---
title: IMAGEIO_PNG_FILTER_SUB
framework: imageio
role: symbol
role_heading: Global Variable
path: imageio/imageio_png_filter_sub
---

# IMAGEIO_PNG_FILTER_SUB

A filter in which each byte is replaced with the difference between it and the corresponding byte to its left.

## Declaration

```swift
var IMAGEIO_PNG_FILTER_SUB: Int32 { get }
```

## See Also

### Pre-Compression Filters

- [kCGImagePropertyPNGCompressionFilter](imageio/kcgimagepropertypngcompressionfilter.md)
- [IMAGEIO_PNG_NO_FILTERS](imageio/imageio_png_no_filters.md)
- [IMAGEIO_PNG_FILTER_NONE](imageio/imageio_png_filter_none.md)
- [IMAGEIO_PNG_FILTER_UP](imageio/imageio_png_filter_up.md)
- [IMAGEIO_PNG_FILTER_AVG](imageio/imageio_png_filter_avg.md)
- [IMAGEIO_PNG_FILTER_PAETH](imageio/imageio_png_filter_paeth.md)