polaroid filter from UIImage

Question

I am trying to implement some image filters, like polaroid, in iphone. I searched on how to filter an existing UIImage to convert it into a polaroid style and come across this stackoverflow link. Taking the answer there as a starting point, I looped through each pixel of the image, taking RGB values, and converted them to HSV, up to this point I have been successful. So this is what I have done (anyone is free to point any mistakes..)

double minRGB(double r, double g, double b){
    if (r < g){
        if (r < b){
            return r;
        }else {
            return b;
        }
    }else { 
        if (g < b){
            return g;
        }else{
            return b;
        }
    }
}



double maxRGB(double r, double g, double b){
    if (r > g){
        if (r > b){
            return r;
        }else {
            return b;
        }
    }else { 
        if (g > b){
            return g;
        }else {
            return b;
        }
    }
}

void rgbToHsv(double redIn,double greenIn,double blueIn,double *hue,double *saturation,double* value){
    double min,max,delta;

    min                         =   minRGB(redIn,greenIn,blueIn);
    max                         =   maxRGB(redIn,greenIn,blueIn);
    *value                      =   max;
    delta                       =   max - min;
    if (max != 0) {
        *saturation             =   delta/max;
    }else {
        *saturation             =   0;
        *hue                        =   -1.0;
        return ;
    }
    if (redIn == max) {
        *hue                    =   (greenIn - blueIn)/delta;
    }else if (greenIn == max) {
        *hue                    =   2 + (blueIn - redIn)/delta;
    }else {
        *hue                    =   4 + (redIn - greenIn)/delta;
    }
    *hue                        *=  60.0;
    if (*hue < 0) {
        *hue                    +=  360.0;
    }
}

void hsvToRgb(double h,double s, double v, double *r,double *g, double *b){
    int i;
    float f, p, q, t;
    if( s == 0 ) {
        // achromatic (grey)
        *r = *g = *b = v;
        return;
    }
    h                           /=  60;         // sector 0 to 5
    i                           =   floor( h );
    f                           =   h - i;          // factorial part of h
    p                           =   v * ( 1 - s );
    q                           =   v * ( 1 - s * f );
    t                           =   v * ( 1 - s * ( 1 - f ) );
    switch( i ) {
        case 0:
            *r = v;
            *g = t;
            *b = p;
            break;
        case 1:
            *r = q;
            *g = v;
            *b = p;
            break;
        case 2:
            *r = p;
            *g = v;
            *b = t;
            break;
        case 3:
            *r = p;
            *g = q;
            *b = v;
            break;
        case 4:
            *r = t;
            *g = p;
            *b = v;
            break;
        default:        // case 5:
            *r = v;
            *g = p;
            *b = q;
            break;
    }
}


-(void)makeImagePolaroid:(UIImage*)myImage{
CGImageRef originalImage        =   [myImage CGImage];
CGColorSpaceRef colorSpace      =   CGColorSpaceCreateDeviceRGB();
CGContextRef bitmapContext      =   CGBitmapContextCreate(NULL,CGImageGetWidth(originalImage),CGImageGetHeight(originalImage),8,CGImageGetWidth(originalImage)*4,colorSpace,kCGImageAlphaPremultipliedLast);
CGColorSpaceRelease(colorSpace);
CGContextDrawImage(bitmapContext, CGRectMake(0, 0, CGBitmapContextGetWidth(bitmapContext), CGBitmapContextGetHeight(bitmapContext)), originalImage);
UInt8 *data                     =   CGBitmapContextGetData(bitmapContext);
int numComponents               =   4;
int bytesInContext              =   CGBitmapContextGetHeight(bitmapContext) * CGBitmapContextGetBytesPerRow(bitmapContext);
double redIn, greenIn, blueIn,alphaIn;
double hue,saturation,value;

for (int i = 0; i < bytesInContext; i += numComponents) {
    redIn                       =   (double)data[i]/255.0;
    greenIn                     =   (double)data[i+1]/255.0;
    blueIn                      =   (double)data[i+2]/255.0;
    alphaIn                     =   (double)data[i+3]/255.0;

    rgbToHsv(redIn,greenIn,blueIn,&hue,&saturation,&value);

    hue                         =   hue * 0.7;
    if (hue > 360) {
        hue                     =   360;
    }

    saturation                  =   saturation *1.3;
    if (saturation > 1.0) {
        saturation              =   1.0;
    }

    value                       =   value * 0.8;
    if (value > 1.0) {
        value                   =   1.0;
    }

    hsvToRgb(hue,saturation,value,&redIn,&greenIn,&blueIn);
    data[i]                     =   redIn * 255.0;
    data[i+1]                   =   greenIn * 255.0;
    data[i+2]                   =   blueIn * 255.0;
}
CGImageRef outImage             =   CGBitmapContextCreateImage(bitmapContext);
myImage                         =   [UIImage imageWithCGImage:outImage];
CGImageRelease(outImage);
return myImage;
}

Now my idea about image processing is very childish (not even amateurish). I read this and tried to adjust the saturation and hue to see if I can get a polaroid effect..I think I am missing something, for I got every effect on earth other than a polaroid (saying that I havent got anything)..

1. Is there any document on net (or books) which tells about image filtering on a programmers point of view? (and not on a designers point of view and without a photoshop screenshot)
2. What is the hue, saturation, value difference I have to make on a pixel so that I can make it polaroid?
3. And third, Am I on the right track?

Thanks in advance..

Answer 1

This might be helpful, from Camera+ taking filters from photoshop and reproducing them for iOS.

http://taptaptap.com/blog/creating-a-camera-plus-fx/

Answer 2

     int step=10;// variable value that changes the level of saturation

int red = pixelRedVal;
int green = pixelGreenVal;
int blue = pixelBlueVal;

int avg = (red + green + blue) / 3;

pixelBuf[r] = SAFECOLOR((avg + step * (red - avg)));
pixelBuf[g] = SAFECOLOR((avg + step * (green - avg)));
pixelBuf[b] = SAFECOLOR((avg + step * (blue - avg)));
where SAFECOLOR is a macro

define SAFECOLOR(color) MIN(255,MAX(0,color))
and for Brightness int step=10;// variable value that changes the level of saturation

int red = pixelRedVal;
int green = pixelGreenVal;
int blue = pixelBlueVal;


pixelBuf[r] = SAFECOLOR(red * step);
pixelBuf[g] = SAFECOLOR(green * step);
pixelBuf[b] = SAFECOLOR(blue * step);




You can simply use this: with different parameters

// Note: the hue input ranges from 0.0 to 1.0, both red.  Values outside this range will be clamped to 0.0 or 1.0.
    //Polaroid with HSB parameter

   - (UIImage*) polaroidishEffectWithHue:(CGFloat)hue saturation:(CGFloat)sat brightness:(CGFloat)bright  alpha:(CGFloat)alpha
  {

   // Find the image dimensions.
    CGSize imageSize = [self size];
    CGRect imageExtent = CGRectMake(0,0,imageSize.width,imageSize.height);

    // Create a context containing the image.
    UIGraphicsBeginImageContext(imageSize);
    CGContextRef context = UIGraphicsGetCurrentContext();
    [self drawAtPoint:CGPointMake(0,0)];

    // Draw the hue on top of the image.
    CGContextSetBlendMode(context, kCGBlendModeHue);
    [[UIColor colorWithHue:hue saturation:sat brightness:bright alpha:alpha] set];
    UIBezierPath *imagePath = [UIBezierPath bezierPathWithRect:imageExtent];
    [imagePath fill];

    // Retrieve the new image.
    UIImage *result = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return result;
}