CODEWITHSUNDEEP
iosimageimage-processingios5
user1139699
user1139699

Reputation: 188

How to add colors into pixel by pixel on image on iphone?

This is my first assignment about image processing. I'm assuming index of each pixel on output image are represented as matrix below:

00 01 02 03 04 05

10 11 12 13 14 15

20 21 22 23 24 25

At each index of output image I have different color to draw on. For ex, at index 00 I have redcolor available to put there and so on with other indexes. My question is how can I draw these color into the indexes to create the output image?

Update

This is what I have right now:

 inputImgAvg //Image for processing
 CGContextRef context = UIGraphicsGetCurrentContext();

 float  yy = groutW / 2;            // skip over grout on edge
     float stride =(int) (tileW + groutW +0.5);
        for(int y=0; y<tilesY; y++) {               //Number tile in Y direction
            float xx = groutW / 2 ;         // skip over grout on edge
            for(int x=0; x<tilesX; x++) {
                tileRGB = [inputImgAvg colorAtPixel:CGPointMake(x,y)];

                //Right here I'm checking tileRGB with list of available color
                //Find out the closest color 
                //Now i'm just checking with greenColor

                // best matching tile is found in idx position in vector;
                // scale and copy it into proper location in the output
                CGContextSetFillColor(context, CGColorGetComponents( [[UIColor greenColor] CGColor]));

But I got this error. Can you point out what did I do wrong?

<Error>: CGContextSetFillColor: invalid context 0x0
<Error>: CGContextFillRects: invalid context 0x0

Upvotes: 0

Views: 1993

Answers (1)

Nick Lockwood
Nick Lockwood

Reputation: 41005

This thread answers the question:

http://www.iphonedevsdk.com/forum/iphone-sdk-development/34247-cgimage-pixel-array.html

Create a CGContext using CGBitmapContextCreate, which lets you supply the data for the image. You can then write pixels into the data using a pointer and setting the bytes yourself.

Once you are done, use UIGraphicsGetImageFromCurrentContext() or equivalent to grab the context data out into a UIImage object.

If that all seems a bit low-level, another option would be to just create a CGContext and draw 1x1 rectangles into it. It won't be amazingly fast, but it won't be as slow as you think because CG functions are all pure C and any redundancy gets optimised out by the compiler:

//create drawing context
UIGraphicsBeginImageContextWithOptions(CGSizeMake(width, height), NO, 0.0f);
CGContextRef context = UIGraphicsGetCurrentContext();  

//draw pixels
for (int x = 0; x < width; x++)
{
   for (int y = 0; y < height; y++)
   {
      CGContextSetFillColor( ... your color here ... );
      CGContextFillRect(context, CGRectMake(x, y, 1.0f, 1.0f));
   }
}

//capture resultant image
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

Upvotes: 2

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