preparing image for large print

I'm preparing images for a large print (90x 60 cm, roughly 35 x 24 inch) for my first customer. Since this is the first time I do this, I was hoping for some advice.
What I've found so far browsing through older posts and other web resources is that I should up res the images to the correct size, using some form of interpolation. Also I need to sharpen the image after resizing, but I'm a bit inconclusive about what settings to use.
Which interpolation technique do you use for such large prints?
Which sharpening settings? My Photoshop book tells me that I need to use a 3 px radius setting for a 300 dpi print, but I see other settings mentioned here on BPN.
If I understand correctly, I need to slightly oversharpen the image for print, because of the bleeding of the ink on the paper. However, I'll be using direct printing on Forex foam plate, for which I'm unsure whether there will be any bleeding.
Color management is set, I have an ICC profile for this process from the printer.

Of course I want the images to look stunning, so any help and advice are greatly appreciated (also beyond the answers to the above questions)!

I upres in one step. In the old days, last century, there was a lot of "information" about doing an upres in 10% steps, and a lot of hype about various programs that would do better than PS. I don't think that's true now, if it ever was. Recent versions of PS will suggest a sampling algorithm depending on whether you are going larger or smaller. I'd accept that and inspect the final at 100% and try others for comparison.

I'd ask the printer about bleeding, but if it's a glossy you probably won't have a significant amount. They might also be able to suggest the best sampling algorithm for their process.

Good luck -- it's always exciting to see a real print!

Hi, Jerry if your not printing these yourself at home on a inkjet printer then contact your lab for the methods they recommend for up sizing and to to what dpi as well as what sharpening method and amount. If this is for a client and your trying to make a great first impression I would be using a pro lab and working with them to produce a master print file that they would upsize and sharpen for the final print size. If that's not in the budget then you really can't go wrong using PS to up size to their recommended dpi and using a good sharpening plugin to finale output sharpening depending on the media it's being printed on and the method. I prefer PhotoKit Sharpening Pro been using for years.

Thanks Diane and Don.
I'm not able to print at this size myself, nor am I able to print on other materials, so I use a semi-pro lab. The print on Forex foam plate has a matte finish. The method of printing is not comparable to inkjet printing. In the words of the printer they use a '1200 dpi piezo-electrical printing process'. Although they are a pro lab, they don't do any up res or additional sharpening on the master file I supply, so they advised me to upsize the photo myself to the correct size. Apparently they expect me to be a pro too! The only requirement they state for an optimal result is that the file needs to be 300dpi, and they supply an ICC profile for each specific printing process.
Don, in your sharpening routine after upsizing, do you indeed oversharpen a little for prints as I read in some books and internet resources?

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Originally Posted by Jerry van Dijk

Thanks Diane and Don.
I'm not able to print at this size myself, nor am I able to print on other materials, so I use a semi-pro lab. The print on Forex foam plate has a matte finish. The method of printing is not comparable to inkjet printing. In the words of the printer they use a '1200 dpi piezo-electrical printing process'. Although they are a pro lab, they don't do any up res or additional sharpening on the master file I supply, so they advised me to upsize the photo myself to the correct size. Apparently they expect me to be a pro too! The only requirement they state for an optimal result is that the file needs to be 300dpi, and they supply an ICC profile for each specific printing process.
Don, in your sharpening routine after upsizing, do you indeed oversharpen a little for prints as I read in some books and internet resources?

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Hi Jerry, I let the plug in provide the sharpening after I select the printing method and DPI of the image depending on the printing method the image will appear slightly over sharpen. i am not familiar with the print method your using can you provide a link.

Hi Jerry,

I doubt if the person at the lab knows much, I say this because piezoeletric printing is just another name for Epson inkjet printing. It refers to how the ink droplets are made. It IS inkjet.
https://en.wikipedia.org/wiki/Micro_Piezo

Thanks Arash. I was just parroting the text from their consumer website, which, now I've looked for the English version to post for Don, seems a typical case of 'lost in translation'. The story on their US website is rather different, although not really more informative. But I think you're right, it's just inktjet printing.

