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Question

Up-scaling an image, an idiots guide please.

Forum|Forum|8 years ago
June 1, 2017
4 replies
1138 views

So, I have been given a task at work, for a fair sum of money, to deliver some pictures for our walls.
Thing is, my boss wants some of them to be 60cm x 220cm, as he has some of these already, but they are out-dated.
The previous photographer took 5 or 6 portrait images and merged them to one, but made a complete mess of it when stitching them together. There are telephone lines stopping in mid air, huge differences in color, spots and just bad editing work.
Seeing this I decided not to do the same mistake, and just took one photo and cropped the hell out of it. Rookie mistake no. 1 for me...
When I delivered my images to the print guy I saw why the previous photographer had done what he did. My images looked like crap when blown up to those dimensions. My regular 3:4 was just fine, but the 60x220 looked awful.
Some of it I blame Googles NIK filters, as I used some of the contrast features there, and it left noise looking like little worms when up-scaled. Just horrible.
I showed my boss the problem, and he said "Just fix it. I want those pictures."
Easy step would be to go back and shoot it again, doing portrait style pictures and stitching them together, but I can't as there is a huge construction site blocking the scenery now...
So I now need to up-scale the images, if possible. I have heard that there is a 10% rule when up-scaling, as doing just one big gulp will ruin the result. Something about some algorithms or something.
Can anybody help me in this process? And if you have, suggestions on how to prepair for a large scale print?
And please dumb it down a bit in easy steps, as English is not my native language, and I'm not THAT good in PS, when it comes to all the techy stuff.

To give an idea, I'll add a pic to let you see what I mean and need.

Picture is taken with a Canon 7D mkII
Original resolution is 5472x 3648 straight out of the camera. I need the cropped area to fill the space of a 60cm x 220cm canvas...
Am I doomed?

Thanks for all and any help.

This topic has been closed for replies.

T

theStigNorwayAuthor

Participating Frequently

This will be in a narrow corridor, so I'm probably screwed then, as I've said before, I can't reshoot it. The scenery does'nt exist like this anymore :-(

D Fosse

Community Expert

I still think it'll work. Try to print out a small section at actual size and check.

As I said, people always overestimate ppi requirements.

What is entirely certain, is that upsampling won't do any good. You'll just get the worm-like structure you mentioned (and that's actually a very good description of it).

Use the ACR filter to sharpen the edges, taking care to avoid halos. This is achieved by using a low "detail" setting, perhaps all the way down to 0.

davescm

Community Expert

.....and I still agree with Dag - if you can avoid resampling then do avoid it

Dave

T

theStigNorwayAuthor

Participating Frequently

Sooo, what you are all saying is that my picture is wasted? There is no way to get it ready for print at that size?
If you read all of my initial post, JJMack, you would have seen that going back and take new pictures is impossible. I need to fix this one.
That's why I'm seeking help, but unfortunately you are all on a much higher level than me, and I don't understand quite what you guys are saying :/

davescm

Community Expert

We are saying look at the image at normal viewing distance. Large images like that are rarely viewed close up (unless it is in a narrow corridor and it is viewed whilst walking close past).

If it is to be viewed from a distance then you don't need to upscale to 300 ppi. Somewhere in the region of 60 ppi will be fine.

I could not see the exact crop size but it looked like you would be fairly close to 60 ppi without any re-sampling. This will not look good viewed from 12 inches - but step back and view it - it will probably be OK.

If you really need it to be viewed from 12 inches then you are probably going to need to reshoot it. Resampling will soften it.

Dave

D Fosse

Community Expert

If your example is used as-is, you will end up with a little less than 60 ppi.

The key is the intended viewing distance. You can forget about 300 ppi right away, that's for books and magazines right under your nose. I don't have the formula in my head, but it doesn't take more than a few steps backward before 60 ppi becomes acceptable.

If the file is carefully sharpened and prepared optimally, I would not upsample it, if it could be at all avoided. As you saw for yourself, upsampling almost always results in these worm-like artifacts. That never looks pretty. I prefer honest pixels.

The benefits of incremental upsampling is a persistent myth. It mostly increases the risk of artifacts.

davescm

Community Expert

The forumula Dag mentions is based on the angle that the eye can resolve and is ppi = 2/(distance x 0.000291)

Where distance is the viewing distance in inches. If unsure of the viewing distance try 1 - 1.5 x the diagonal.

So for the OPs dimensions the diagonal is 228cm = 90 inches.

Using a viewing distance of 90 to 135 inches

That formula gives 290x0.000291)= 76ppi to 2(135x0.000291)= 51ppi

You were pretty accurate without the formula Dag

Dave

D Fosse

Community Expert

davescm wrote
You were pretty accurate without the formula Dag

Phew...I got away with that one...

But people always overestimate the ppi requirement, and usually go for upsampling long before it's really needed - and as a result, ruin it. Leaving the file as it is, is often the best thing to do.

JJMack

Community Expert

A large image like that would not been to be printed at a high resolution a 100DPI or 40 pixel per CM would most likely be good. So you would need good image pixels. 8800px by 2400 you should Stitch two Landscape image to get them have a 10 to 15% overlap.

With two images carefully taken Photomerge should do a good stitching job.

JJMack

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