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Revision as of 22:13, 8 April 2011 by KennyTM~ (talk | contribs) (Update info to 4.3.)
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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.


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


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.


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.


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

Equivalent to _UIImageWithName(name).


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

Return the user's lock screen image.


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.

Undocumented C functions


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[1][2], and you can grab a (slightly outdated) list from http://test.saurik.com/winterboard/UIImages.txt.


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).


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[3] and 2010 July[4]

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