Summary of image compression methods in iOS

There are two simple ways to read picture data on the iphone: UIImageJPEGRepresentation and Uiimagepngrepresentation. The UIImageJPEGRepresentation function requires two parameters: a picture's reference and a compression factor. Uiimagepngrepresentation only need picture references as parameters.

Method One:

The code is as follows:

-(uiimage*) Scalefromimage: (uiimage*) Image scaledtosize: (cgsize) newsize

{

Cgsize imagesize = image.size;

CGFloat width = imagesize.width;

CGFloat height = imagesize.height;

if (width <= newsize.width && height <= newsize.height) {

return image;

}

if (width = 0 | | height = = 0) {

return image;

}

CGFloat widthfactor = newsize.width/width;

CGFloat heightfactor = newsize.height/height;

CGFloat scalefactor = (widthfactor

CGFloat scaledwidth = width * scalefactor;

CGFloat scaledheight = height * scalefactor;

Cgsize targetsize = Cgsizemake (scaledwidth,scaledheight);

Uigraphicsbeginimagecontext (targetsize);

[Image Drawinrect:cgrectmake (0,0,scaledwidth,scaledheight)];

uiimage* newimage = Uigraphicsgetimagefromcurrentimagecontext ();

Uigraphicsendimagecontext ();

return newimage;

}

Method Two:

. h Specific Code

The code is as follows:

#import

@interface UIImage (Uiimageext)

-(UIImage *) Scaletosize: (uiimage *) img Size: (cgsize) size;

-(UIImage *) Imagebyscalingandcroppingforsize: (cgsize) targetsize;

@end

. M specific Code

The code is as follows:

#import "UIImageExt.h"

@implementation UIImage (Uiimageext)

-(UIImage *) Scaletosize: (uiimage *) img Size: (cgsize) size{

Create a bitmap context

and set it to be the context that is currently in use

Uigraphicsbeginimagecontext (size);

Draw a picture that changes size

[img drawinrect:cgrectmake (0, 0, Size.width, size.height)];

Create a picture that changes size from the current context

uiimage* scaledimage = Uigraphicsgetimagefromcurrentimagecontext ();

Make the current context out of the stack

Uigraphicsendimagecontext ();

Returns a new resized picture

return scaledimage;

}

-(uiimage*) Imagebyscalingandcroppingforsize: (cgsize) targetsize

{

UIImage *sourceimage = self;

UIImage *newimage = nil;

Cgsize imagesize = sourceimage.size;

CGFloat width = imagesize.width;

CGFloat height = imagesize.height;

CGFloat targetwidth = targetsize.width;

CGFloat targetheight = targetsize.height;

CGFloat scalefactor = 0.0;

CGFloat scaledwidth = targetwidth;

CGFloat scaledheight = targetheight;

Cgpoint thumbnailpoint = Cgpointmake (0.0,0.0);

if (Cgsizeequaltosize (imagesize, targetsize) = NO)

{

CGFloat widthfactor = targetwidth/width;

CGFloat heightfactor = targetheight/height;

if (Widthfactor > Heightfactor)

Scalefactor = Widthfactor; Scale to fit height

Else

Scalefactor = Heightfactor; Scale to fit width

Scaledwidth = width * scalefactor;

Scaledheight = height * scalefactor;

Center the image

if (Widthfactor > Heightfactor)

{

Thumbnailpoint.y = (targetheight-scaledheight) * 0.5;

}

Else

if (Widthfactor < Heightfactor)

{

Thumbnailpoint.x = (targetwidth-scaledwidth) * 0.5;

}

}

Uigraphicsbeginimagecontext (targetsize); This would crop

CGRect thumbnailrect = Cgrectzero;

Thumbnailrect.origin = Thumbnailpoint;

ThumbnailRect.size.width = Scaledwidth;

ThumbnailRect.size.height = Scaledheight;

[Sourceimage Drawinrect:thumbnailrect];

NewImage = Uigraphicsgetimagefromcurrentimagecontext ();

if (newimage = = nil)

NSLog (@ "Could not scale image");

Pop the context to get back to the default

Uigraphicsendimagecontext ();

return newimage;

}

@end

Method Three: (the method used in my project)

The code is as follows:

-(UIImage *) Imagecompressforwidth: (UIImage *) sourceimage targetwidth: (cgfloat) Definewidth

{

Cgsize imagesize = sourceimage.size;

CGFloat width = imagesize.width;

CGFloat height = imagesize.height;

CGFloat targetwidth = definewidth;

CGFloat targetheight = (targetwidth/width) * height;

Uigraphicsbeginimagecontext (Cgsizemake (Targetwidth, targetheight));

[Sourceimage Drawinrect:cgrectmake (0,0,targetwidth, targetheight)];

uiimage* newimage = Uigraphicsgetimagefromcurrentimagecontext ();

Uigraphicsendimagecontext ();

return newimage;

}

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