Someone on a professional retouching board I belong to, asked a question below. The majority of this post is my response. It is reposted here because the board is for members only and links will not work for non-members.

The posted question was: Does anyone have any tips for the best way to upsize an image for billboard use?

Here is my response:

I do a lot of outdoor campaigns, (or a mix of outdoor and print) so I run into this issue all the time. Worse, many print places that handle large outdoor pieces will establish some crazy guidelines for the artwork they accept. 200 dpi at size for a 14′ x 48′ billboard. Things like that.

In addition almost everything I do is composited, based upon 3-5 photos (sometimes a lot more), so the artwork is a bit more “created out of thin air” than what many retouchers deal with. Most of the outdoor work I do are ads for television, typically 2-3 big heads (or bodies) and some kind of background. Because of this the techniques I use may not work for you particular situation.
(As a curious aside, most television clients refer to outdoor campaigns are Out Of Home, or OOH. Why, I do not know)

So here’s the rules I have slowly discovered over the years:

1) Work at the native resolution of your original images, if at all possible.

This is the most important part of working a campaign of large outdoor pieces. The original artwork will be at whatever resolution it was shot at. This is your starting point, and if it was shot well, and high enough resolution at the start, the only point. For me this means I construct everything at the resolution of my worst photo (or if it is especially bad at some mid point). For the purposes of discussion, we’ll call this selected photo our ALPHA. All images will revolve around its resolution.

In practical terms this means retouching the native images as large as they will come out of RAW, and making sure the work (masks, color corrections, retouching, etc.) will transport well to your composited final files. I’ve found Smart Objects do this well, but not always.

If you doing a campaign (as opposed to a one-off) then build your first composited final piece at whatever resolution your ALPHA photo works to. (if you’re doing a one-off, then assume only one final composition)

This sounds complex, but actually it’s pretty straight forward. I’ll take the initial file (for me this is always a lower resolution comp provided by a design firm), flatten all the layers, and then drag this flattened piece on top of my retouched ALPHA. From that point I simply scale the flattened comp to the correct size so it matches my ALPHA. I find it easy to INVERT the image, and set the OPACITY to 50%, before scaling. Others do other tricks. The important point is to make sure you know EXACTLY what percentages the image was scaled.

For the purpose of discussion, lets say your final composited file needs to be scaled 254.82% to match the size of your ALPHA.

Assuming that the final file is built to mechanical specs in terms of length, width, and bleed (you did build to spec, right?), then all we have to do is change the resolution of the final file to match the ALPHA. Lets say your final file is 150 dpi. Length and width do not matter as we are not going to change them. To scale your 150 dpi file by 254.82% all you have to do is multiply the two numbers, and divide by 100. So 150 x 254.82 = 38223. Take that number and divide by 100 (38223 / 100 = 382.23). So the final resolution of your file will be 382.23 dpi. Set your image size to this (change the dpi ONLY, not anything else), wait for the file to rez up, and then save it off.

Now your ALPHA image should drop right in without resizing.

2) Build your background elements, and any other photos, to the size of your ALPHA.

Once you have them all together make sure you test for accuracy and fidelity. If you have several composited image you may have to tweak them to get them to appear the same level of sharpness. This is why my ALPHA is often my worst file, because everything else will look better.

When the file is done/approved, put it in your mechanical, (Most of my clients dump a flattened TIFF from the final file into an InDesign mechanical. You might do it differently), and you’re good to go.

3) Send the file away to the printers.

On occasion, I’ll get a printer that insists that their specs are the only “correct” ones, and demand the file at “their” resolution. (Never mind that a photo shot at 300 dpi will never be any better than 300 dpi.) To fix a file for them I add a final step. I flatten everything in my final file I can get away with (which is everything that is not type or vector, but excludes any noise layers) and then rez the flattened file up to the specs they require. If there is a noise layer on the top of the composited file, then I rebuild the noise at the final resolution (as opposed to rezzing it up). This will make the printer happy and save you lecturing them on the stupidity of assuming higher resolution is automatically better.
Now all of this came about because there is a lot of confusion out there about resolution and what it means. As I mentioned above, a 300 dpi image is never going to be better than at 300 dpi. Yes you can build it at 600 dpi, or more, but then your going to be doing all kinds of tricks with it to get it to be sharp, and the file is going to take almost twice as long to build.

You clients may or may not know this. They may be under the false assumption that higher rez is always better. Its not. For instance, a blurry shot at 300 dpi is just as bad as a blurry shot at 600 dpi, with the possible exception that one can retouch a 300 dpi file much faster than a 600 dpi one. So uprezing a 300 dpi blurry shot to 600 dpi, just to retouch, is a waste of your time.

There’s another thing. Most outdoor is not printed high rez. I’ve seen billboards printed at a 25 line screen. Do you have any idea how big the dots are at that size? More over, most outdoor is not viewed close up. Most billboards are 20 or 40 feet above ground. No one is going to walk right up to the canvas that high off the ground and say the image is a little soft. All I’m saying is that “sharpness” is a relative term. Chasing a mythical “perfect” point is a waste of time, especially if the original photos were never sharp to begin with. Its better to balance the image as good as you can get it, and let the RIP handle the rest.

