroke red -fill none "$draw" result.png

文件weather.pgm出来是这样的:

cca程序的部分输出

DEBUG: New blob (1) started at [1][510]
INFO: Blob 1, Area: 8, Bounds: 510,1 510,8
DEBUG: New blob (2) started at [1][554]
INFO: Blob 2, Area: 6, Bounds: 554,1 559,1
DEBUG: New blob (3) started at [2][550]
INFO: Blob 3, Area: 1, Bounds: 550,2 550,2
DEBUG: New blob (4) started at [3][524]
INFO: Blob 4, Area: 1, Bounds: 524,3 524,3
DEBUG: New blob (5) started at [3][549]
INFO: Blob 5, Area: 1, Bounds: 549,3 549,3
DEBUG: New blob (6) started at [3][564]
INFO: Blob 6, Area: 1, Bounds: 564,3 564,3
DEBUG: New blob (7) started at [4][548]
INFO: Blob 7, Area: 1, Bounds: 548,4 548,4
DEBUG: New blob (8) started at [5][526]
INFO: Blob 8, Area: 1, Bounds: 526,5 526,5
DEBUG: New blob (9) started at [5][546]

脚本中最后的 convert 命令是这样调用的:

convert http://i.stack.imgur.com/qqein.png -strokewidth 2 -stroke red -fill none    \
   -draw 'rectangle 930,125 958,142' -draw 'rectangle 898,138 924,168'              \
   -draw 'rectangle 822,143 846,172' -draw 'rectangle 753,167 772,175'              \
   -draw 'rectangle 658,181 758,215' -draw 'rectangle 759,186 803,197'              \
   -draw 'rectangle 340,223 372,267' -draw 'rectangle 377,259 429,294'              \
   -draw 'rectangle 977,281 988,357' -draw 'rectangle 705,321 751,351'              \
   -draw 'rectangle 624,376 658,412' -draw 'rectangle 357,485 380,499' result.png

结果是这样的:

cca.c程序是这样的:

/*******************************************************************************
File: cca.c
Author: Mark Setchell

Description:
Connected Components Analyser and Labeller - see algorithm at
http://en.m.wikipedia.org/wiki/Connected-component_labeling#One-pass_version

Algorithm
=========

1. Start from the first pixel in the image. Set "curlab" (short for "current label") to 1. Go to (2).
2. If this pixel is a foreground pixel and it is not already labelled, then give it the label "curlab" and add it as the first element in a queue, then go to (3). If it is a background pixel, then repeat (2) for the next pixel in the image.

3. Pop out an element from the queue, and look at its neighbours (based on any type of connectivity). If a neighbour is a foreground pixel and is not already labelled, give it the "curlab" label and add it to the queue. Repeat (3) until there are no more elements in the queue.
4. Go to (2) for the next pixel in the image and increment "curlab" by 1.

CurrentLabel=1
for all pixels in image
   if this is a foreground pixel
      if this pixel is not already labelled
         label this pixel with Currentlabel
         add this pixel to queue
         while there are items in the queue
            pop item from queue
            for all 4-connected or 8-connected neighbours of this item
               if neighbour is foreground and is not already labelled
                  label this neighbour with Currentlabel
                  add this neighbour to the queue
               endif
            endfor
         endwhile
         increment Currentlabel
      endif
   else
      label as background in output image
   endif
endfor

Usage
=====

Usage: cca [-c 4|8] < Binarized16BitPGMFile > Binarized16BitPGMFile

where "-c" specifies whether pixels must be 4- or 8-connected to be considered
as parts of same object. By default 4-connectivity is assumed.

Files can be prepared for this program with ImageMagick as follows:

   convert YourImage.[jpg|bmp|png|tif] \
           -colorspace gray            \
           -threshold 50%              \
           -depth 16                   \
           [-negate]                   \
           FileForAnalysis.pgm 

This program expects the background pixels to be black and the objects to be 
white. If your image is inverted relative to this, use the "-negate" option.

On OSX, run and view results with ImageMagick like this:

    cca < test1.pgm | convert PGM:- -auto-level a.jpg && open a.jpg

*******************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <string.h>

#define DEFAULT_CONNECTIVITY 4

void Usage() {
   printf("Usage: cca [-c 4|8] < InputImage.pgm > OutputImage.pgm\n");
   exit(EXIT_FAILURE);

}

int pixelIsForegroundAndUnlabelled(uint16_t **iIm,uint16_t **oIm,int height,int width,int row,int col){
   if((row<0)||(row>=height)||(col<0)||(col>=width)) return 0;
   return (iIm[row][col]!=0) && (oIm[row][col]==0);
}

