---
title: previewPhotoFormat
framework: avfoundation
role: symbol
role_heading: Instance Property
path: avfoundation/avcapturephotosettings/previewphotoformat
---

# previewPhotoFormat

A dictionary describing the format for delivery of preview-sized images alongside the main photo.

## Declaration

```swift
var previewPhotoFormat: [String : Any]? { get set }
```

## Mentioned in

Capturing thumbnail and preview images

## Discussion

Discussion By default, this property is nil, specifying that the photo output should return only the main image requested. To also receive a preview-sized image, set this property to a dictionary describing the format for that image, containing the following keys and values: The dictionary must contain the kCVPixelBufferPixelFormatTypeKey key, whose corresponding value must be one of the pixel format types listed in the availablePreviewPhotoPixelFormatTypes array. Optionally, you can also include the kCVPixelBufferWidthKey and kCVPixelBufferHeightKey keys to specify the size of the preview image. (If you specify either width or height, you must specify both.) If the size you specify does not match the aspect ratio of the primary photo, the photo output provides a preview image whose size matches the longer of the two specified dimensions, preserving the original aspect ratio. note: The photo capture system supports both preview and thumbnail images as companions to the full-size primary image in a photo capture. A preview image is intended for immediate display (as seen when taking photos in the iOS Camera app), and as such is sized for full-screen presentation on the current device. A thumbnail image is intended for embedding in the output image file and can be used by other software (such as Quick Look in a file browser) to allow users to quickly review the image without loading the entire image file; the size of thumbnail images may be limited depending on the output file format.

## See Also

### Enabling preview and thumbnail delivery

- [availablePreviewPhotoPixelFormatTypes](avfoundation/avcapturephotosettings/availablepreviewphotopixelformattypes-30d9.md)
- [embeddedThumbnailPhotoFormat](avfoundation/avcapturephotosettings/embeddedthumbnailphotoformat.md)
- [availableRawEmbeddedThumbnailPhotoCodecTypes](avfoundation/avcapturephotosettings/availablerawembeddedthumbnailphotocodectypes.md)
- [rawEmbeddedThumbnailPhotoFormat](avfoundation/avcapturephotosettings/rawembeddedthumbnailphotoformat.md)
- [availableEmbeddedThumbnailPhotoCodecTypes](avfoundation/avcapturephotosettings/availableembeddedthumbnailphotocodectypes.md)