IOS图片展现的两种方法对比
UIImageJPEGRepresentation
Returns the data for the specified image in JPEG format.
NSData * UIImageJPEGRepresentation ( UIImage *image, CGFloat compressionQuality );
Parameters
image
The original image data.
compressionQuality
The quality of the resulting JPEG image, expressed as a value from 0.0 to 1.0. The value 0.0 represents the maximum compression (or lowest quality) while the value 1.0 represents the least compression (or best quality).
Return Value
A data object containing the JPEG data, or nil if there was a problem generating the data. This function may return nil if the image has no data or if the underlying CGImageRef contains data in an unsupported bitmap format.
Discussion
If the image object’s underlying image data has been purged, calling this function forces that data to be reloaded into memory.
UIImagePNGRepresentation
Returns the data for the specified image in PNG format
Declaration
NSData * UIImagePNGRepresentation ( UIImage *image );
Parameters
image
The original image data.
Return Value
A data object containing the PNG data, or nil if there was a problem generating the data. This function may return nil if the image has no data or if the underlying CGImageRef contains data in an unsupported bitmap format.
Discussion
if the image object’s underlying image data has been purged, calling this function forces that data to be reloaded into memory.
