libvips operation API by section

arithmetic — pixel arithmetic, trig, log, statistics
colour — colour operators
conversion — convert images in some way: change band format, change header, insert, extract, join
convolution — convolve and correlate images
VipsForeign — load and save images in a variety of formats
freqfilt — fourier transforms and frequency-domin filters
histogram — find, manipulate and apply histograms and lookup tables
draw — drawing operations: flood, paste, line, circle
VipsInterpolate
morphology — morphological operators, rank filters and related image analysis
mosaicing — build image mosaics
create — create images in various ways
resample — resample images in various ways