Tagged assay
2 pieces
- · 10 min read
Measure Precision Before You Set a Threshold
Photograph the same sample five times without touching anything and the derived value will differ across the five images. If your decision threshold is narrower than that spread, the decision is a coin toss with a number attached. Precision has to be measured before any cut-off is designed, using the repeatability and reproducibility vocabulary the clinical precision standards already provide, and where precision will not support a decision the honest output is a flag rather than a call.
- · 10 min read
Your Camera Is Lying About Brightness
A camera's response to light is deliberately nonlinear, so the pixel value in a JPEG is not proportional to the light that produced it. Any intensity measurement taken before that encoding is undone is measuring the camera as much as the sample. Fixing it means linearising the response, normalising against an in-frame reference rather than trusting the illumination, and choosing a background subtraction method knowingly, because two standard methods give different corrected values on the same image.