Recently, I did some graphics programming. The task I gave myself was to highlight a JPEG by drawing a box around an interesting part of the image. The puzzle was which color to make the box so that it would stand out.
\n
\nMy first color choice was black, but if the image is mostly black, the box wouldn’t show up. The same logic follows for white and other colors as well.<\/p>\n
For example, I tried bright green, but the results were ugly. I tried a box made of two rectangles, one white and one black, but on a larger image canvas, this box wasn’t that obvious. So my solution was instead to use existing pixels to draw the box, making each pixel brighter by 10 percent.<\/p>\n
In a JPEG image, pixels are stored as three values: red, green, and blue. Each value ranges from 0 to 255, which in C fits into an unsigned char<\/em> variable. Ten percent of 255 is 25, so for each color value in the pixel, I would add 25 to increase brightness. (I’m sure that nerdy graphics programmers would claim that this method doesn’t increase brightness but blah-blah-blah<\/em>. Whatever. Work with me here.)<\/p>\n The problem, of course, is that you cannot increase a pixel’s color element value beyond 255; if you add 25 to a pixel value of 250, for example, you get 275. This result is an overflow. In C, adding 25 to an unsigned char<\/em> value of 250 yields 19, not 275; the value wraps within the confines of the unsigned char<\/em>.<\/p>\n This month’s Exercise is to take a line of pixels stored in a structure and increase each value by 10 percent without going over 255. Use the code below as a skeleton to craft your solution:<\/p>\n Click here<\/a> to view my solution, but please work on this puzzle yourself before you see what I’ve done.<\/p>\n","protected":false},"excerpt":{"rendered":" You can’t fill up a cup beyond its brim. Continue reading \r\n#include <stdio.h>\r\n\r\nint main()\r\n{\r\n struct color {\r\n unsigned char r;\r\n unsigned char g;\r\n unsigned char b;\r\n };\r\n struct color pixels[15] = {\r\n {247, 63, 29},{251,100, 33},{250,146, 38},\r\n {252,196, 46},{252,223, 51},{250,225, 56},\r\n {196,225, 53},{134,252, 49},{ 66,221, 48},\r\n { 63,251,158},{ 60,253,233},{ 54,236,250},\r\n { 35,181,249},{ 0,104,249},{ 0, 54,251}\r\n };\r\n\r\n\/* your solution here *\/<\/span>\r\n\r\n return(0);\r\n}<\/pre>\n