Hi all....I am a bit of newbie but I have tried to do my homework on this one before asking and I just can't seem to get it right.
Some of the newer projectors can compensate for projection on a colored wall. I have a series of images I need to show on a medium dark wall with a green cast to it and the projector does not have this feature. I had thought I could figure out how to edit the image to enhance the right colors and get a fair balance of color (I don't expect it to be perfect, just better than it is right now). I looked at using "convert -recolor" and an appropriate matrix. My thought was to take a color sample of the wall and get the RGB value for the color. In this case it looks like 114 - 119 - 90. So, I figured I just needed to increase the R and B channels proportionally to the G channel and I should get something that looks OK....but I don't. There is still a significant cast to the picture and some very wrong colors (e.g. violet appearing redish-orange). My model was kind of simple. I figure the wall represented surface of a particular color. If I shine a light on a solid red wall, for example, I would only get red back. Assuming that the wall was perfectly red from an RGB standpoint, it would reflect red perfectly (I will use (1,1,1) to represent (255,255,255) in an RGB format). (1,0,0) -> incident light | | (1,0,0) -> reflected light | / ----------------------------- (1,0,0) -> wall color If I now shine a perfectly green light on the wall, it should appear black: (0,1,0) -> incident light | | (0,0,0) -> reflected light | / ----------------------------- (1,0,0) -> wall color So now shine a white light against a greyish wall with a slightly dominant green and it will reflect the same color: (1,1,1) -> incident light | | (0.3,0.4,0.35) -> reflected light | / ----------------------------- (0.3,0.4,0.35) -> wall color My thought was if I enhance the incoming color slightly to compensate for the different level of the various colors. I expect the picture to be darker because I can't really completely overcome the grey in the wall, but I would hope to get reflected light that was grey not with a green cast to it....the problem is I can't seem to figure out how to proportionally adjust the color levels in the incoming light to compensate adequately for the wall color. For the example above, I pick green as the reference and adjust the other two colors to match it....this gives me a matrix like this: 1.3333 0 0 0 1 0 0 0 1.1428 This in theory should give me a reflected light (0.4,0.4,0.4) if my simple model is correct. I can't test this until Thursday unfortunately so I am not 100% sure I am doing this correctly. My concern is that I am not accounting for a non-linear scaling that would be necessary to make this work right. Does anyone know how I could convert images for projecting onto a colored wall? It has now become somewhat of a crusade for me to figure this out.... Dave _______________________________________________ Magick-users mailing list [email protected] http://studio.imagemagick.org/mailman/listinfo/magick-users
