An image forming method comprising: extracting one or more graphical primitives included in print data; forming an image by arranging the one or more graphical primitives according to a determination of whether the extracted graphical primitives are disposed within a predetermined distance of each other or not, wherein the forming the image comprises: detecting a bounding area of the extracted graphical primitives; and when the detected bounding areas are overlapped with each other, combining the graphical primitives corresponding to the bounding areas overlapping each other into the image; converting the formed image into a sketch image, wherein the converting comprises: rasterizing the image which is represented by a group of the one or more graphical primitives into a bitmap; and converting the bitmap into the sketch image, and the converting the bitmap into the sketch image comprises: converting the bitmap into a monochrome image; detecting an edge of the monochrome image and generating a mask; and generating the sketch image by multiplying the bitmap image with the mask; modifying the print data by replacing it with the sketch image and a portion of the graphical primitives constituting the sketch image; and draft-printing using the modified print data. extracting one or more graphical primitives included in print data; forming an image by arranging the one or more graphical primitives according to a determination of whether the extracted graphical primitives are disposed within a predetermined distance of each other or not, wherein the forming the image comprises: detecting a bounding area of the extracted graphical primitives; and when the detected bounding areas are overlapped with each other, combining the graphical primitives corresponding to the bounding areas overlapping each other into the image; converting the formed image into a sketch image, wherein the converting comprises: rasterizing the image which is represented by a group of the one or more graphical primitives into a bitmap; and converting the bitmap into the sketch image, and the converting the bitmap into the sketch image comprises: converting the bitmap into a monochrome image; detecting an edge of the monochrome image and generating a mask; and generating the sketch image by multiplying the bitmap image with the mask; modifying the print data by replacing it with the sketch image and a portion of the graphical primitives constituting the sketch image; and draft-printing using the modified print data. detecting a bounding area of the extracted graphical primitives; and when the detected bounding areas are overlapped with each other, combining the graphical primitives corresponding to the bounding areas overlapping each other into the image; converting the formed image into a sketch image, wherein the converting comprises: rasterizing the image which is represented by a group of the one or more graphical primitives into a bitmap; and converting the bitmap into the sketch image, and the converting the bitmap into the sketch image comprises: converting the bitmap into a monochrome image; detecting an edge of the monochrome image and generating a mask; and generating the sketch image by multiplying the bitmap image with the mask; rasterizing the image which is represented by a group of the one or more graphical primitives into a bitmap; and converting the bitmap into the sketch image, and the converting the bitmap into the sketch image comprises: converting the bitmap into a monochrome image; detecting an edge of the monochrome image and generating a mask; and generating the sketch image by multiplying the bitmap image with the mask; converting the bitmap into a monochrome image; detecting an edge of the monochrome image and generating a mask; and generating the sketch image by multiplying the bitmap image with the mask; modifying the print data by replacing it with the sketch image and a portion of the graphical primitives constituting the sketch image; and draft-printing using the modified print data.