MOS to PNG Converter

MOS to PNG — Is the PNG Actually Lossless?

Almost every "MOS to PNG" page you will find answers that question with a flat "yes, PNG is lossless". On this converter that answer is only true on one setting, and being straight about which one is the whole point of this page. MOS is the raw file from Leaf medium-format digital backs — the Aptus and Aptus-II line, 22 to 80 megapixels, written as unprocessed sensor data in a TIFF-derived container. Turning that into a PNG means developing the raw first and then choosing how the finished pixels get encoded, and the default encoding is not the lossless one. The short version: pick Highest if you want a true-colour, mathematically lossless PNG; leave it on the default if you want a much smaller file and can accept a quantized palette.

MOS, PNG and JPG Side by Side

What Each Quality Preset Actually Does

The Quality Preset control does something structurally different at the top of the ladder than it does everywhere else:

Palette quantization is how a PNG of a photograph gets meaningfully smaller — it maps millions of colours down to a limited palette and dithers the difference. On a poster or a logo you will not see it. On a medium-format landscape with a smooth sky gradient you may, because a gradient is exactly the content a palette handles worst. That matters more here than on an ordinary photo page: people converting an 80-megapixel Leaf frame are usually chasing maximum fidelity, and the default preset quietly trades some of it away.

When to Pick PNG

• You need an exact-pixel export — a reference frame, a texture, a plate that will be composited or measured rather than just looked at. Set Quality Preset to Highest.
• The image is going into a document, a slide, or a web page where JPEG's block artefacts around hard edges would show.
• You will later add transparency. PNG can carry an alpha channel; the raw itself has none, but you can mask the PNG afterwards without a second lossy round.
• You want a format with no licensing questions attached and universal decoder support.

When to Pick JPG or TIFF Instead

• Sharing, proofing, or publishing a photograph — MOS to JPG produces a far smaller file at fidelity you cannot distinguish at normal viewing sizes. For continuous-tone imagery this is almost always the right call.
• Archiving with the most headroom — MOS to TIFF is the better master format. TIFF carries higher bit depths and richer metadata than PNG, and there is no bit-depth control on this PNG page, so PNG is not the place to chase deep-colour output.
• You need CMYK for press. PNG has no CMYK mode at all. Go to TIFF and separate in your layout application.

How to Convert MOS to PNG

1. Upload Your MOS File: Drag and drop your .mos onto the page or click "+ Add Files". Queue as many frames as you like; they all convert with the same settings.
2. Set the Quality Preset: Under Image Compression, choose Highest for a true-colour lossless PNG. Very High (Recommended) is the default and gives a much smaller quantized file. There is also Specific file size if you need to hit a number rather than a quality level.
3. Adjust Image Resolution, Colors and Compression (Optional): Image resolution starts on Keep original; drop it to a preset if 80 megapixels is more than you need. Colors can reduce the palette explicitly, from 256 down to 2, with an optional dither. Compression level (1-10, default 6) and Compression speed (1-10, default 4) trade encoding time against output size.
4. Convert and Download: Click "Convert" and save the PNG. Files upload over an encrypted connection, are processed on our servers, and are deleted automatically after a few hours. No sign-up, no watermark.

Frequently Asked Questions

So is the PNG lossless or not?

It depends entirely on the Quality Preset. On Highest the converter writes a true-colour PNG and nothing lossy touches it — the encoding is pixel-exact for the developed image. On every other preset, including the Very High default, the PNG is passed through a palette quantizer before you download it, which is a lossy step. The PNG container is always losslessly compressed; what varies is whether the pixels handed to it were reduced first.

Doesn't developing the raw lose something even on Highest?

Yes, and it is worth separating the two losses. "Lossless" on Highest describes the encoding of the finished image. It does not undo raw development: demosaicing, white balance and the tone curve have already been applied and baked in, and the editing latitude that justified shooting medium-format is gone regardless of the preset. Keep the .mos as your master; no PNG is a substitute for it.

Why is my PNG so much larger than a JPG of the same frame?

Because it is not throwing away high-frequency detail the way JPEG's discrete cosine transform does. On an 80-megapixel Leaf frame that difference is dramatic — a lossless PNG of a detailed photograph can be many times the size of a visually equivalent JPEG. If the file is too big to send, either reduce Image resolution, use a lower Quality Preset, or accept that MOS to JPG is the correct format for photographic delivery.

What does the Colors control do, and should I touch it?

It reduces the image to a fixed palette — 256, 128, 64 and so on down to 2 colours — with an optional dither to disguise the banding that reduction creates. It is genuinely useful for graphics, screenshots and flat artwork, where a small palette can shrink a PNG enormously with no visible change. For a medium-format photograph it is the wrong tool: continuous tone is precisely what a small palette destroys. Leave it alone unless you are deliberately going for a posterized look.

Does the PNG have a transparent background?

No. A raw sensor readout has no alpha channel — every photosite recorded light, so there is nothing transparent to carry over. The PNG is fully opaque. PNG can store alpha, which is why it is the right target if your next step is masking the subject out in an editor, but the converter has nothing to mask with on its own.

Can I get a 16-bit PNG out of this?

There is no bit-depth control on this page, so do not plan around one. PNG the format supports 16 bits per channel, but if guaranteed deep-colour output is what you need, MOS to TIFF is the target designed for it — TIFF handles higher bit depths and carries more of the metadata a medium-format workflow cares about.

What do Compression level and Compression speed change?

They affect how hard the encoder works, not what the image looks like at a given preset. Compression level (default 6) governs the DEFLATE effort spent shrinking the finished PNG; higher values take longer and typically save a few percent. Compression speed (default 4) governs the palette quantizer's own speed-versus-quality tradeoff, where lower numbers mean a slower, more careful palette. Neither is worth changing unless you are batching hundreds of frames and care about throughput.

What happens to my MOS file after I upload it?

It is uploaded over an encrypted connection, developed and converted on our servers, and the PNG is returned to you. Both the uploaded raw and the output are deleted automatically after a few hours. No sign-up, no watermark, and your images are never shared or made public. The practical limit on a big Leaf frame is upload size and time rather than anything at the conversion stage.