Each and every superhero has their own distict costume but when it comes to the movies these are usually changed to suit a wider audience. Is this needed or do studios do it just to make films more realistic?
There is no doubt that some costumes would be almost impossible to adapt to screen. A giant purple planet eater would take you out of the film, but in a film with silver surfers it would be okay as long as it was toned down. Making it a giant cloud small refernces to the helmet is not excusable. Hell anyone on this site could of come up something better than that. X men costumes are also in this catergory, many people didn't like the reimagined costume but to be honest having each x man wearing such diffrent attire like yellow spandex with a cowl might have looked silly on screen,(though they could of referenced in XMOW).

However sometimes these changes are neccesary. With different incarnations of a character you have to be influenced by the comics yet still have the costume difinitive to you. Many films have done this brilliantly. In Captain America his costume may still be an america flag but it is toned down to fit with its WW2 setting yet still looking ahead of its time. In the Nolan Batman films the costume was changed to an all black colour scheme which wouldn't work in comics yet it fits perfectly in the darker, more gritty films.
Furthermore there are even costumes that were taken straight out of the comicbooks. In the original superman films the costume was an exact replica from the comicbooks yet still fit into the movies, Sam Raimi's spider-man films also did this. Why has it worked for these films and not others, is it because they are worse films or is it because these films aren't trying to be real and just a faithful adaption. I'm going with the latter.
Personally I think that it is okay to change costumes in movies but only when it is necessary in terms of tone and story, why change the material if it is darn near perfect. But in thinking of the future I can't help but be reminded of Green Lanterns CGI costume and how other studios may try it out with there characters. A little CGI is okay but only to improve on an already made costume.
Thanks for reading, comments are much appreciated!