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@nicwise
Last active November 13, 2018 08:17
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Scale and Rotate an image in iOS / MonoTouch, using the EXIF data
//MIT license
public static UIImage ScaleImage(UIImage image, int maxSize)
{
UIImage res;
using (CGImage imageRef = image.CGImage)
{
CGImageAlphaInfo alphaInfo = imageRef.AlphaInfo;
CGColorSpace colorSpaceInfo = CGColorSpace.CreateDeviceRGB();
if (alphaInfo == CGImageAlphaInfo.None)
{
alphaInfo = CGImageAlphaInfo.NoneSkipLast;
}
int width, height;
width = imageRef.Width;
height = imageRef.Height;
if (height >= width)
{
width = (int)Math.Floor((double)width * ((double)maxSize / (double)height));
height = maxSize;
}
else
{
height = (int)Math.Floor((double)height * ((double)maxSize / (double)width));
width = maxSize;
}
CGBitmapContext bitmap;
if (image.Orientation == UIImageOrientation.Up || image.Orientation == UIImageOrientation.Down)
{
bitmap = new CGBitmapContext(IntPtr.Zero, width, height, imageRef.BitsPerComponent, imageRef.BytesPerRow, colorSpaceInfo, alphaInfo);
}
else
{
bitmap = new CGBitmapContext(IntPtr.Zero, height, width, imageRef.BitsPerComponent, imageRef.BytesPerRow, colorSpaceInfo, alphaInfo);
}
switch (image.Orientation)
{
case UIImageOrientation.Left:
bitmap.RotateCTM((float)Math.PI / 2);
bitmap.TranslateCTM(0, -height);
break;
case UIImageOrientation.Right:
bitmap.RotateCTM(-((float)Math.PI / 2));
bitmap.TranslateCTM(-width, 0);
break;
case UIImageOrientation.Up:
break;
case UIImageOrientation.Down:
bitmap.TranslateCTM(width, height);
bitmap.RotateCTM(-(float)Math.PI);
break;
}
bitmap.DrawImage(new Rectangle(0, 0, width, height), imageRef);
res = UIImage.FromImage(bitmap.ToImage());
bitmap = null;
}
return res;
}
@mjracca
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mjracca commented Jun 3, 2013

Thanks!! Rotation works perfectly!

@tonyfonager
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You are the champ - thanks ;-)

@schmidan
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schmidan commented Dec 6, 2013

I was building the same thing but got problems with Orientation. Your Snipped works perfectly. Thanks a bunch!

@adilo
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adilo commented Dec 25, 2013

It worked like a charm ! Thank you !

@felixcollins
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Note that the BytesPerRow is not being recalculated for the CGBitmapContext ctor despite scaling the size. This can cause an exception if the row width is not great enough ("CGBitmapContextCreate: invalid data bytes/row:"). Set it to 0 instead of imageRef.BytesPerRow to let CoreGraphics calculate it. Thanks Mr Wise!

@jacksierkstra
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This works very good! I wonder if there is a version for Monodroid aswell?

@yehe01
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yehe01 commented Aug 26, 2016

Thanks.

@armaganX
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What is the maxSize parameter for no changing photo's resolution ?

@drew-neely
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drew-neely commented Jun 18, 2018

Thanks! This helped me a ton.

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