Resize and saving an image to disk in Monotouch - objective-c

Question

I'm trying to resize an image loaded from disk - a JPG or PNG (I don't know the format when I load it) - and then save it back to disk.
I've got the following code which I've tried to port from objective-c, however I've got stuck on the last parts. Original Objective-C.
This may not be the best way of achieving what I want to do - any solution is fine for me.
int width = 100;
int height = 100;
using (UIImage image = UIImage.FromFile(filePath))
{
CGImage cgimage = image.CGImage;
CGImageAlphaInfo alphaInfo = cgimage.AlphaInfo;
if (alphaInfo == CGImageAlphaInfo.None)
alphaInfo = CGImageAlphaInfo.NoneSkipLast;
CGBitmapContext context = new CGBitmapContext(IntPtr.Zero,
width,
height,
cgimage.BitsPerComponent,
4 * width,
cgimage.ColorSpace,
alphaInfo);
context.DrawImage(new RectangleF(0, 0, width, height), cgimage);
/*
Not sure how to convert this part:
CGImageRef ref = CGBitmapContextCreateImage(bitmap);
UIImage* result = [UIImage imageWithCGImage:ref];
CGContextRelease(bitmap); // ok if NULL
CGImageRelease(ref);
*/
}

Answer 1

In the upcoming MonoTouch we will have a scale method, this is its implementation in UIImage.cs:
public UIImage Scale (SizeF newSize)
{
UIGraphics.BeginImageContext (newSize);
var context = UIGraphics.GetCurrentContext ();
context.TranslateCTM (0, newSize.Height);
context.ScaleCTM (1f, -1f);
context.DrawImage (new RectangleF (0, 0, newSize.Width, newSize.Height), CGImage);
var scaledImage = UIGraphics.GetImageFromCurrentImageContext();
UIGraphics.EndImageContext();
return scaledImage;
}
Adjusted to be reused outside of MonoTouch:
public static UIImage Scale (UIImage source, SizeF newSize)
{
UIGraphics.BeginImageContext (newSize);
var context = UIGraphics.GetCurrentContext ();
context.TranslateCTM (0, newSize.Height);
context.ScaleCTM (1f, -1f);
context.DrawImage (new RectangleF (0, 0, newSize.Width, newSize.Height), source.CGImage);
var scaledImage = UIGraphics.GetImageFromCurrentImageContext();
UIGraphics.EndImageContext();
return scaledImage;
}

Answer 2

public static UIImage EditPhoto(int iMode, UIImage origImg)
{
SizeF newSize;
if (iMode == 1 || iMode == 2)
newSize = new SizeF(origImg.Size.Height, origImg.Size.Width);
else
newSize = origImg.Size;
UIGraphics.BeginImageContext(newSize);
CGContext ctx = UIGraphics.GetCurrentContext();
switch (iMode)
{
case 1: // Rotate counter-clockwise 90 degrees
ctx.TranslateCTM(origImg.Size.Height, origImg.Size.Width);
ctx.ScaleCTM(1f, -1f);
ctx.RotateCTM(1.57079633f); // angle is in radians
break;
case 2: // Rotate clockwise 90 degrees
ctx.ScaleCTM(1f, -1f);
ctx.RotateCTM(-1.57079633f); // angle is in radians
break;
case 3: // Flip vertical
// Do nothing. The image comes out flipped vertically because Core Graphics / OpenTK uses cartesian coordinates
break;
case 4: // Flip horizontal
ctx.TranslateCTM(newSize.Width, newSize.Height);
ctx.ScaleCTM(-1f, -1f);
break;
default: // Return unchanged image
ctx.TranslateCTM(0, origImg.Size.Height);
ctx.ScaleCTM(1f, -1f);
break;
}
ctx.DrawImage(new RectangleF(0, 0, origImg.Size.Width, origImg.Size.Height), origImg.CGImage);
UIImage resImg = UIGraphics.GetImageFromCurrentImageContext();
UIGraphics.EndImageContext();
return resImg;
}

Answer 3

To get an UIImage from context all you need to do is:
UIImage* result = UIImage.FromImage(context.ToImage());