**Table 3:** Estimated mean errors in *UBVRI* gradients for various datasets.
X	Source	$\sigma$
$\Delta _{BV}$	IMP02+	0.010
$\Delta _{BV}$	Gal94	0.017
$\Delta_{VI}$	IMP02+	0.017
$\Delta_{VI}$	Gal94	0.025
$\Delta_{BR}$	IMP02+	0.012
$\Delta_{BR}$	PF++	0.020
$\Delta _{UB}$	IMP02+	0.022
$\Delta _{UB}$	PF++	0.035
$\Delta_{UR}$	IMP02+	0.030
$\Delta_{UR}$	PF++	0.040

(1) Gradient studied X; (2) source of data; (3) estimated mean error $\sigma$ . The source PF++ results from merging the Fal89 and Pal90 data; IMP02+ contains a few OHP images besides those treated in the refered paper.

Source LaTeX | All tables | In the text

	1 Introduction
	2 Collecting the gradients
	3 Properties of colour gradients
	4 Simulated datasets of colour gradients
	5 Concluding summary
	References