如何使用Android NDK将头像变成“遗像”

看完本文的标题,可能有人要打我。你说黑白的老照片不好吗?非要说什么遗像,我现在就把你变成遗像!好了,言归正传。我想大部分人都用过美颜相机或者剪映等软件吧,它们的滤镜功能是如何实现的,有人想过吗?难道要使用Java/Kotlin遍历Bitmap,然后处理到手机发烫吗?学过计算机图形学的应该知道,图片或视频的图像数据的最小单位是像素px。视频编码H.264的YUV数据不也是视频像素数据嘛,只不过有很多帧。

代码实现

本篇文章,我来教大家简单的处理图像中一个个的像素点的色值,从而达到改变图片风格的效果。首先我们创建一个Native C++项目。

然后我们需要写个简单的xml布局。

xml 复制代码
<?xml version="1.0" encoding="utf-8"?>

<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <ImageView
        android:id="@+id/iv_display"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
    <Button
        android:id="@+id/btnPicProcess"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        android:text="黑白"/>

</androidx.constraintlayout.widget.ConstraintLayout>

接下来我们需要实现Activity的代码了。注意这里有个external方法,它相当于java中的带native关键字的方法,只不过这是kotlin的写法。在handleBitmap()方法中调用底层方法处理图像。就这么一个简单的流程,因为我们把图像处理的逻辑全部都放到c++底层代码中了。之所以把图像处理的逻辑全权交给C++的原因我想大家应该都知道了,IO是非常耗时的,而两层循环的时间复杂度是O(n²)。那就是java使用jni跟c++频繁通信会大量调输入输出流,时间都损耗在bitmap的setPixels方法上了。那还不如你处理好了给我结果就好了,我不需要关心过程。

kotlin 复制代码
package com.dorachat.myapplication

import android.graphics.Bitmap
import android.graphics.BitmapFactory
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import com.dorachat.myapplication.databinding.ActivityMainBinding

class MainActivity : AppCompatActivity() {

    private lateinit var binding: ActivityMainBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        val bitmap = BitmapFactory.decodeResource(resources, R.drawable.pic)
        binding.ivDisplay.setImageBitmap(bitmap)
        binding.btnPicProcess.setOnClickListener {
            binding.ivDisplay.setImageBitmap(handleBitmap(bitmap))
        }
    }
    
    /**
     * jni处理图片。
     */
    private fun handleBitmap(bitmap: Bitmap) : Bitmap {
        val bmp = bitmap.copy(Bitmap.Config.ARGB_8888, true);
        nativeProcessBitmap(bmp);
        return bmp;
    }

    /**
     * 黑白特效,调用native底层方法。
     */
    external fun nativeProcessBitmap(bitmap: Bitmap)

    companion object {
        // Used to load the 'myapplication' library on application startup.
        init {
            System.loadLibrary("myapplication")
        }
    }
}

我们再来看下CMakeLists.txt的代码,注意target_link_libraries中要链接jnigraphics。

cmake 复制代码
# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html.
# For more examples on how to use CMake, see https://github.com/android/ndk-samples.

# Sets the minimum CMake version required for this project.
cmake_minimum_required(VERSION 3.22.1)

# Declares the project name. The project name can be accessed via ${ PROJECT_NAME},
# Since this is the top level CMakeLists.txt, the project name is also accessible
# with ${CMAKE_PROJECT_NAME} (both CMake variables are in-sync within the top level
# build script scope).
project("myapplication")

# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.
#
# In this top level CMakeLists.txt, ${CMAKE_PROJECT_NAME} is used to define
# the target library name; in the sub-module's CMakeLists.txt, ${PROJECT_NAME}
# is preferred for the same purpose.
#
# In order to load a library into your app from Java/Kotlin, you must call
# System.loadLibrary() and pass the name of the library defined here;
# for GameActivity/NativeActivity derived applications, the same library name must be
# used in the AndroidManifest.xml file.
add_library(${CMAKE_PROJECT_NAME} SHARED
        # List C/C++ source files with relative paths to this CMakeLists.txt.
        native-lib.cpp)

# Specifies libraries CMake should link to your target library. You
# can link libraries from various origins, such as libraries defined in this
# build script, prebuilt third-party libraries, or Android system libraries.
target_link_libraries(${CMAKE_PROJECT_NAME}
        # List libraries link to the target library
        android
        log
        jnigraphics)

最后就是我们最最重要的底层代码了。通过调用AndroidBitmap_getInfo来读取图片像素数据,并将其保存在AndroidBitmapInfo中。AndroidBitmap_lockPixels 是 Android Native Development Kit (NDK) 中的一个函数,用于锁定一个 android.graphics.Bitmap 对象的像素数据,以便在 Native 代码中进行像素级别的操作。这个函数允许在 C 或 C++ 代码中直接访问 Android 应用中的位图像素数据,以便进行图像处理、渲染或其他图像相关的操作。最后记得调用AndroidBitmap_unlockPixels解锁。至于为什么是(R+G+B)/3,这个问题要问我为什么这么算,我能力有限教不了你们,你得问计算机图像处理学的专家,哈哈。当将彩色图像转换为黑白图像时,通常采用灰度化的方法,即将红、绿、蓝三个通道的数值取平均值,以获得灰度图像。因此,将RGB图像转换为黑白图像时,每个像素的灰度值通常是红、绿、蓝通道值的平均值,即(R+G+B)/3。

cpp 复制代码
#include <jni.h>
#include <string>
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <android/bitmap.h>

