Flattening background-subtracted images (Fig. 2). Shown are the standard deviations of small-scale fluctuations in (upper row), median-filtered scaling (flattening) images (middle row), and flattened detection images (bottom row) at selected Herschel wavelengths. In panel b, thin ring-like structures reflect the off-center temperature peaks in starless cores illuminated by the interstellar radiation field. The maximum sizes X_λ of 25, 100, and 100′′ are the same as those used for background derivation.