Having been an artist who's worked under the same writer for two years, I feel the writer/artist relationship is best represented with a Venn Diagram.
Writer:
-Plot
-Dialogue
-Character Roles
Artist:
-Lines
-Colors
-Shading
Writer AND Artist:
-Setting
-Tone
-Character Design
-Characterization
-Visual Communication
-Layout, Pacing
On his own, my writer determines the plot, general direction, and dialogue of a strip. On my own, I draw pretty little lines which our colorist colors and shades afterwards. The real MEAT is when we work together, however. How the world feels, how the characters actually
act and communicate through visual cues, how the script is laid out across the panels... it's most certainly a combined effort. Check our latest strip, for instance:
Image: http://lvl30psy.thecomicseries.com/images/comics/63/ab842d408887a8d09e969797442a44e0629417591.png
My writer wrote this script.
I originally came up with the idea of using simplified "chibi head bars" to fit in more dialogue (or repetitive dialogue, in this case) many months ago.
My writer suggested I use them for this strip to lessen my workload.
I chose to exaggerate the characters' expressions in Panels 5 & 6 to better communicate their emotions.
My writer then changed the dialogue in Panel 6 at the last moment to create a better punchline.
Point is, my writer could just as easily have specified to exaggerate the characters' expressions, but he didn't -- I did -- although he very well could have. He did, however, specify them to be angry and worried, but if he didn't do that, I could have added that in anyway. Being a visual medium, comics create lots of overlapping responsibilities in the process.
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Have a laugh and hunt for cameos every Sunday.