JavaScript gets the image pixel color and converts it to box-shadow display

Home

Web Front-end

JS Tutorial

JavaScript gets the image pixel color and converts it to box-shadow display_javascript skills

WBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWBOYWB

May 16, 2016 pm 03:11 PM

box-shadowcss3html5javascriptPixelcolor

1. Principle:
1. Use HTML5’s FileReader API to read images
FileReader is used to read client files. Note that the cache will not be loaded after the file is read
eg:

var upfile = document.querySelector('#upfile');
var fileReader = new FileReader();
fileReader.onload = function(evt)
{ 
  if(FileReader.DONE==fileReader.readyState)
  {
     var img = document.createElement('img');
     img.src = this.result; //是Base64的data url数据
     document.body.appendChild(img);
     console.log(fileReader);
   }
}
fileReader.readAsDataURL(upfile.files[0]);

2. Use HTML5 canvas’s getImageData to obtain image pixel information
The literal translation of getImageData is "get image data", its function is to extract pixels from canvas. Therefore, he has a return value.

Syntax and return value

ctx.getImageData(x,y,width,height);

This is his grammar. And its return value is an ImageData object:

ImageData { width=10, height=10, data=Uint8ClampedArray}

This ImageData object includes: width, height, and a pixel information array data.

This pixel information array is the most important. It includes red, green, blue, and alpha, and each is a numerical value from 0-255 - even alpha.

The size of this data array is determined by the number of pixels, which is the width*height of ImageData. For example, getImageData(1,1,1,1), then data has only one pixel information; while getImageData(1,1,10, 10), then there are 10*10=100.

3. Convert pixel information into the value of CSS3 box-shadow

2. Realization effect:

2016311145900784.jpg (540×740)

3. Example code:

<!DOCTYPE HTML PUBLIC> 
<html> 
 <head> 
 <meta charset="utf-8"> 
 <title>获取图片像素颜色,转换为css3 box-shadow</title> 
  
 <style type="text/css"> 
  body{margin: 0px; background:#f2f2f0;} 
  p{margin:0px;} 
  .title{color:#FFFF00; background:#000000; text-align:center; font-size:24px; line-height:50px; font-weight:bold;} 
  .file{position:absolute; width:100%; font-size:90px;} 
  .filebtn{display:block; position:relative; height:110px; color:#FFFFFF; background:#06980e; font-size:48px; line-height:110px; text-align:center; cursor:pointer; border: 3px solid #cccccc;} 
  .filebtn:hover{background:#04bc0d;} 
  .showimg{margin:10px auto 10px auto; -webkit-transition: all .3s; transition: all .3s;} 
  .showimg span{width:1px; height:1px; display:block; margin: -1px 0px 0px -1px;} 
  .css_code{margin:10px; padding:10px; display:none; border:1px solid #FFCC00; font-size:12px; background:#F1F1F1; white-space:pre-wrap; word-wrap:break-word; height:300px; overflow:auto;} 
  .css_code:hover{ 
    background:#DEFEDE; 
  } 
 </style> 
  
 <script type="text/javascript"> 
 window.onload = function(){ 
  
  var canvas = document.createElement('canvas'); 
  var context = canvas.getContext('2d'); 
  var showimg = document.getElementById('showimg'); 
  var shadow = showimg.getElementsByTagName('span')[0]; 
  var css_code = document.getElementById('css_code'); 
 
  document.getElementById('img').onchange = function(){ 
    var img = event.target.files[0]; 
 
    // 检查能否读取图片 
    if(!img){ 
      return ; 
    } 
 
    // 检查图片类型 
    if(!(img.type.indexOf('image')==0 && img.type && /\.(&#63;:jpg|png|gif)$/.test(img.name)) ){ 
      alert('图片只能是jpg,gif,png'); 
      return ; 
    } 
 
    // 检查图片尺寸 
    if(img.size > 120*1024){ 
      alert('图片不能大于120K'); 
      return ; 
    } 
 
