Measuring leaf greenness as a nitrogen signal
Leaf colour carries a nitrogen signal, but only if it is measured against a fixed reference rather than judged by eye. These guides cover the digital indexes that turn an RGB photograph into a comparable greenness value, what DGCI actually measures, and how to compare colour between plants photographed under different light.
Relative Assessment of Greenness with RGB Indices: How to Compare Leaf Colour Between Plants, Treatments and Dates
A long-read on relative greenness assessment from ordinary RGB photographs. Why absolute index values do not travel between cameras, sessions and indexes, what a 37-leaf Petiole Pro experiment shows about DGCI and AGRI agreement (Pearson r = 0.316), and four practical ways — control ratio, z-score, percentile rank and time delta — to turn leaf colour into a comparison you can defend.
29 August 2026
Greenness Measurement Using Digital Indexes for Plant Health Monitoring: A Practical Guide to DGCI, TGI and AGRI in Petiole Pro
A long-read guide to measuring plant greenness with digital colour indexes. Why assessing leaf greenness by eye fails, how DGCI, TGI and AGRI turn a leaf photo into a number, what a 272-leaf Petiole Pro analysis reveals about index agreement and measurement quality, and how to run greenness assessment on the Petiole Pro mobile app and in batch on Petiole Pro Desktop.
14 August 2026
Measuring Leaf Greenness with the Dark Green Colour Index (DGCI): A Field Guide to Petiole Pro and the Greenness Calibrating Plate
A complete guide to measuring leaf greenness and estimating plant nitrogen status with the Dark Green Colour Index (DGCI) in the Petiole Pro app, using the Greenness Calibrating Plate. Covers what DGCI is, how the calibration plate works, step-by-step measurement, best-practice guidelines, and the link between DGCI and SPAD.
1 January 2026Greenness readings need a colour reference to be comparable across photographs: the greenness calibrating plate provides one, and Petiole Pro computes the indexes from it.