Large canvas - best method of interpolation?

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Ozei

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I need to get a large-ish (1200mm) canvas done from an image with an existing width of 7300 pixels.

To print at 240ppi I calculate the image width will need to be increased to 11340 pixels. What is the best method of doing it - Photoshop, NX2, or some other specialist software?
 
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are you printing this yourself?

if so you can print at 180 ppi no problem - I doubt you would see any difference in using the 10% method in photoshop compared to a specialist plug in.
 
Perfect resize is pretty awesome....as was it's older brother Genuine Fractals, and the canvas wrap feature is great for extending the printable area around the frame so your image looks neater.

Large prints aren't generally printed at high dpi as they are supposed to be viewed from distance so sharpness and edge detail etc isnt as critical.
 
Give Ben a shout, I'm sure he will be able to advise you and give you a great price at the same time. (Did that with me)
 
POAH said:
are you printing this yourself?

if so you can print at 180 ppi no problem - I doubt you would see any difference in using the 10% method in photoshop compared to a specialist plug in.
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No, I'll be using a lab.

I've read about the 10% increment method - that's what i was planning to use unless there's a better alternative that doesn't cost a fortune.
 
digitalfailure said:
Perfect resize is pretty awesome....as was it's older brother Genuine Fractals, and the canvas wrap feature is great for extending the printable area around the frame so your image looks neater.

Large prints aren't generally printed at high dpi as they are supposed to be viewed from distance so sharpness and edge detail etc isnt as critical.
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I just realised Perfect Resize has a 30 day trial version - I wonder if it's limited in some way (e.g. it uses a watermark).

I'm not sure about the ppi - lowering it too much always seems risky to me, regardless of the print size.
 
Most print labs will resize it for you if you ask, I had one done recently by TradeCanvasPrint who upscaled it using genuine fractals and the print was excellent.
 
Ozei said:
Thanks Swissy. Perfect Resize works out at £94 (ish) at the moment. Is it much better than using Photoshop's Bicubic Smoother?
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Probably no perceivable difference when looking at a print.

I've seen a few comparisons of interpolation software and you can really only see small differences at 100% just make sure you sharpen after interpolation
 
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johnsy said:
Most print labs will resize it for you if you ask, I had one done recently by TradeCanvasPrint who upscaled it using genuine fractals and the print was excellent.
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Client wants to use their own lab, otherwise I'd try Ben.
 
digitalfailure said:
Perfect resize is pretty awesome....... the canvas wrap feature is great for extending the printable area around the frame so your image looks neater.
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Brian,

I've never prepared an image for a canvas before so I could do with a bit of advice - I've downloaded the 30 day trial of Perfect Resize.

The print lab can go to a maximum of 1.2 metres wide for canvas (47.244") and the client wants the whole image on the front. If I add say a 2" wrap border in Perfect Resize, do I need to reduce the image area by 4" (i.e. the front becomes 43.244" wide)?

:thinking:
 
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PS. Is 2" enough for the wrap?
 
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If the frame is 25mm then a 2" extension for the wrap should be ok, though I'd check with your chosen printer to confirm that they are using that size material on such a large frame.
 
digitalfailure said:
If the frame is 25mm then a 2" extension for the wrap should be ok, though I'd check with your chosen printer to confirm that they are using that size material on such a large frame.
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Yes, 25mm seems too flimsy for a canvas this wide - I'll check again with the printer.

Meanwhile, am I right on this calculation (it seems logical to me)?

Ozei said:
The print lab can go to a maximum of 1.2 metres wide for canvas (47.244") and the client wants the whole image on the front. If I add say a 2" wrap border in Perfect Resize, do I need to reduce the image area by 4" (i.e. the front becomes 43.244" wide)?
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I have a 60x40" acrylic box frame on my wall from a picture taken on my D90. Looks pretty good to me!

I just used the crop tool in CS5 and cropped it to 60x40". I had a go with a free trial of that perfect resize and I didn't like what it did to the image but it might have just been me?
 
