在iOS中以编程方式压缩PNG图像

Question

I need to send to server png images with 300DPI and exactly 1275x1875pixels in size. Because by default UIKit will create image with 72DPI, I need to set scale factor to 300/72 in UIKit function UIGraphicsBeginImageContextWithOptions to be able to get 300DPI image, and after this I'm using UIImagePNGRepresentation function to get NSData of image and write it in file. For now I can get desired image size and DPI (have checked in photoshop), but it becomes almost 5mb. Is there any way to reduce PNG image size in iOS?

Thanks in advance!

Answer 1

If you need compression, why not send those images as JPEG instead?

NSData * UIImageJPEGRepresentation ( UIImage *image, CGFloat compressionQuality );

Set compressionQuality to 0f for highest compression, 1f for lowest. Convert back to PNG when you need a PNG.