Pixel anonymization

[Mac Barlow]

Hi all,

I'm working on DICOM file anonymization right now. Tag anonymization practices are relatively straight-forward and we have that working as expected. What I'm wondering is does the DICOM spec have any standards how patient information should be anonymized from the actual image? Or is there any industry standard practice for this? I've been looking and haven't found any specific guidance except either pixelating portions of the image or overwriting portions of the image with black pixels. 

Thanks!

[David Clunie]

There is no "standard" AFAIK as to what to replace the offending region with, if that is what you are asking, just that the stored pixel values needs to be replaced [1].

Nor did we address the replacement values in our task group report [2].

I tried the "pixelation" approach initially for lossless JPEG redaction (e.g. see Fig 4 in [3]) since it was easier than using a single consistent pixel value (due to the need to recompute the JPEG DCT DC coefficient and propagate changes to it), but then I discovered that when the image and text were much larger than 8x8 blocks, the resulting pixelation was sometimes not sufficient to actually obscure the readability of the text, so I changed to a more complex solution that uses a consistent mid-gray value [4].

David

1. https://dicom.nema.org/medical/dicom/current/output/chtml/part15/sect_E.3.html#sect_E.3.1

2. https://pmc.ncbi.nlm.nih.gov/articles/PMC10081345.2/#S64

3. https://pmc.ncbi.nlm.nih.gov/articles/PMC4478853/pdf/JMI-002-016501.pdf

4. https://www.dclunie.com/pixelmed/software/codec/20200328_current/index.html

On Wednesday, October 15, 2025 at 9:32:58 AM UTC-4 Mac Barlow wrote:

... What I'm wondering is does the DICOM spec have any standards how patient information should be anonymized from the actual image? Or is there any industry standard practice for this? I've been looking and haven't found any specific guidance except either pixelating portions of the image or overwriting portions of the image with black pixels.