Mank said:
.... I had a go with a free trial of that perfect resize and I didn't like what it did to the image but it might have just been me?
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I've had a go with the trial version and it seems to be at least as good (and probably better) than using Photoshop. Did you try it with another image?
 
No just on the image I wanted printing big.

It was the edges and details I didn't like. It seemed to smooth it out too much to me. I might have not been doing it right though? :lol:
 
I can't see any smoothing of edge detail on my tests - perhaps you should give it another go with another image.

One advantage of Perfect Resize seems to be this: as mentioned above, a lot of folk increase the size in 10% steps when using Photoshop. I spoke to onOne's tech dept and they recommended using a single step to double or treble the size with Perfect Resize.
 
100% cotton canvas has a heavy textured weave. It withstands lot's of USM and is very forgiving of input dpi.

Remember that regardless of input dpi, the print will be produced at 720dpi as a minimum (that is the dots squirted per inch on a wide format professional printer). We have produced extensive tests printing at larger sizes (60x90 inches) from both jpeg and tiff outputs of the same image. Results show that enlargements from a single original saved as both high level jpeg and uncompressed tiff displayed the same amount of artefacts/softness at this print size. If you shoot a raw file on a 12MP camera and enlarge this to 60x90 inches... regardless of you saving the enlargement as a jpeg or a tiff, the printed result will be almost exactly the same.

For enlargements, I'm not overly keen on 'blow up' software as it tends to introduce a painterly effect on the image. I tend to favour a balance of resampling and then, if necessary, additional interpolation. Interpolating requires the software to guess what goes between the actual pixel density and the desired output pixel density. This introduces artefacts and other softening as phantom data has to be created.

In many instances, resampling to a lower dpi produces a larger print (by dividing over a smaller number). As the software does not need to create phantom information, resampled images can result in sharper looking enlargements. This is especially true for prints onto 100% cotton canvas.

Say you have a 15x10 inch file @ 300dpi and you wish to produce a 30x20 canvas print from this file. Due to the output being onto canvas and not photographic paper, I would resample the image to 180dpi which increases the output size to 25x16.6 inches. I would then interpolate this up to 30x20. This method asks the software to generate a lower amount of phantom information to bulk up the image and results in a high quality print with very few unwanted artefacts (if any).

I appreciate that this may be contrary to information found in various magazines or websites, but the results are undeniable and the tests have been extensive. This becomes an issue when your printer has a dpi that is physically restricted by the hardware (some Lambda printers print exclusively at 254dpi. Sending a 300dpi image results in a larger print size, as it is printed at 254dpi). Interpolation here is the only option.

The best thing to do would be to ask your pro lab what printers they have and if they would be happy to produce a test for you at your desired size. The lab should know how to get the best out of an image on their printers and can advise you accordingly.

Enlargements; it's not always about adding something that isn't there, but being more considered with what is available to you. You'll never know 'till you have a go!
 
I have quite a few A1 canvases printed and the advice I had from the company I use was send files at 100dpi...initially I was extremely sceptical so still enlarged them using the photoshop 10% method, out of interest I did then order one at 100dpi..guess what, to me the 100dpi image actually looked slightly better...all my canvases are now printed at the lower resolution virtually removing the need for any interpolation

Simon
 
Do some research and you will find that Perfect Resize is no better than Lightroom at resizing and is a lot slower at converting.
Just use Lightroom if you have it.
 
Ozei said:
Do you mean ppi (pixels per inch) or dpi (dots per inch)?
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To avoid any resolution semantics, I will state the pixel density of the above as 4500x3000px. As I said in my previous post, some printers and rips ignore the input dpi/ppi/resolution of a file and instead use the mm dimensions the file was saved at. Others, however, cannot do this and are constrained by hardware to print at a set dpi, regardless of the input resolution.

Remember that the larger you go, arguably the less resolution an image requires due to the perceptual cause and effect of viewing distance. I can't recall any conversation where a billboard was called out for its lack of sharpness (ok this is an extreme example, but the principle is the same).

Printing onto canvas is much more forgiving than a C-Type print when enlarging.


Chris.
 
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