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Encontrar el cuadrado centrado más grande de un paisaje o un UII de retrato y escalarlo a un tamaño

Question

Necesito encontrar el cuadrado centrado más grande a partir de un retrato o una imagen de paisaje a escala. Por ejemplo, si obtengo una imagen de tamaño 1200x800 y necesito obtener el cuadrado centrado hasta el tamaño de 300x300.

Answer 1

Encontré una respuesta sobre esta pregunta en que ha sido ampliamente copiada. Sin embargo, esa respuesta es incorrecta, así que quiero publicar la respuesta correcta, que es la siguiente:

+ (UIImage*) cropBiggestCenteredSquareImageFromImage:(UIImage*)image withSide:(CGFloat)side
{
// Get size of current image
CGSize size = [image size];
if( size.width == size.height && size.width == side){
return image;
}
CGSize newSize = CGSizeMake(side, side);
double ratio;
double delta;
CGPoint offset;
//make a new square size, that is the resized imaged width
CGSize sz = CGSizeMake(newSize.width, newSize.width);
//figure out if the picture is landscape or portrait, then
//calculate scale factor and offset
if (image.size.width > image.size.height) {
ratio = newSize.height / image.size.height;
delta = ratio*(image.size.width - image.size.height);
offset = CGPointMake(delta/2, 0);
} else {
ratio = newSize.width / image.size.width;
delta = ratio*(image.size.height - image.size.width);
offset = CGPointMake(0, delta/2);
}
//make the final clipping rect based on the calculated values
CGRect clipRect = CGRectMake(-offset.x, -offset.y,
(ratio * image.size.width),
(ratio * image.size.height));
//start a new context, with scale factor 0.0 so retina displays get
//high quality image
if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)]) {
UIGraphicsBeginImageContextWithOptions(sz, YES, 0.0);
} else {
UIGraphicsBeginImageContext(sz);
}
UIRectClip(clipRect);
[image drawInRect:clipRect];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}

La respuesta incorrecta que encontré antes es la siguiente:

+ (UIImage*) cropBiggestCenteredSquareImageFromImage:(UIImage*)image withSide:(CGFloat)side
{
// Get size of current image
CGSize size = [image size];
if( size.width == size.height && size.width == side){
return image;
}
CGSize newSize = CGSizeMake(side, side);
double ratio;
double delta;
CGPoint offset;
//make a new square size, that is the resized imaged width
CGSize sz = CGSizeMake(newSize.width, newSize.width);
//figure out if the picture is landscape or portrait, then
//calculate scale factor and offset
if (image.size.width > image.size.height) {
ratio = newSize.width / image.size.width;
delta = (ratio*image.size.width - ratio*image.size.height);
offset = CGPointMake(delta/2, 0);
} else {
ratio = newSize.width / image.size.height;
delta = (ratio*image.size.height - ratio*image.size.width);
offset = CGPointMake(0, delta/2);
}
//make the final clipping rect based on the calculated values
CGRect clipRect = CGRectMake(-offset.x, -offset.y,
(ratio * image.size.width) + delta,
(ratio * image.size.height) + delta);
//start a new context, with scale factor 0.0 so retina displays get
//high quality image
if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)]) {
UIGraphicsBeginImageContextWithOptions(sz, YES, 0.0);
} else {
UIGraphicsBeginImageContext(sz);
}
UIRectClip(clipRect);
[image drawInRect:clipRect];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}

El problema con este código es que no se recorta correctamente.

Ambos códigos se pueden probar en la siguiente imagen: https://s3.amazonaws.com/anandprakash/ImageWithPixelGrid.jpg

Corregir Algo genera la siguiente imagen en la url base anterior: https://s3.amazonaws.com/anandprakash/ScreenshotCorrectAlgo.png

Wrong Algo genera la siguiente imagen en la url base anterior: fíjate en los 50 píxeles adicionales en el ancho de cada lado. https://s3.amazonaws.com/anandprakash/ScreenshotWrongAlgo.png

Answer 2

La misma respuesta anterior que una extensión Swift en UIImage:

private extension UIImage {
func cropBiggestCenteredSquareImage(withSide side: CGFloat) -> UIImage {
if self.size.height == side && self.size.width == side {
return self
}
let newSize = CGSizeMake(side, side)
let ratio: CGFloat
let delta: CGFloat
let offset: CGPoint
if self.size.width > self.size.height {
ratio = newSize.height / self.size.height
delta = ratio * (self.size.width - self.size.height)
offset = CGPointMake(delta / 2, 0)
}
else {
ratio = newSize.width / self.size.width
delta = ratio * (self.size.height - self.size.width)
offset = CGPointMake(0, delta / 2)
}
let clipRect = CGRectMake(-offset.x, -offset.y, ratio * self.size.width, ratio * self.size.height)
if UIScreen.mainScreen().respondsToSelector(#selector(NSDecimalNumberBehaviors.scale)) {
UIGraphicsBeginImageContextWithOptions(newSize, true, 0.0)
} else {
UIGraphicsBeginImageContext(newSize);
}
UIRectClip(clipRect)
self.drawInRect(clipRect)
let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return newImage
}
}