Film forming method, image forming method, film, and ink composition

An image forming method comprising:

• forming a white image on a substrate by applying an ink composition comprising titanium oxide particles having an average particle size of 10 nm or more and 100 nm or less and an aggregating agent that aggregates the titanium oxide particles,
• wherein the aggregating agent is at least one of an inorganic polyvalent metal salt which is soluble in water and an organic acid,
• the image includes first regions, second regions, and third regions, the first regions, the second regions, and the third regions being defined by a refractive index and a region size and being present in a mixed manner in a cross section parallel to a thickness direction of the substrate,
• the first regions and the second regions have a refractive index at least 0.4 higher than the third regions,
• the second regions are formed of the titanium oxide particles that have not been aggregated by the aggregating agent,
• the first regions are formed of the titanium oxide particles that have been aggregated by the aggregating agent, the first regions having an equivalent circular diameter of 250 nm or more,
• the third regions have an equivalent circular diameter of more than 100 nm.