<!--
{
  "availability" : [
    "iOS: 9.0.0 -",
    "iPadOS: 9.0.0 -",
    "macCatalyst: 13.1.0 -",
    "macOS: 10.11.0 -",
    "tvOS: 9.0.0 -",
    "visionOS: 1.0.0 -",
    "watchOS: 2.0.0 -"
  ],
  "documentType" : "symbol",
  "framework" : "ImageIO",
  "identifier" : "/documentation/ImageIO/kCGImageSourceSubsampleFactor",
  "metadataVersion" : "0.1.0",
  "role" : "Global Variable",
  "symbol" : {
    "kind" : "Global Variable",
    "modules" : [
      "Image I/O"
    ],
    "preciseIdentifier" : "c:@kCGImageSourceSubsampleFactor"
  },
  "title" : "kCGImageSourceSubsampleFactor"
}
-->

# kCGImageSourceSubsampleFactor

The factor by which to scale down any returned images.

```
let kCGImageSourceSubsampleFactor: CFString
```

## Discussion

When you specify this key, the image source scales down the image data by the specified numerical factor. The value of this key must be a <doc://com.apple.documentation/documentation/CoreFoundation/CFNumber> containing the integer value 2, 4, or 8. If the image doesn’t support the specified scale factor, the image source provides a larger or full-size normal image.

Image sources support this option only for JPEG, HEIF, TIFF, and PNG images.

---

Copyright &copy; 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)