how ios render image

To render images on iOS, especially when dealing with HDR (High Dynamic Range) content, you can utilize several approaches depending on your needs:

1. Using UIImage and SwiftUI: If you are working with a UIImageView or a SwiftUI Image view, iOS provides automatic tone mapping for HDR images. You can create a UIImage using UIImageReader, which supports various HDR file formats, and then display it in a SwiftUI Image view with the allowedDynamicRange modifier to control the dynamic range displayed.

2. Core Image and Metal: For more control or performance needs, you can use Core Image and Metal. This is suitable when you want to interactively change the image. You can apply filters to create an edited CI image and then display it using Metal's MTKView.

3. Tone Mapping: When displaying adaptive HDR images, the approach depends on the edit strategy used. For HDR edit strategies, use the new tonemap headroom filter before display. For ISO HDR files, the new reference white tone mapping operator is used, while adaptive HDR files use a custom tone map function optimized according to the file's gain map.

4. Rendering with Core Graphics: You can render an HDR CG image into an EDR CG bitmap context. This involves creating an extended range CGContext with RGBA half-float pixels and an extended color space, and then rendering the image into the context.

For more detailed information on rendering HDR images, you can refer to the session Use HDR for dynamic image experiences in your app (26:48).