Can Crank be considered graphic novel?

Technically, yes. The term 'graphic novel' refers to bound volumes of sequential art that tells a story, a description that manga fits.

A graphic novel is a novel, a work of usually adult fiction , written and drawn in comic book form. It was a fairly common practice for some newspapers to serialize popular if mild (not off-color)...

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It really depends on the graphic novel itself and what the person colouring it is comfortable in.For the most part a lot the books out there are coloured by computer using Adobe Photoshop or similar...

Maus : A Survivor's Tale is a graphic novel by Art Spiegleman .