Which brings me to my final point. Most outdoor images are sent from your mechanical to a RIP, and then to a printer. The RIP will automatically uprez your file to the proper size for the output device. As long as the type elements are still sharp (read still in postscript, hence building the mechanical and all possible type in InDesign) then the final image should hold up well. It makes no difference if YOU uprez up your file, or if the RIP uprezzes it, with the possible exception that the RIP will probably do a better job at keeping the file consistent.

Back in December of 2011, someone on a professional retouchers board asked for opinions on the future of retouching. Since the board is a for members only (links will not work for non-members), I’ve duplicated my response here.

A few things here. I see a growing trend in retouching, and I don’t think it has hit its peak yet. Alas, the vast majority of this growth is happening at the low and mid ranges of the work. At a hunch I’d say that for every piece of art one of us professionals crank out, 10 pieces of mid range art are done, and 100 pieces of crappy art are done.

This reflects a similar trend I see which is the growing knowledge of how to retouch. More and more people are starting out in photoshop, and doing their first composites, color corrections, etc. Again, like the statistics I guessed at above, I would bet over 90% of these newbies never get past the “amateur” phase. Probably 8-10% will develop their ability into the intermediate range, and only a small few will reach the rank of “pro”.

Both of these trends are made possible by the growing understanding or photo retouching in the general population. Most people know that one can do something interesting in Photoshop (although most would be fuzzy about the specifics). One can now use the verb “Photoshopped” or ‘shopped” or photochopped” and most English speaking people will know exactly what you mean.

All of these things are a boon for us. The largest hurdle in getting a new client to understand the value of what we do is to getting them to understand what we CAN do. Alas, like the numbers above, most of this new work will start out in the cheap range. They will either hire an amateur, or they will pass on the job to an employee. Most of these new potential photoshop clients will not develop the budgets, or the understanding, to hire a professional retoucher.

Still, I would bet professional retouching holds a consistent 5%-10% of the market share in terms of numbers of items retouched, and probably 50% or more of the market in terms of money earned.

At some point, and no I do not know when, I think the demand for retouching will start to decline, or at least flatten off. Yet numbers of people who gain the knowledge or retouching will probably not peak for quite some time after that. If this happens, then expect to see even the professional range of retouching slowly get saturated with too many retouchers. This will drive down prices, and quality. Neither of which is in our best interest. It will also start to place a greater value on certification of professional ability. Expect to see various ad hoc retouching groups get together and “certify” their professional ability, usually though some sort of professional organization.

All of that is about the work, but that is not all that is changing. The tools we use to retouch are also subject to change.

Sometime in the early 90s, digital retouching started to compete and then overcome traditional retouching. This was a revolutionary change, and not always for the better, as it left a lot of retouching professionals behind. It also made for a lot more work. The good news for us is that I do not see another revolution to our business coming soon. At least not on that scale. We will see some changes, but they will happen at a more moderate rate, and if we are careful, most of us should be able to transition with them successfully.

Our primary tool right now is Photoshop, and the program is definitely starting to get into  the bloated range of software. In many ways this is good for us. Without any serious competition, Photoshop will remain largely consistent, which means we can change with it. Adobe is more interested in finding stupid crap to put in it, so they can justify their goal, which is to get you to buy a new version of the software at least once a year. This is how most software companies make their money. The good news is this allows them to evolve the product slowly, the bad news is this tends to make the product more bloated with junk. I don’t expect to see any large changes to photoshop soon because I don’t expect to see any serious competition to it. Adobe has done an excellent job of watching the little guys, and adopting their better ideas. This is a good model for them, so expect to see more of it in the future.

Where I do expect to see change is in the interface with computers. I think iOS (like on the iPad, iPhone, or Android devices) represent the future of ALL computer work. Couple this trend with the higher resolution touch-screen monitors now coming out, and you start to see a glimmer of what our work will be like in the future. 10 years from now I doubt we will be using a keyboard on our computers. I think the majority of our work will be done with our hands right on the screen, and likely using a stylus of some type. If this is true, then expect to see our work areas go back to something like drafting tables, with large surface areas to rest our hands/arms while we work on the big screen. This more “hands on” approach will not be for everybody, but I expect it to eventually dominate because it more accurately reflects how people actually work. IN that sense, the work of retouching will more closely resemble the other arts, like drawing and painting.

Beyond that, expect to see computers getting faster and faster (over 7 times as fast at they are now in 10 years), files getting bigger and bigger, and the process of retouching being more and more automated. A lot of the easy and intermediate retouching work can be automated, especially with faster/smarter computers. The high end work will probably NOT be. I say this because 1) high end work is a highly complex task (in other words, its art), and 2) because there is not enough money in it to make it worth the investment.

Anyway, that’s some of what I see coming down the pipe. As you can guess, I’ve done a bit of thinking about this. I happen to read and write a lot of sic-fi, so projecting future trends is a bit of a hobby.