#define MAKE_RGB565(r, g, b) ((((r) >> 3) << 11) | (((g) >> 2) << 5) | ((b) >> 3))
#define MAKE_ARGB(a, r, g, b) ((a&0xff)<<24) | ((r&0xff)<<16) | ((g&0xff)<<8) | (b&0xff)

#define RGB565_R(p) ((((p) & 0xF800) >> 11) << 3)
#define RGB565_G(p) ((((p) & 0x7E0 ) >> 5)  << 2)
#define RGB565_B(p) ( ((p) & 0x1F  )        << 3)

#define RGB8888_A(p) (p & (0xff<<24) >> 24 )
#define RGB8888_R(p) (p & (0xff<<16) >> 16 )
#define RGB8888_G(p) (p & (0xff<<8)  >> 8 )
#define RGB8888_B(p) (p & (0xff) )

#define RGBA_A(p) (((p) & 0xFF000000) >> 24)
#define RGBA_R(p) (((p) & 0x00FF0000) >> 16)
#define RGBA_G(p) (((p) & 0x0000FF00) >>  8)
#define RGBA_B(p)  ((p) & 0x000000FF)
#define MAKE_RGBA(r, g, b, a) (((a) << 24) | ((r) << 16) | ((g) << 8) | (b))

extern "C" JNIEXPORT void JNICALL
Java_com_dorachat_myapplication_MainActivity_nativeProcessBitmap(JNIEnv *env,
                                                                 jobject instance,
                                                                 jobject bitmap) {

    if (bitmap == NULL) {
        return;
    }

    AndroidBitmapInfo bitmapInfo;
    memset(&bitmapInfo, 0, sizeof(bitmapInfo));
    // Need add "jnigraphics" into target_link_libraries in CMakeLists.txt
    AndroidBitmap_getInfo(env, bitmap, &bitmapInfo);
    // Lock the bitmap to get the buffer
    void *pixels = NULL;
    int res = AndroidBitmap_lockPixels(env, bitmap, &pixels);
    // From top to bottom
    int x = 0, y = 0;
    for (y = 0; y < bitmapInfo.height; ++y) {
        // From left to right
        for (x = 0; x < bitmapInfo.width; ++x) {
            int a = 0, r = 0, g = 0, b = 0;
            void *pixel = NULL;
            // Get each pixel by format
            if (bitmapInfo.format == ANDROID_BITMAP_FORMAT_RGBA_8888) {
                pixel = ((uint32_t *) pixels) + y * bitmapInfo.width + x;
                int r, g, b;
                uint32_t v = *((uint32_t *) pixel);
                r = RGB8888_R(v);
                g = RGB8888_G(v);
                b = RGB8888_B(v);
                int sum = r + g + b;
                *((uint32_t *) pixel) = MAKE_ARGB(0xff, sum / 3, sum / 3, sum / 3);
            } else if (bitmapInfo.format == ANDROID_BITMAP_FORMAT_RGB_565) {
                pixel = ((uint16_t *) pixels) + y * bitmapInfo.width + x;
                int r, g, b;
                uint16_t v = *((uint16_t *) pixel);
                r = RGB565_R(v);
                g = RGB565_G(v);
                b = RGB565_B(v);
                int sum = r + g + b;
                *((uint16_t *) pixel) = MAKE_RGB565(sum / 3, sum / 3, sum / 3);
            }
        }
    }
    AndroidBitmap_unlockPixels(env, bitmap);
}
效果演示

知道你们喜欢清纯的,来了。最后不忘留个赞吧。

相关推荐
2401_8979078624 分钟前
10天学会flutter DAY2 玩转dart 类
android·flutter
m0_748233641 小时前
【PHP】部署和发布PHP网站到IIS服务器
android·服务器·php
Yeats_Liao2 小时前
Spring 定时任务:@Scheduled 注解四大参数解析
android·java·spring
雾里看山4 小时前
【MySQL】 库的操作
android·数据库·笔记·mysql
水瓶丫头站住12 小时前
安卓APP如何适配不同的手机分辨率
android·智能手机
xvch13 小时前
Kotlin 2.1.0 入门教程(五)
android·kotlin
xvch16 小时前
Kotlin 2.1.0 入门教程(七)
android·kotlin
望风的懒蜗牛17 小时前
编译Android平台使用的FFmpeg库
android
浩宇软件开发17 小时前
Android开发,待办事项提醒App的设计与实现(个人中心页)
android·android studio·android开发
ac-er888818 小时前
Yii框架中的多语言支持:如何实现国际化
android·开发语言·php