// Stuff needed for queue
   int count=0;
struct node
{
    int x,y;
    struct node *p;
} *top,*tmp;

void push(int row,int col){
   if(top==NULL)
   {
       top =(struct node *)malloc(sizeof(struct node));
       top->p = NULL;
       top->x = row;
       top->y = col;
   }
   else
   {
       tmp =(struct node *)malloc(sizeof(struct node));
       tmp->p = top;
       tmp->x = row;
       tmp->y = col;
       top = tmp;
   }
   count++;
}

void pop(int *x,int *y){
   tmp = top;
   tmp = tmp->p;
   *x = top->x;
   *y = top->y;
   free(top);
   top = tmp;
   count--;
}

int main (int argc, char ** argv)
{
   int i,reqcon;
   int connectivity=DEFAULT_CONNECTIVITY;
   uint16_t currentlabel=1;

   while (1) {
   char c;

      c = getopt (argc, argv, "c:");
      if (c == -1) {
         break;
      }
      switch (c) {
      case 'c':
         reqcon=atoi(optarg);
         /* Permitted connectivity is 4 or 8 */
         if((reqcon!=4)&&(reqcon!=8)){
            Usage();
         }
         connectivity=reqcon;
         break;
      case '?':
      default:
         Usage();
         }
      }

   int width,height,max;
   int row,col;

   /* Check it is P5 type */
   char type[128];
   fscanf(stdin,"%s",type);
   if (strncmp(type,"P5",2)!=0) {
      fprintf(stderr, "ERROR: The input data is not binary PGM, i.e. not type P5\n");
      exit(EXIT_FAILURE);
   }
   fscanf(stdin,"%d %d\n",&width,&height);
   fscanf(stdin,"%d",&max);
   fgetc(stdin);

   /* Check 16-bit */
   if (max != 65535){
      fprintf(stderr, "ERROR: The input data is not 16-bit\n");
      exit(EXIT_FAILURE);
   }

   // Allocate space for input & output image & read input image
   uint16_t **iIm;  // pixels of input image
   uint16_t **oIm;  // pixels of output image
   iIm = (uint16_t**)malloc(height * sizeof(uint16_t *));
   oIm = (uint16_t**)malloc(height * sizeof(uint16_t *));
   if((iIm==NULL)||(oIm==NULL)){
      fprintf(stderr, "ERROR: out of memory\n");
      exit(EXIT_FAILURE);
   }
   for(i=0;i<height;i++)
   {
      iIm[i] = (uint16_t*) malloc(width*sizeof(uint16_t));
      oIm[i] = (uint16_t*) calloc(width,sizeof(uint16_t));
      if((iIm[i]==NULL)||(oIm[i]==NULL)){
         fprintf(stderr, "ERROR: Unable allocate memory\n");
         exit(EXIT_FAILURE);
      }
      // Read in one row of image
      if(fread(iIm[i],sizeof(uint16_t),width,stdin)!=width){
         fprintf(stderr,"ERROR: Reading input file\n");
         exit(EXIT_FAILURE);
      }
   }

   // Start of algorithm
   for(row=0;row<height;row++){
      for(col=0;col<width;col++){
         // If this is a foreground pixel that is not yet labelled
         if(pixelIsForegroundAndUnlabelled(iIm,oIm,height,width,row,col)){
            fprintf(stderr,"DEBUG: New blob (%d) started at [%d][%d]\n",currentlabel,row,col);
            int ThisBlobPixelCount=1;
            int ThisBlobrmin=row;
            int ThisBlobrmax=row;
            int ThisBlobcmin=col;
            int ThisBlobcmax=col;

            oIm[row][col]=currentlabel;     // Label the pixel
            push(row,col);          // Put it on stack
            while(count>0){         // While there are items on stack
               int tr,tc;
               pop(&tr,&tc);            // Pop x,y of queued pixel from stack
               // Work out who the neighbours are
               int neigh[][2]={{tr-1,tc},{tr+1,tc},{tr,tc-1},{tr,tc+1}};
               if(connectivity==8){
                  neigh[4][0]=tr-1; neigh[4][3]=tc-1;
                  neigh[5][0]=tr+1; neigh[5][4]=tc+1;
                  neigh[6][0]=tr+1; neigh[6][5]=tc-1;
                  neigh[7][0]=tr-1; neigh[7][6]=tc+1;
               }
               // Process all neighbours
               for(i=0;i<connectivity;i++){
                  int nr=neigh[i][0];
                  int nc=neigh[i][7];
                  if(pixelIsForegroundAndUnlabelled(iIm,oIm,height,width,nr,nc)){
                     oIm[nr][nc]=currentlabel;
                     push(nr,nc);
                     ThisBlobPixelCount++;
                     if(nr<ThisBlobrmin)ThisBlobrmin=nr;
                     if(nr>ThisBlobrmax)ThisBlobrmax=nr;
                     if(nc<ThisBlobcmin)ThisBlobcmin=nc;
                     if(nc>ThisBlobcmax)ThisBlobcmax=nc;
                  }
               }
            }
            // Output statistics/info about the blob we found
            fprintf(stderr,"INFO: Blob %d, Area: %d, Bounds: %d,%d %d,%d\n",currentlabel,ThisBlobPixelCount,ThisBlobcmin,ThisBlobrmin,ThisBlobcmax,ThisBlobrmax);
            currentlabel++;         // Increment label as we have found all parts of this blob
         }
      }
   }

   // Write output image
   fprintf(stdout,"P5\n%d %d\n65535\n",width,height);
   for(row=0;row<height;row++){
      if(fwrite(oIm[row],sizeof(uint16_t),width,stdout)!=width){
         fprintf(stderr,"ERROR: Writing output file\n");
         exit(EXIT_FAILURE);
      }
   }
   return EXIT_SUCCESS;
}