Let’s say you have some photos of cars, houses, etc, and you want to see what they would look like in a different color. Rather than painting the image directly, is there a software package that you can use that will “re-assign” the colors to their equivalent in another color.
Example:
You have a picture of a blue car. You tell the software to change all shades of blue to the equivalent shades of red so that all existing shadows and such are preserved.
Possible?
Easy to do badly, extremely hard to do well.
You got a blue car. Some of the blue parts are in shadow and pratically black. There’s a reflection of a green tree on the left fender. There’s those near white sparklies from sunlight bouncing off various surfaces. The car ain’t all blue in other words. (Assuming the software can already pick out the painted part of the car from everything else so you don’t change the color of the blue sky and such.)
I’ve tried doing this with computer generated images (not pictures) and found it impossible to get right. (I can tell when it’s done in movies as a result of my experience. And they’ve got big time processing power.)
No doubt others will suggest ways of doing it, just be prepared for some really disappointing results.
Brutally difficult. A variety of attributes comprise color. Computers are notoriously weak at color recognition. Oddly, the best software I’ve seen at doing this is one of the less expensive packages out there, Micrografx Picture Publisher. It also has far and away the best masking tool.
ok, let’s see… every possible shade of color on your screen is composed of three levels of the three basic colors which, mixed produce that shade. With a graphics program you have different tools you can use. One is that it allows you to manipulate the “ingredients” so you can make the colors have more or less of oany of the three basic colors. If a picture looks too red or too blue, you can alter the balance so it has less of that particular color and the hue is more natural.
Another thing you can do is exchange one color for another so that what represented blue before will now be red, for example. By combining these and other tools you can do pretty much anything. It just takes time, training and some artistic talent.
You can do them manually, and they can be extremely complex and tricky. You might have to sacrifice hue for saturation, or lightness for contrast, or gamma for midtones. The OP wasn’t asking about something as trivial as changing the color balance of the overall image, but about changing the color of image elements. There is no software that does that well enough in complex images that you could trust its results. Just look at colorized movies, for cryin’ out loud. They use the most expensive technology out there, and you can see horribly egregious misrenderings, especially in the shadows and midtones. That’s why colorization sucks. It looks like something from a coloring book. And when you stop to think that they are colorizing shades of gray, imagine how difficult it is to make elements of an image blue, when the image is, say, hued toward magenta.
And when you say shade, do you mean hue?
D’oh! That leaves me out.
I figured this would be difficult to accomplish. I was just curious. As for colorization of movies/tv shows, have they stopped doing that?
Sadly, no.
I totally disagree, I say it is simple, and the best application out there, and there are 2, one made by Lino-Hell and the other by scitex, both are upper end scanning applications, they make it very simple, at any rate, I say I can do this in photoshop in a snap, and will be back with a link in a moment, it is 4:03 now, give me 10 minnutes to find a image of something like a car, or a apple, or whatever, and start the timers…
OK, so I updated to OSX last night and it tweaked out photoshop, got it reinstalled, and in about 40 sesconds time I managed these 2 images, part of a photo shoot I managed for a catalog. You know the old CMYK catalog thing, anyway, the yellow pain can be bought in the store, no such color as pure CYAN in the the store, so we went with a light blue, which was then pured on my girlfriend as you see. Then, scan them, and I turned the blue one into CYAN as you see here, and I just made the yellow one a few seconds ago. Granted, I was going fast, and if you look close you can see a little blue in the ear on the left, but if I took my time in a half hour, It would be perfect. Notice the background color is not altered, pretty simple masking and color calcualtions in photoshop.
link is here http://newgeo.com/test.jpg
>> The OP wasn’t asking about something as trivial as changing the color balance of the overall image, but about changing the color of image elements
Well, I can’t see why you would be limited to the overall image as graphics programs let you select whatever you want to work on. You can select totally manually or use an “intelligent” selection which will sort of guess the borders for you.
