LearnAI measured-image release: onion-epidermis-v1
Title: Cells from a red onion epidermal peel
Creator: Adrian J. Hunter
Date: 29 June 2014
Source: creator's own work on Wikimedia Commons
Source record (reviewed 25 October 2026):
https://commons.wikimedia.org/w/index.php?title=File:Cells_from_a_red_onion_epidermal_peel.tif&oldid=1222730780
License: Creative Commons Attribution-ShareAlike 3.0 Unported
https://creativecommons.org/licenses/by-sa/3.0/
Credit the creator and source, link the license, and indicate modifications.
The local image and annotated image presentation are offered under CC BY-SA 3.0.
No endorsement by the creator or Wikimedia is implied.

Source description identifies pigmented Allium cepa epidermal cells, an Olympus CX31 microscope, 100x magnification, a 99 ms exposure, and a FULL scale bar of 200 micrometres.
Do not treat one alternating bar segment as the full 200-micrometre reference.
Magnification alone is not used for calibration.

Original TIFF (unaltered bytes):
https://upload.wikimedia.org/wikipedia/commons/1/1a/Cells_from_a_red_onion_epidermal_peel.tif
Local: onion-epidermis-original.tif
998 x 698 pixels; 2,092,830 bytes.
SHA-1: ef9e61ca7d4287a99c95712b531c04a5197506df
This SHA-1 matches the repository's recorded original-file checksum.
SHA-256: 0c80d10ba5e3a7c9ad9266a439116b8fa7bb75753c332011d60c5a4912074a39

Browser image (unaltered Wikimedia preview bytes):
https://thumb.wikimedia.org/wikipedia/commons/thumb/1/1a/Cells_from_a_red_onion_epidermal_peel.tif/lossy-page1-960px-Cells_from_a_red_onion_epidermal_peel.tif.jpg
Local: onion-epidermis-v1.jpg
960 x 671 pixels; 65,258 bytes.
SHA-256: a1162572624209b0d914eb817795a028977d0db377e7c01d3f047279bd24d234
Wikimedia resized/transcoded the original to this lossy JPEG preview. LearnAI does not crop, recolor, sharpen or generate specimen pixels. Browser display may scale the whole image uniformly; coordinate calculations stay in the frozen preview's pixel space. Measurement overlays are separate SVG elements and can be hidden.

Calibration and analysis:
The source's full bar is taken as nominally 200 micrometres. In the local preview, an initial manual span estimate uses x=586 to x=930 (344 pixels) near y=589. This is a learner-adjustable endpoint estimate, not a supplied instrument calibration certificate. The bracket center is fixed at x=758. Adjust the span by inspecting the actual full bar.
Initial candidate cell chord: (275,183) to (450,183). These are teaching starting coordinates, not expert-validated boundaries or ground-truth cell dimensions.
Coordinates have origin at upper left, x rightward and y downward.
Line length uses Euclidean pixel distance; physical length = pixel length x 200 / full-bar pixel span.
Position-tolerance bounds allow each of the two line endpoints and each of the two bar endpoints to vary within an equal pixel radius. They exclude unknown source calibration, preparation, optical and compression effects; they are not confidence intervals.
The exercise does not identify nuclei, measure depth or cell volume, infer pigment concentration, or establish typical cell size. One photographed field does not establish biological replication.
Changing this asset or its calibration convention requires a new release identity or an explicit migration of recorded measurements.