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Originally Posted by Don Lacy

Hi Jerry, I let the plug in provide the sharpening after I select the printing method and DPI of the image depending on the printing method the image will appear slightly over sharpen. i am not familiar with the print method your using can you provide a link.

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Thanks Don. I don't think there is a preset for this material. The description of this material is given here on their website.
I've received a sample of this product yesterday. I must say that I'm not really convinced by the durability of this material nor the printing quality, so I may go for one of their other options (photoprint on alu-dibond, or a photoprint coverd with acrylic glass). It will increase the price for a print considerably, so I'll have to confer with the client.

Hi Jerry,

I do allot of printing and selling of my art. I am a rep for a company that specializes in canvas printing and I also print on paper and face mount acrylic.

I find that customers are very happy with a high quality canvas print depending on the size and wants of the customer. I sell more canvas prints than anything.
If a tight canvas weave is used and a high quality printer, the results are awesome and many images take on a painterly effect while still being nice and sharp. I sell to many photographers including many on this site. You may find that it is an easy and inexpensive way to get your art into customers hands.

Acrylic face mount printing is awesome but has a few downsides. The biggest downside is that it is more expensive. Way more! I Use Art mill and my rep can help you and offer you a great price on a quality job but they are not cheap. I just got a 40"x30" one back of a Kestrel with a dragonfly. It looks fantastic and is printed on metal paper which is mounted to a Dibond backer and then is covered in acrylic. The other downside to them that I didn't realize at first is the location in your home or office for your print. It needs to be in room without windows across or even at an angle. The glare on the acrylic makes the image hard to see. Also acrylics are best seen under lighting. I have most of my prints under lights.

Preparing your images for printing is simple using PS. First assess the sharpness and probably add a bit more. Not crunchy but just on the edge. .3 diameter at 100% using smart sharpen should be good. Now take that finished image and open up the "Image size" dialog. Change the size to the size you want in inches. Then change the resolution to 300dpi. Now check resample and use preserve details (enlargement). Thats it! Save it and it's ready for the printer.

I offer a special deal to BPN members for canvas prints. 3- 36"X24" prints with full bleeds and a 1.5 inch gallery wrap. This is the wider stretcher type and the image is printed on the sides so it can be hung without the need for a frame.
They do great job and the canvas is as tight as a drum. $250.00 for three beautiful large canvas Shipped to your, or your customers door.

I added a few pics of some canvas prints in my home. These are 36X24 and the Kestrel in the middle is a 40X30. I did put them in floater frames. I added a closer shot. These are taken with my phone, but you can kind of see the nice feather details in the owls face

If you are interested or need more help you can PM me anytime.

Hope this helps

David

Thanks for your response David. I talked to my customer today and showed her some samples. We identified the glare issue as a dealbreaker too. Despite the quite conspicuous difference in sharpness and contrast between a photo print under acrylic glass and a direct print on Forex, we chose to go for the Forex because of the glare issue and the weight of these large prints. Canvas could have been an option too. The thing is, with such large prints, you'll always be viewing them from a larger distance, at which the differences between the two modes of printing were much less obvious than on closer inspection.
Your sharpening tips are greatly appreciated!
Btw. that expression on the owls face is priceless!

HI Jerry, Looks like you have figured out what you and your client need good luck. I have not seen Forex prints before seems interesting right now I am printing all my personal stuff on aluminum i just love the depth of the images.

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Originally Posted by Don Lacy

HI Jerry, Looks like you have figured out what you and your client need good luck. I have not seen Forex prints before seems interesting right now I am printing all my personal stuff on aluminum i just love the depth of the images.

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Thanks Don for your input. All that remains as a chalenge is getting the IQ right on the enlargement!
The printing process for direct print on aluminum and Forex is the same. In the sample prints I got from the printer the Forex prints actually look better than the ones on aluminum. Less grainy. If you are curious, you can order a sample package through the website of the printer I provided above. They only charge the shipping costs. It provides samples of various direct printing methods (aluminum, alu-dibond, Forex), photo prints under acrylic, and a range of photographic paper and canvas.