Should I use UIImage or CGImage in the Swift iOS App?

Question

All the code I can find revolves around loading images directly into visual controls.

However, I have my own caching system (converting a project from another language), and therefore I want as efficiently as possible:

• Download jpg / png images - possibly in a bitmap / cgimage. (it can be either from the file system, or from images downloaded online).
• It is possible to save the image in a compressed / modified png / jpg file
• Link image for visual control

I'm new to the fast and iOS platform, but as far as I can tell, cgimage is as close as it gets? However, there seems to be no way to download an image from the file system using cgimage ... But I found that people are discussing ways, for example, UIImage, so now I doubt my initial impression. Kagmag was the best for my needs.

Answer 1

It's easy to get confused between UIImage , CGImage and CIImage . The difference is as follows:

UIImage: A UIImage object is a high-level way to display image data. You can create images from files, from Quartz image objects, or from the raw image data that you receive. They are immutable and should indicate image properties during initialization. It also means that these image objects are safe to use from any stream. You can usually take an NSData object containing a PNG or JPEG representation JPEG and convert it to a UIImage.

CGImage: A CGImage can only represent bitmaps. Operations in CoreGraphics, such as blending modes and masking, require CGImageRefs . If you need to access and modify the actual bitmap data, you can use CGImage . It can also be converted to NSBitmapImageReps .

CIImage: A CIImage is an immutable object representing an image. This is not an image. It has only image data associated with it. It has all the information needed to create an image. You typically use CIImage objects in conjunction with other Core Image classes such as CIFilter , CIContext , CIColor and CIVector . You can create CIImage objects with data provided from a variety of sources, such as Quartz 2D images, Core Videos, etc. You must use various optimized Core Image GPU filters. They can also be converted to NSBitmapImageReps . It can be based on a processor or GPU.

In conclusion, UIImage is what you are looking for. Causes:

• You can get the image from the device’s memory and assign it to UIImage

• You can get the image from the URL and assign it to UIImage

• You can write UIImage in the desired format to the device’s memory

• You can resize the image assigned to UIImage .

• After you have assigned the UIImage image, you can directly use this instance in the controls. e.g. setting button background, setting as image for UIImageView

Code samples would be added, but all these are the main questions that Stackoverflow has already answered, so it makes no sense. Not to mention adding code, this will make it unnecessarily large.

Summary Credit: Randall Leung

Answer 2

You can easily load an image into a UIImage object ...

 NSData *data = [NSData dataWith...]; UIImage *image = [UIImage imageWithData:data]; 

If you want to show it in a view, you can use UIImageView :

 UIImageView *imageView = [[UIImageView alloc] init]; // or whatever ... imageView.image = image; 

Read more in the UIImage Documentation .

Answer 3

In the documentation at: https://developer.apple.com/documentation/uikit/uiimage

 let uiImage = uiImageView.image let cgImage = uiImage.cgImage