extreme enlargements of rastered print

[bdforever]

OK, I know this is crazy but I will do it anyway...
In a book I found an A4-sized picture which I would like to blow up to a full wall-sized printing.
I tried to locate a better (=larger) source for the picture but did not succeed.
I know, there's a lot of articles in the forum about big enlargements but I feel that they cannot help me with this crazy project. Has anybody tried a full-blown vectorizer such as the one included in earlier Corel versions? Maybe this would do the trick.
I should mention that the picture is a Casaro painting named the "magnificent seven", but it's not the familiar version with the horses but just the gunmen alone. It is impossible to lacate any print of that.
Thanks in advance,
Harald

[Phosphor]

Forget vector. It'll do you no good for this.

The only thing you can do is scan that image at as high a resolution as you can work with, and take it from there. Ultimately your image in Photoshop will need to be 150 - 200 ppi at full physical dimensions.

For instance, if your final printed image size is intended to be 69" X 96" (1756mm X 2438mm, about the same width:height ratio as an A4 page), you'll need to create an image 10,350 px X 14,400 px for a 150ppi print size. That means for a full A4 page you'll need to scan at about 1200 ppi. Before you get into this I hope you have enough RAM and processor power to deal with the approximately 430MB file you'll be starting with.

The above values are just estimates, the math is probably a wee bit off, and your mileage may vary.

[Burton Ogden]

Harald,

As Phosphor suggested, scan your "original" at the maximum optical resolution of your scanner to get the best starting image possible. That may very well pick up the halftone pattern of your print. Unless you deliberately want to preserve that pattern and magnify it in a "Pop art" effect in your mural print, you will want to eliminate the half tone pattern while preserving your basic image as well as possible. There are several ways to do that, including the relatively expensive Grain Surgery plugin for Photoshop from Visual Infinity. I use Focus Magic which comes in both a Photoshop plugin and a standalone program that includes an effective Despeckle utility. You might want to download the Focus Magic demo and try it.

<http://www.focusmagic.com/exampledespeckle.htm>

After you have cleaned up your scan as best you can, it is time to upsample it a lot, keeping in mind the 30,000-pixel limit of Photoshop and the 2-Gig file size limit. As Phosphor suggested, you can get by with a much smaller pixel count per inch than you might suspect for wall-sized images.

There are several approaches you can take for the upsampling: Qimage, Genuine Fractals, and S-Spline. All of them purportedly do a better job of upsampling than Photoshop's Bicubic (which is not bad, but will be somewhat fuzzy at your extreme magnification).

Have you considered doing this print in sections which you then join together? That is referred to as "tiled printing."

-- Burton -- (not associated with any vendor mentioned)

[Colin Walls]

Although I wouldn't [dare to] argue with the advice you have so far received, I have a further comment:
There is a relationship between required resolution in a print and viewing distance. A wall-sized image is not going to be viewed [or at least appreciated] close up. You can, therefore, "get away" with a much lower PPI. My guess [based upon some experience] is that 75-100 PPI may be surprisingly acceptable. You'll have to "suck it and see" - don't be afraid to break the rules!
Also, all the discussion about how much memory you need assumes you need the whole image in memory at full rez. I assume you haven't got a printer that big, so you will need to work/print in pieces and tile them. There was a thread on this forum a week or 2 back with some good advice on this topic.
I'd love to hear how you get on.

[bdforever]

Hello everyone,
thanks for your productive help.
Actually I planned to have the seven gunmen in life-size, which means the poster is about 2m high and 5m wide.
And you're right. Having 'only' a 36' designjet, I will have to tile the picture into 5-6 strips. But this works quite well, I have done it before.
After reading your mail, the biggest problem doesn't seem to be the enlargement but the de-rasterisation.
I will check the recommended products and try what I can do.
BTW, I have been working with 1.2 Gig Images before, on a Pentium 500 Mhz with 128 MB of RAM and it was surprising how well PS could handle the pic. PS seems to have a great caching algorithm for this. And I did not have a single crash despite 45 mins of calculation time when rotating it.
Yours,
Harald