need help with LARGE format canvas print preparation

[Morkel Erasmus]

Some help will be appreciated here.


I am busy preparing a massive panoramic canvas print for a client.
I have upscaled photos for canvas printing successfully in the past, but most times it was upscaled by a factor of 0.5 to 1.5 - this time I need to upscale about 3x the resolution.


The native high res image is a panoramic stitch of 3 images from a Canon 7D.
10182 x 3388 pixels...measuring 86x21 cm @ 300dpi


Now I need to print it at 3mx1m for a hallway.
This means upscaling it to 35433x11790.
Is it worth it to upscale at 300dpi for this size print? Or can I go to 240dpi? Which is the best upscale method to ensure best post-print IQ?


I am familiar with the need to heavily oversharpen to make up for the loss of detail when printing on canvas.
Question is - how much do I need to sharpen this upscaled image to print acceptably for normal viewing (ie nobody will be standing a few inches from a canvas like this, you'll view it from a distance)??


Thanks in advance!

[Roger Clark]

Hi Morkel,

That is a large increase in pixels. Here is what I would do. The current size is about 100 mbytes (if 8-bits/pixel; 200 mbytes if 15b/pxl). A 3x enlargement at 300 ppi would result in a 1.86 mbytes files if 16bits/pixels and 300 ppi. It would be 1.5 mbytes if 240 ppi. So I would stick with 300 ppi. Then I would upsize with a cubic spline then sharpen with Richardson-Lucy deconvolution. Next smooth our artifacts in the sharpened image (e.g. sky and other smooth details. Then perhaps a final unsharp mask. You can find Richardson-Lucy deconvolution in ImagesPlus.

Roger

[Morkel Erasmus]

Thanks Roger. I was hoping at least you would weigh in.

Hi Morkel,

That is a large increase in pixels. Here is what I would do. The current size is about 100 mbytes (if 8-bits/pixel; 200 mbytes if 15b/pxl). A 3x enlargement at 300 ppi would result in a 1.86 mbytes files if 16bits/pixels and 300 ppi. It would be 1.5 mbytes if 240 ppi. So I would stick with 300 ppi. Then I would upsize with a cubic spline then sharpen with Richardson-Lucy deconvolution. Next smooth our artifacts in the sharpened image (e.g. sky and other smooth details. Then perhaps a final unsharp mask. You can find Richardson-Lucy deconvolution in ImagesPlus.

Roger

I've read many of your articles on Richardson-Lucy, but haven't dived into it myself.

Question: what is "ImagesPlus"? And is there an "action set" for RL Deconvolution that I can obtain, or is it a separate plugin?
Question: if I do run RL - do I still need to oversharpen to compensate or the canvas 'sucking in the detail'?

[John Chardine]

I find for big up-samples, onOne's Perfect Resize does an excellent job.

[Roger Clark]

Thanks Roger. I was hoping at least you would weigh in.
I've read many of your articles on Richardson-Lucy, but haven't dived into it myself.

Question: what is "ImagesPlus"? And is there an "action set" for RL Deconvolution that I can obtain, or is it a separate plugin?
Question: if I do run RL - do I still need to oversharpen to compensate or the canvas 'sucking in the detail'?

Hi Morkel,

Images plus is an independent program (made for amateur astronomers for image processing astrophotos), but has a lot of applications for regular photography too:
http://www.mlunsold.com/

(I have no relation to this software or company). I wish there was a simple plugin of RL Deconvolution for photoshop, but I do not know of one.

Roger

[Roger Clark]

Question: if I do run RL - do I still need to oversharpen to compensate or the canvas 'sucking in the detail'?

Hi Morkel,
I see I forgot to answer your second question. Oversharpening tries to compensate for low MTF of the printer, so I would say yes, you will likely still need to do that.

Roger

[Mike Milicia]

Is it worth it to upscale at 300dpi for this size print? Or can I go to 240dpi?

With regard to this particular question, you don't really have a choice as to how much to upsize. It is just a question of whether you do it in Photoshop or some other tool explicitly prior to printing or whether the printer driver does it for you.

Printers REQUIRE a certain number of pixels in order to generate an inch of output. This is called the "native resolution" of the printer. For example, Epson printers require 360 pixels in the source image in order to generate 1 inch of output. Let's say that you hand an image file to an Epson printer that has 6000x3000 pixels with the resolution metadata attribute set to 300PPI. The driver looks at the pixel dimensions and the resolution attribute and concludes that you are asking for a 20" x 10" print. Then, since the driver REQUIRES 360 pixels for each inch of output, it proceeds to upsize your image to 7200x3600 pixels before starting the print.

It is normally recommended that you upsize to the printer's native resolution (e.g. 360 PPI for Epson) using Photoshop or some specialized software prior to printing rather than letting the device driver do the final upsizing. If you are using a non-Epson printer, you would ned to do some research to find out the native resolution of the printer.

You can find more related information here :

http://people.csail.mit.edu/ericchan...tml#native_res