A mural is any piece of artwork painted or applied directly on a wall, ceiling or other large permanent surface. This form of art was used from upper paleolithic time to modern time.
King like Tipu Sultan continued to encourage local traditions and had the walls of his palace at Seringapatam covered with mural paintings done by the local artists. One of these mural paintings celebrates the victory of Tipu and Haidar Ali in the Battle of Polilur (1780) in which they defeated the British troops.

Raja Ravi Varma's mythological paintings became very popular. Responding to this popularity, Ravi Varma decided to set-up a picture production team and printing press on the outskirts of Bombay. Colour prints of his religious paintings were mass produced. These prints were affordable, so the poor could also buy these cheap prints.

By the mid-19th century, many photographers from Europe came to India and began travelling.
They took different types of pictures such as:
(i) Some took photographs of imperial officials, presenting them as figures of authority and power.
(ii) Others took pictures of ruined buildings and picturesque landscapes.
(iii) Others recorded moments of British military triumph.
(iv) There were also some who recorded the cultural diversity of India in ways that tried to show how India was a primitive country.

The rich and powerful people, both British and Indian, wanted to see themselves on canvas.
Indian tradition of portrait painting was in form of miniature (very small detailed painting) at that time.
A stream of European portrait painters came to India in the 18th century. They made portraits that were life-size images that looked lifelike and real.

Local Indian painters produced a vast number of images of local plants and animals, historical buildings and monuments, festivals and processions, trades and crafts, castes and communities. These pictures were eagerly collected by the East India Company officials as they wanted images through which they could understand and remember India. These are known as Company Paintings.

By the late 19th century, mechanical printing presses were set-up in different parts of India which allowed prints to be produced in even larger numbers.
Popular pictures of Hindu deities printed in large numbers, so that even the poor could buy them. With the spread of nationalism, popular prints of Bharat Mata or nationalist heroes of the freedom movement became popular.
Ravi Varma set-up printing press where his religious paintings were mass produced. These prints carried nationalist messages and influenced large number of people and created nationalistic fervour.

I think some artists wanted to develop a national style of art due to following reasons:
(i) Towards the end of the 19th century, a stronger convention was established between art and nationalism.
(ii) There was a huge popular appeal of mythological stories paintings, related with different scenes from the Mahabharata and the Ramayana.
(iii) Some Bengali painters and artists felt that a genuine Indian style of painting had to draw inspiration from non-western art and tradition and they tried to capture the spiritual essence of the East.
(iv) There were some Indian artists and painters who felt that artists had to explore real life instead of illustrating ancient books and look for inspiration from living folk art and tribal designs of different regions of India rather than ancient or medieval art forms.

The scroll painters and potters came to Kalighat and settled there because at that time Calcutta was expanding as a commercial and administrative centre. Calcutta appeared as a place of opportunity where people came to make a new livelihood for them.
Village artists also came and settled here in the hope of new patrons and buyers. They began to paint new themes because values, tastes, social norms and customs were undergoing fast changes after the 1840s. Kalighat painters responded to these changes and produced paintings on social and political themes.

Many of the Indian nawabs who lost their power and status to the British began commissioning imposing oil portraits by the European painters. Their power was undermined by the British officials.
Some nawabs reacted against this interference, others accepted the political and cultural superiority of the British.
Some nawabs hoped to socialise with the British and adopted their styles and tastes. Some nawabs like Muhammad Ali Khan of Arcot even gifted portraits to the King of England and the Directors of the East India Company.

During the colonial era, Western influences started to make an impact on Indian art. Some artists developed a style that used western ideas of composition, perspective and realism to illustrate Indian themes.
The Bengal School of Art was an influential style of art that flourished in India during the British Raj in the early 20th century.
This school arose as an avant-garde and supporter of nationalist movement reacting against artists like Raja Ravi Varma.
Abanindranath Tagore and his disciples and followers believed that the style of Raja Ravi Varma was unsuitable for depicting the nation's ancient myths and legends.