What changes in the file
- Compression model
- HEIC is lossy and PNG's own compression is lossless, so the conversion adds no new compression artefacts. It is not loss-free end to end, though, an 8-bit HEIC comes through pixel-for-pixel, while a 10-bit one is quantised to 8 bits (see below). Neither case can undo the loss the camera baked in.
- File size, upward
- Expect the PNG to be much larger than the HEIC. No published corpus fixes the ratio and this site does not invent one. It depends heavily on the photograph. PNG's DEFLATE compression is built for flat colour and sharp edges, and photographic noise is close to worst case for it, so the exact ratio depends heavily on the photograph.
- Alpha channel
- PNG supports real per-pixel transparency, but a camera HEIC has none to carry over and PixelFerry does not add one. Measured, a photographic HEIC decodes to three channels and the PNG comes out with three. If you need an alpha channel for a compositing step, it has to come from the source.
- Bit depth handling
- PixelFerry writes 8-bit PNG. A 10-bit HEIC is quantised on the way through, exactly as it would be for JPEG, so PNG does not preserve the extra tonal precision an iPhone captured.
PNG is the “stop losing quality here” format
Every time a lossy image is decoded, edited and re-saved, it loses a little more. That is generational loss, and it is why a meme that has been through fifteen phones looks the way it does.
Converting HEIC to PNG draws a line under that: from the PNG onward, a save that stays lossless reproduces the pixels exactly. Re-export it as a JPEG and you are back to generational loss, the PNG protects you from the compounding, not from the next lossy encode.
Two things it does not do. It cannot undo the loss the HEIC already baked in, and it does not carry more than 8 bits per channel through, because PixelFerry writes 8-bit PNG, so a 10-bit capture is quantised once, at this step.
What it is not is a way to make the image better. A lossless container around a lossy image is still a lossy image. If you are converting purely so the file opens somewhere, JPG is the smaller and more sensible target.
The size problem, concretely
PNG compresses with DEFLATE, which finds runs and repeated patterns. Screenshots, logos and flat illustration compress beautifully. Photographs barely compress at all, because adjacent pixels differ by small random amounts from sensor noise.
A 12-megapixel photo is roughly 12 million pixels × 3 bytes before compression, and DEFLATE has little repetition to exploit in photographic noise. A PNG of photographic content can be much larger than the HEIC it came from, and that is normal rather than a sign anything went wrong. No published corpus fixes the ratio. It depends heavily on the image.
If the destination can read them, WebP in lossless mode reproduces that same 8-bit result exactly, and is usually smaller. See that page for Google’s published figures and their baselines.
Running a batch
Drop the HEICs (or the whole folder) onto the window, set the output format to
PNG, and pick a destination. There is no quality slider for PNG, because there
is no quality decision to make; PixelFerry writes at maximum compression
(compressionLevel: 9), which is slower to encode and smaller on disk, and
identical in output.
Resize is where this conversion usually earns its keep. Converting a 12-megapixel HEIC to a full-resolution PNG and then scaling it down in another tool means writing a very large intermediate to disk for no reason. Setting the target width in the same pass skips that entirely.
The queue mixes freely. HEICs from a phone, RAW files from a camera and PSDs from a designer can all sit in the same batch and come out as PNGs with one set of rules applied to all of them, at an exact width, into a folder you choose, with a per-file result. The Finder Quick Action converts a selection too, but its sizing is four named presets, it has no quality control, and it writes beside the originals.
When people do this
- Handing a photo to a designer or a compositing step where any further generational loss is unacceptable.
- Feeding images into a tool that will not read HEIC and where you would rather not introduce a second lossy pass before editing.
- Producing a screenshot-quality asset from an iPhone capture that will be annotated and re-saved several times.
What macOS already does
The Finder Convert Image Quick Action.Right-clicking a selection in Finder and choosing Convert Image offers PNG alongside JPEG and HEIF, and it will happily do a large selection in place. For a handful of files it is usually the simplest built-in route.
Where it stops being enough:You need to resize in the same pass, want the results in a separate folder rather than beside the originals, or need to know which specific file failed in a batch of hundreds.
Limitations worth knowing first
- The output is genuinely large. Converting a folder of iPhone photos to PNG needs meaningfully more disk than the originals did, so check the destination has room before starting a big batch.
- PNG is lossless but not magic. It cannot recover detail the HEIC encoder already discarded.
- PixelFerry writes 8-bit PNG, so this is not a route for preserving 10-bit HDR stills.
PixelFerry requires macOS 14 (Sonoma) or later on Apple silicon and Intel. Conversion runs entirely on your Mac. No file, and no part of one, is uploaded anywhere.