Convert DNG to TIFF

This is the difference that runs through the whole page. In a CR2, an NEF, an ARW, an ORF or an RAF, the embedded picture was produced by the camera’s processor at the instant of capture and its size and quality are fixed properties of that body. A DNG might have come from a Leica, a Pentax, a Ricoh, a phone or a drone that writes DNG natively — or it might have been produced by Adobe’s DNG Converter from some other raw file entirely, years after the photograph was taken.

In the Adobe case the preview is whatever the conversion was told to write. The choices offered are Embedded and Sidecar, Medium Size, Full Size and None, and they are per-conversion settings that most people accept the default of and never think about again. A folder of DNGs from the same archive can therefore produce full-resolution TIFFs, half-resolution ones, or a run of failures, depending on decisions made by whoever ran the converter.

The converter looks for every JPEG inside the file and keeps the largest above 640 by 480, refusing anything smaller because handing over a thumbnail is a worse outcome than a clear failure. If a DNG was written with the preview set to None, or with only a small embedded thumbnail, that refusal is what you will see.

It is not a damaged file and the sensor data is intact. The remedies are to re-save the DNG from Adobe’s converter or Lightroom with a full-size preview, which takes seconds per file and is worth doing across an archive once, or to develop the file properly in software that reads the raw data. What will not help is trying again, because there is nothing above the threshold to find.

When Lightroom writes changes back into a DNG, it updates the embedded preview to match. The result is that the picture extracted here can be the adjusted rendering — the exposure lifted, the white balance corrected, the crop applied — rather than the neutral capture.

This is useful when you want it and misleading when you do not. If the DNG came out of somebody’s catalogue, the TIFF you produce may reflect their edits and their crop. If you are working from an archive and need the unedited frame, this route cannot give it to you, because what is stored is the last rendering somebody saved. Convert one file and look at it before assuming which of the two you have.

Four bytes per pixel, no compression, plus about a kilobyte of header. A 20-megapixel drone frame at 5,472 by 3,648 gives 79.8 MB. A 36-megapixel Pentax K-1 file at 7,360 by 4,912 gives 144.6 MB. A 47-megapixel Leica Q2 at 8,368 by 5,584 gives 186.9 MB. A 48-megapixel phone capture at 8,064 by 6,048 gives 195 MB.

If the preview was written at Medium Size rather than Full Size, the numbers fall accordingly and so does the resolution — which is another reason to check the dimensions of the first file rather than the size of the last. A report that needs a picture at 200 mm across the page does not need 8,000 pixels; a print does.

The DNG specification permits 8 to 32 bits per sample; the registry records 16 for it, which is the deepest figure it holds for a raw container — more than the 14 that Canon, Nikon, Sony and Fujifilm write and considerably more than Olympus’s 12. TIFF can hold 16 as well, and this conversion writes eight, because the embedded preview is an eight-bit JPEG and there is nothing deeper to take.

So the one format most likely to be chosen for its archival depth produces, through this route, the shallowest kind of derivative. That is not an argument against the conversion — an eight-bit TIFF is exactly right for placing a picture in a report — but it is an argument against treating the output as anything other than a derivative. The depth is in the DNG and stays there.

DNG is unusual among raw formats in being genuinely open: Adobe published the specification, it was standardised as ISO 12234-2, and it is the reason DNG is recommended by archivists who will not accept a proprietary camera format. TIFF has the same property from a different direction, having been documented and stable since the 1980s.

It is worth being clear that this conversion does not inherit the virtue of either. What it produces is a plain uncompressed baseline TIFF: no compression, one strip, RGB, eight bits per sample, four samples per pixel with the fourth declared as alpha, and no ICC profile. That file will still be readable in fifty years, which is the property people want from TIFF. It contains a rendering rather than the data the rendering came from.

The DNG files most people now hold did not come from a dedicated camera. Drones write them for survey and inspection work, phones write them from computational pipelines, and both produce large numbers of files that end up in reports, claims and planning documents rather than in galleries.

For those the extracted preview is often better than a naive development would be, because the device’s own pipeline did work — noise reduction, lens correction, tone mapping, sometimes multi-frame merging — that a general-purpose raw converter starting from the mosaic data does not reproduce. Converting the preview gives you the picture the device intended. Developing the DNG in unfamiliar software can give you something flatter and noisier, and it is worth comparing the two on one file before choosing a route for a hundred.

The metadata does not survive the decode and re-encode: no camera or phone model, no lens, no exposure settings, no capture time, no GPS coordinate. On drone and phone DNGs that last one is present far more often than on files from a dedicated camera, and the absence is usually welcome.

For survey and inspection work it is also a problem, because the coordinate is frequently the point of the photograph. Read the location out of the DNG and put it in the report, the file name or a sidecar rather than relying on the image file to carry it, and keep the DNGs as the authoritative record of where and when each frame was taken.

If Lightroom or Camera Raw is available and the DNG is in a catalogue, exporting a 16-bit TIFF with a chosen colour profile is better in every measurable way and takes about the same amount of clicking. That is the honest recommendation and this page is not going to argue with it.

What this route is for is the rest of the time: an archive of DNGs whose catalogue is lost, a licence that has expired, a machine you are not allowed to install on, a colleague’s files that arrived without any software, or a hundred drone frames that need to be in a document by the end of the day. In those cases the extracted preview is the picture that exists, and getting it into a TIFF takes seconds.

Everything runs in the browser: the DNG is read from disk by the page, scanned for its embedded preview, decoded and written out as a TIFF. No request carries the image, which the network tab will confirm and a disconnected machine will prove.

Input files are accepted up to 100 MB on the free tier. Most DNGs sit well below that; a 100-megapixel medium-format DNG or a lossless-uncompressed conversion of one can exceed it, and in that case a re-save with Adobe’s lossy DNG option or a direct export from the raw software is the way round. Whole folders can be dropped at once and taken as a ZIP.