Question

I’m programming on objective-c. I have an image a line (see below) (1 x 30) pixels.

How can I get a UIImage (50 x 30) (see below) from this line?

Answer 1

Create a CGBitmapContext with size of 50 * 30 than you can just draw that image on the context by using CGContextDrawImage.

After that use CGBitmapContextCreateImage and [UIImage imageWithCGImage:] to create the UIImage

CGContextRef CreateBitmapContext(int pixelsWide, int pixelsHigh)
{
    CGContextRef    context = NULL;
    CGColorSpaceRef colorSpace;
    int             bitmapByteCount;
    int             bitmapBytesPerRow;

    bitmapBytesPerRow   = (pixelsWide * 4); // RGBA
    bitmapByteCount     = (bitmapBytesPerRow * pixelsHigh);

    colorSpace = CGColorSpaceCreateDeviceRGB();
    context = CGBitmapContextCreate (NULL,
                                     pixelsWide,
                                     pixelsHigh,
                                     8,      // bits per component
                                     bitmapBytesPerRow,
                                     colorSpace,
                                     kCGImageAlphaPremultipliedLast);
    NSCAssert(context != NULL, @"cannot create bitmap context");
    CGColorSpaceRelease( colorSpace );

    return context;
}

CGContextRef context = CreateBitmapContext(50, 30);
UIImage *yourLineImage = ...;
CGImageRef cgImg = [yourLineImage CGImage];
for (int i = 0; i < 50; i++) {
    CGRect rect;
    rect.origin.x = i;
    rect.origin.y = 0;
    rect.size.width = 1;
    rect.size.height = 30;
    CGContextDrawImage(context, rect, cgImg);
}
CGImageRef output = CGBitmapContextCreateImage(context);
UIImage *result = [UIImage imageWithCGImage:output];