I have done many times the old trick of putting someone’s head on someone else’s (usually naked) body. in B&W this is a pice of cake done in no time but in color it is much more complex because you have to match the skin tones. Still, with some patience it can be done pretty well.
well, it was a simple quick task, anyway, I did not just change the color balance of the whole image, notice the background stayed the same, as did the highlights etc, I used to do this for a living, nothing more than photoshop, a car with reflections and else all over the place, can be done, just takes a half hour or so.
Your girlfriend let you dump a can of paint over her head? That’s gonna change the moment you get married.
Funny, I actually managed to convince 3 of her friends to let me do the same as well. The only tough part was they could not breathe and we needed a full roll of shots that did not look like they were suffocating 
Ohh, note to self- water based not oil
The recolorizing thing is a standard part of the repertoire for any color prepress expert. You can do a lot with masking and selecting color ranges. This recolorizing trick is demonstrated in a lot of Photoshop tips & tricks books, my particular favorite is “Photoshop Artistry” by Barry Haynes and Wendy Crumpler, they have a whole chapter about recolorizing.
Anyway, I used to spend day after day retouching huge color images, even back in the day when a MacIIfx was considered fast. My particular specialty was making blue skies bluer. It is harder than it sounds.
So, Scott & Chas, please tell us how you guys have done it. Dan Margulis explains in one of his articles for Electronic Publishing (sorry, no link - you need to go through a stupid sign-up procedure to get to it) that it was fairly simple for him to reverse a red car to green by going into LAB space in Photoshop and flipping the A & B curves.
Well, in my examples I used photoshop, granted, nothing will ever beat the tools in Scitex’s scanning s-ware of Lino-Color, both about 10 grand or something. But Photoshop 6 has rather intelligent tools for this if you are willing to work a little. If you are looking to do this all day long, look at the pro stuff. generally, and every image is different…
It is critical that the image quality be superb, no internet jpg’s here, digital cameras etc, not to say they will not owrk, but it is to say it will be a whole lot harder. The images from low end scanners and cameras are dirty, take the phot with a SLR camera, using slide film, and pay to have it scanned on a drum scanner. Then, open it up in photoshop, use the color range tool to make a selection, and adjust that selection with color, hue, saturation, levels, every image will be different. You just have to fiddle Note, to change a white car to another color will prove the hardest.
Oh, c’mon.
Nevermind the adulteration of midtones and highlights (looks like you sacrificed saturation for lightness) in your example, but it is a figure that is so easy to mask it’s ridiculous, due to the stark contrast of its defining lines. And every composite element of it is the same hue as the whole. I don’t see why you’d have to do anything more with that example than click it with an automask tool and dump a bucket of paint on it with a merge mode of “color” or “hue”.
Here’s a better challenge. Make this car a bright yellow. Watch out for where it meets the background hills and sky and the guy’s pants. Also, watch out for the shadows under the hood and the separate colors of engine elements. Finally, watch out for the glass color and the colors in its highlights as well as the reflected color on the hubcaps. Note that this image has an overall blue hue. Don’t change that. And don’t change its overall contrast and gamma.
When you’ve finished, I’ll compare the histograms between the original and your effort, and show their particulars here.
there’s a car in that picture? can someone pass a magnifying glass, please? 
Well, a filter would be more use to you than a magnifying glass, but that’s the whole point. When a project is something more than trivial — as in a solid colored bust shape against a dark gray background — colorizing is a heck of a lot more art than it is science, and computers are not a whole lot of help. In fact, if you attempt the given challenge, you will find yourself fighting most of your tools.
Yellow car, after 15 minutes of work:
http://users2.ev1.net/~fpan/yellow_car.jpg
I could’ve done a much better job of masking - and if that was your point, then I failed - but what I’m trying to point out here is that if you work in the LAB space, it’s simple to change colors while preserving the highlights and shadows because you aren’t touching the L (luminosity) channel.
