UIImage

UIImage is an Objective-C class that represents a bitmap image.

Undocumented methods

Precomposed icon

From left to right: The original image; _applicationIconImagePrecomposed:NO; _applicationIconImagePrecomposed:YES; _smallApplicationIconImagePrecomposed:NO; _smallApplicationIconImagePrecomposed:YES

Signature	-(UIImage*)_applicationIconImageForFormat:(int)format precomposed:(BOOL)precomposed scale:(CGFloat)scale;
Available in	4.0 –

Signature	-(UIImage*)_applicationIconImageForFormat:(int)format precomposed:(BOOL)precomposed;
Available in	3.2 –

Signature	-(UIImage*)_applicationIconImagePrecomposed:(BOOL)precomposed;
Available in	2.0 – 4.0

Signature	-(UIImage*)_smallApplicationIconImagePrecomposed:(BOOL)precomposed;
Available in	2.0 – 3.1

These methods resize an image to icon size, clip out a rounded rectangle, draw shadows and apply a glossy overlay if required (when precomposed == NO), so that it resembles an icon.

Format	Size		MobileIcons variant			Description
	iPhone	iPad	iPhone	iPad 2x	iPad 1x
0	29×29	29×29	4	17	4
1	29×29	50×50	2	16	3	the small icon that appears in Spotlight
2	59×62	74×78	0	15	1	the large icon that appears in home screen (default)
3	44×45	74×78	22	23	1	for use in GameCenter (?)
4	59×62	74×78	24	25	26	in gray scale
5	31×37	64×64	18	19	5	document-like picture filled with the specified image
6	31×37	64×64	20	21	7	document-like picture with a small icon

The rendering of icon is actually done by MobileIcons.

If the input image is rectangular, the largest square portion in the top-left corner will be used.

Example:

@interface UIImage (privateAPI)
-(UIImage*)_applicationIconImagePrecomposed:(BOOL)precomposed;
@end
...
UIImage *regularIcon = [UIImage imageNamed:@"regularIcon.png"];
UIImage *renderedIcon = [regularIcon _applicationIconImageForFormat:2 precomposed:NO];
NSData  *pngData = UIImagePNGRepresentation( renderedIcon );
[pngData writeToFile:@"/tmp/roundedIcon.png" atomically:YES];

_flatImageWithWhite:alpha:

Signature	-(UIImage*)_flatImageWithWhite:(CGFloat)white alpha:(CGFloat)alpha;
Available in	2.0 –

Create an image having the same size as the original image, but filled with the solid color as the parameters.

_bezeledImageWithRed:green:blue:alpha:

Signature	-(UIImage*) _bezeledImageWithRed:(CGFloat)red green:(CGFloat)green blue:(CGFloat)blue alpha:(CGFloat)alpha;
Available in	2.0 – 3.1

Create a solid white image having the same size as the original image, and then stroke the top 1px edge by the specified color.

_imageScaledToSize:interpolationQuality: & _imageScaledToProportion:interpolationQuality:

Signature	-(UIImage*)_imageScaledToSize:(CGSize)newSize interpolationQuality:(CGInterpolationQuality)quality;
Available in	2.0 – 3.2

Signature	-(UIImage*)_imageScaledToProportion:(CGFloat)scale interpolationQuality:(CGInterpolationQuality)quality;
Available in	2.0 –

Rescale the image to the new size.

+kitImageNamed:

Signature	+(UIImage*)kitImageNamed:(NSString*)name;
Available in	2.0 –

Equivalent to _UIImageWithName(name).

+defaultDesktopImage

Signature	+(UIImage*)defaultDesktopImage;
Available in	2.0 – 4.1

Return the user's lock screen image.

+setDesktopImageData:

Signature	+(void)setDesktopImageData:(NSData*)jpegData;
Available in	2.0 – 3.2

Signature	+(void)setDesktopImageData:(NSData*)data composedPortraitImageData:(NSData*)data2 composedLandscapeImageData:(NSData*)data3 forVariant:(int)variant;
Available in	4.0 – 4.1

Replace the user's lock screen image by the given JPEG data.

+ _deviceSpecificImageNamed: (inBundle:)

Signature	+(UIImage *) _deviceSpecificImageNamed:(NSString *)

Signature	+(UIImage *) _deviceSpecificImageNamed:(NSString *) inBundle:(NSBundle *)

Like +imageNamed:(inBundle:) but with support for special longphone images (-568h)

Undocumented C functions

_UIImageWithName

Signature	UIImage* _UIImageWithName(NSString* name);
Available in	2.0 –

Obtain a built-in image. The name are stored in UIKit.framework/*.artwork. There are various ways to extract this information. A list of image names may also be helpful: 6.0, 2.0.

UIImageDataWriteToSavedPhotosAlbum

Signature	void UIImageDataWriteToSavedPhotosAlbum(NSData* imageData, id target, SEL selector, void* context);
Available in	3.1 –

Write the image data to photos album. This is similar to UIImageWriteToSavedPhotosAlbum function in the SDK, except that you can choose the image format (the extension will always be *.jpg, however).

UIGetScreenImage

Signature	CGImageRef UIGetScreenImage();
Available in	2.0 –

Signature	CGImageRef UICreateScreenImage();
Available in	3.2 –

"Print screen" and returns the image. Note that this is a CGImage, so you need to convert it to a UIImage with +[UIImage imageWithCGImage:].

Note that, although being a "Get" function, the returned image actually has retain count of +1, and the caller (you) are responsible to CGImageRelease it.

This function can be used for SDK apps between 2009 December and 2010 July

In firmware 3.2, UIGetScreenImage becomes an alias of the more appropriately-named UICreateScreenImage.

In arm64 version of iOS 7, the UIGetScreenImage was removed.

_UICreateScreenUIImage

Signature	UIImage* _UICreateScreenUIImage();
Available in	? –

Returns an image containing the contents of the screen. While similar in function to UIGetScreenImage, it uses the much faster CARenderServerRenderDisplay to perform the capture.

References

• Official documentation: http://developer.apple.com/iphone/library/documentation/uikit/reference/UIImage_Class/Reference/Reference.html
• Extra header: http://github.com/kennytm/iphone-private-frameworks/blob/master/UIKit/UIImage2.h