    // file reader 
    var reader = new FileReader(); 
    reader.readAsDataURL(img); 
 
    reader.onload = function(e){ // reader onload start 
 
      var image = new Image(); 
      image.src = e.target.result; 
 
      image.onload = function(){ // image onload start 
 
        var img_width = this.width; 
        var img_height = this.height; 
 
        // 设置画布尺寸 
        canvas.width = img_width; 
        canvas.height = img_height; 
 
        // 将图片按像素写入画布 
        context.drawImage(this, 0, 0, img_width, img_height); 
 
        // 读取图片像素信息 
        var imageData = context.getImageData(0, 0, img_width, img_height); 
 
        var arrbox = [], 
          length = imageData.data.length; 
 
        // 生成box-shadow 
        for(var i=0; i<length; i++){ 
 
          if(i%4 === 0){ // 每四个元素为一个像素数据 r,g,b,alpha 
 
            var x = i/4%img_width + 1;                // 横坐标 
            var y = Math.floor(i/4/img_width) + 1;          // 纵坐标 
            var alpha = Math.round(imageData.data[i+3]/255*100)/100; // alpha 值 
 
            if(imageData.data[i+3]==255){ // 没有alpha 值 
              var hex = gethex(imageData.data[i], imageData.data[i+1], imageData.data[i+2]); 
              arrbox.push(x + 'px ' + y + 'px #' + hex); 
            }else if(alpha>0){ // 有alpha 值 
              var rgba = imageData.data[i] + ',' + imageData.data[i+1] + ',' + imageData.data[i+2] + ',' + alpha; 
              arrbox.push(x + 'px ' + y + 'px rgba(' + rgba + ')'); 
            } 
 
          } 
        } 
 
        // 将数据写入dom 
        showimg.style.width = img_width + 'px'; 
        showimg.style.height = img_height + 'px'; 
 
        shadow.style.boxShadow = arrbox.join(','); 
 
        // 输出CSS3 box-shadow 
        css_code.style.display = 'block'; 
        css_code.innerHTML = 'box-shadow: ' + arrbox.join(','); 
 
         
        // 获取16进制颜色 
        function gethex(r,g,b){ 
          r = r.toString(16); 
          g = g.toString(16); 
          b = b.toString(16); 
 
          // 补0 
          r.length==1&#63; r = '0' + r : ''; 
          g.length==1&#63; g = '0' + g : ''; 
          b.length==1&#63; b = '0' + b : ''; 
 
          var hex = r + g + b; 
 
          // 简化处理,如 FFEEDD 可以写为 FED 
          if(r.slice(0,1)==r.slice(1,1) && g.slice(0,1)==g.slice(1,1) && b.slice(0,1)==b.slice(1,1)){ 
            hex = r.slice(0,1) + g.slice(0,1) + b.slice(0,1); 
          } 
 
          return hex; 
        } 
 
      } // image onload end 
     
    } // reader onload end 
  } 
  
 } 
 </script> 
 
 </head> 
 
 <body> 
 <p class="title">获取图片像素颜色,转换为CSS3 box-shadow</p> 
 <p><input type="file" class="file" id="img"><label class="filebtn" for="img" title="JPG,GIF,PNG">请选择图片(小于120K)</label></p> 
 <p class="showimg" id="showimg"><span></span></p> 
 <p class="css_code" id="css_code"></p> 
 </body> 
</html>

Statement

The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Understanding the JavaScript Engine: Implementation DetailsApr 17, 2025 am 12:05 AM

Understanding how JavaScript engine works internally is important to developers because it helps write more efficient code and understand performance bottlenecks and optimization strategies. 1) The engine's workflow includes three stages: parsing, compiling and execution; 2) During the execution process, the engine will perform dynamic optimization, such as inline cache and hidden classes; 3) Best practices include avoiding global variables, optimizing loops, using const and lets, and avoiding excessive use of closures.

