iOS滤镜实现之Nashville【instagram】

Nashville是Instagram众多滤镜中最惊艳的一款，独特的奶昔色调赋予照片童话般的唯美感觉。
适用范围：营造浪漫唯美的感觉。
的确如此啊
有2张输入图像

顶点着色
有2组坐标
NSString *const kGPUImageTwoInputTextureVertexShaderString = SHADER_STRING

(
 attribute vec4 position;
//输入的坐标
 attribute vec4 inputTextureCoordinate;
 attribute vec4 inputTextureCoordinate2;
 //输出的坐标，与片段着色器
 varying vec2 textureCoordinate;
 varying vec2 textureCoordinate2;

 void main()
 {
//告诉片段着色器，我在处理哪些像素
     gl_Position = position;
     textureCoordinate = inputTextureCoordinate.xy;
     textureCoordinate2 = inputTextureCoordinate2.xy;
 }
);

片段着色

NSString *const kFWNashvilleShaderString = SHADER_STRING
(
 precision lowp float;

 varying highp vec2 textureCoordinate;

 uniform sampler2D inputImageTexture;
 uniform sampler2D inputImageTexture2;

 void main()
 {
     vec3 texel = texture2D(inputImageTexture, textureCoordinate).rgb;
     texel = vec3(
                  texture2D(inputImageTexture2, vec2(texel.r, .16666)).r,
                  texture2D(inputImageTexture2, vec2(texel.g, .5)).g,
                  texture2D(inputImageTexture2, vec2(texel.b, .83333)).b);
     gl_FragColor = vec4(texel, 1.0);
 }
 );

 初始化

- (id)init
{
    if (!(self = [super init]))
    {
        return nil;
    }

    UIImage *image = [UIImage imageNamed:@"nashvilleMap.png"];

    imageSource = [[GPUImagePicture alloc] initWithImage:image];
    FWFilter1 *filter = [[FWFilter1 alloc] init];

    [self addFilter:filter];
    [imageSource addTarget:filter atTextureLocation:];
    [imageSource processImage];

    self.initialFilters = [NSArray arrayWithObjects:filter, nil];
    self.terminalFilter = filter;

    return self;
}

//
//  FWNashvilleFilter.h
//  FWMeituApp
//
//  Created by hzkmn on 16/1/8.
//  Copyright © 2016年 ForrestWoo co,.ltd. All rights reserved.
//

#import "GPUImageTwoInputFilter.h"

@interface FWFilter1 : GPUImageTwoInputFilter

@end

@interface FWNashvilleFilter : GPUImageFilterGroup
{
    GPUImagePicture *imageSource ;
}

@end

//
//  FWNashvilleFilter.m
//  FWMeituApp
//
//  Created by hzkmn on 16/1/8.
//  Copyright © 2016年 ForrestWoo co,.ltd. All rights reserved.
//

#import "FWNashvilleFilter.h"

NSString *const kFWNashvilleShaderString = SHADER_STRING
(
 precision lowp float;

 varying highp vec2 textureCoordinate;

 uniform sampler2D inputImageTexture;
 uniform sampler2D inputImageTexture2;

 void main()
 {
     vec3 texel = texture2D(inputImageTexture, textureCoordinate).rgb;
     texel = vec3(
                  texture2D(inputImageTexture2, vec2(texel.r, .)).r,
                  texture2D(inputImageTexture2, vec2(texel.g, .)).g,
                  texture2D(inputImageTexture2, vec2(texel.b, .)).b);
     gl_FragColor = vec4(texel, 1.0);
 }
 );

@implementation FWFilter1

- (id)init;
{
    if (!(self = [super initWithFragmentShaderFromString:kFWNashvilleShaderString]))
    {
        return nil;
    }

    return self;
}

@end

@implementation FWNashvilleFilter

- (id)init
{
    if (!(self = [super init]))
    {
        return nil;
    }

    UIImage *image = [UIImage imageNamed:@"nashvilleMap.png"];

    imageSource = [[GPUImagePicture alloc] initWithImage:image];
    FWFilter1 *filter = [[FWFilter1 alloc] init];

    [self addFilter:filter];
    [imageSource addTarget:filter atTextureLocation:];
    [imageSource processImage];

    self.initialFilters = [NSArray arrayWithObjects:filter, nil];
    self.terminalFilter = filter;

    return self;
}

@end

原图

效果图

完整项目代码查看我在github

我们再来看几组效果