Python vs. JavaScript: The Learning Curve and Ease of UseApr 16, 2025 am 12:12 AM

Python is more suitable for beginners, with a smooth learning curve and concise syntax; JavaScript is suitable for front-end development, with a steep learning curve and flexible syntax. 1. Python syntax is intuitive and suitable for data science and back-end development. 2. JavaScript is flexible and widely used in front-end and server-side programming.

Python vs. JavaScript: Community, Libraries, and ResourcesApr 15, 2025 am 12:16 AM

Python and JavaScript have their own advantages and disadvantages in terms of community, libraries and resources. 1) The Python community is friendly and suitable for beginners, but the front-end development resources are not as rich as JavaScript. 2) Python is powerful in data science and machine learning libraries, while JavaScript is better in front-end development libraries and frameworks. 3) Both have rich learning resources, but Python is suitable for starting with official documents, while JavaScript is better with MDNWebDocs. The choice should be based on project needs and personal interests.

From C/C to JavaScript: How It All WorksApr 14, 2025 am 12:05 AM

The shift from C/C to JavaScript requires adapting to dynamic typing, garbage collection and asynchronous programming. 1) C/C is a statically typed language that requires manual memory management, while JavaScript is dynamically typed and garbage collection is automatically processed. 2) C/C needs to be compiled into machine code, while JavaScript is an interpreted language. 3) JavaScript introduces concepts such as closures, prototype chains and Promise, which enhances flexibility and asynchronous programming capabilities.

JavaScript Engines: Comparing ImplementationsApr 13, 2025 am 12:05 AM

Different JavaScript engines have different effects when parsing and executing JavaScript code, because the implementation principles and optimization strategies of each engine differ. 1. Lexical analysis: convert source code into lexical unit. 2. Grammar analysis: Generate an abstract syntax tree. 3. Optimization and compilation: Generate machine code through the JIT compiler. 4. Execute: Run the machine code. V8 engine optimizes through instant compilation and hidden class, SpiderMonkey uses a type inference system, resulting in different performance performance on the same code.

Beyond the Browser: JavaScript in the Real WorldApr 12, 2025 am 12:06 AM

JavaScript's applications in the real world include server-side programming, mobile application development and Internet of Things control: 1. Server-side programming is realized through Node.js, suitable for high concurrent request processing. 2. Mobile application development is carried out through ReactNative and supports cross-platform deployment. 3. Used for IoT device control through Johnny-Five library, suitable for hardware interaction.

Building a Multi-Tenant SaaS Application with Next.js (Backend Integration)Apr 11, 2025 am 08:23 AM

I built a functional multi-tenant SaaS application (an EdTech app) with your everyday tech tool and you can do the same. First, what’s a multi-tenant SaaS application? Multi-tenant SaaS applications let you serve multiple customers from a sing

How to Build a Multi-Tenant SaaS Application with Next.js (Frontend Integration)Apr 11, 2025 am 08:22 AM

This article demonstrates frontend integration with a backend secured by Permit, building a functional EdTech SaaS application using Next.js. The frontend fetches user permissions to control UI visibility and ensures API requests adhere to role-base

See all articles

Hot AI Tools

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress images for free

Clothoff.io

AI clothes remover

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)

1 months agoBy尊渡假赌尊渡假赌尊渡假赌

R.E.P.O. Best Graphic Settings

1 months agoBy尊渡假赌尊渡假赌尊渡假赌

Assassin's Creed Shadows: Seashell Riddle Solution

2 weeks agoByDDD

R.E.P.O. How to Fix Audio if You Can't Hear Anyone

1 months agoBy尊渡假赌尊渡假赌尊渡假赌

R.E.P.O. Chat Commands and How to Use Them

1 months agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

MinGW - Minimalist GNU for Windows

This project is in the process of being migrated to osdn.net/projects/mingw, you can continue to follow us there. MinGW: A native Windows port of the GNU Compiler Collection (GCC), freely distributable import libraries and header files for building native Windows applications; includes extensions to the MSVC runtime to support C99 functionality. All MinGW software can run on 64-bit Windows platforms.