Print a sample to test resolution

I should be able to figure this out, but I can't.

A friend has a request for a 48"x72" print from what was originally a 24 Mpix file from a Sony A6xxx camera. If I do the math, to get 150 DPI, which is what he thinks he needs, it would take a 72 Mpix file to make the print.

I want to make a 13x19 print of a portion of the 24 Mpix file (as if it were being printed 48x72) to see what it will look like. How do I go about doing that? Step by step instructions would be most appreciated.

I read that you can up Rez the file in Potoshop and that it does a better than fair job. Is that what we need to do? I guess that's why I want to do the test print.

Thanks.

13 inches X 150 ppi = 1950 pixels
19 inches X 150 ppi = 2850 pixels

So, use the rectangular marquee tool. Set it's dimensions to 1950 pixels by 2850 pixels.
Click somewhere in the image to make a selection, then left click and drag it around to where you like it.
Then Image/Crop and save for print (jpeg?).

Volia, you have a 13x19 image at 150 ppi. Print and judge.

If you can afford it, uprez that to 300 ppi using Image/Resize and print again. Now you have 2 prints to compare.

Take note of which resizing vs resampling method you use in Photoshop. If resampling, you can resample once to the sizes wanted, or you also can resample up in increments, mixing the modes each time and utilize some post processing steps in between.

Case in point below and in the next reply.

Let's say I want to take this image and crop a part out, then resize it up by 200%. I could just crop and use the resize image, not noticing the default bicubic mode that is there, or even just pick one I think will work.

Here is the result of just doubling the image size of the crop above in a single resampling up to 200%. The 2nd image is where I resize it up in 3 steps, using different resizing modes, but also post processing as I go along. This allows me to keep the noise at bay, while keeping detail.

Had I wanted to keep the entire image even and not crop anything, but do the same steps, I would have a 12000 pixel wide resulting image with most of the detail still very relevant, but noise wasn't any worse, maybe better.

Step 1 133% = resizing for enlargement option, then some sharpness, contrast, NR
Step 2 166% = resizing for hard edges option and cleanup
Step 3 200% = resizing smooth gradients option and final cleanup

He covers upsizing if you need it.

https://www.youtube.co​m …4mV3NsLmXw&feat​ure=relmfu

Thanks a lot guys. We will be testing soon.

I have used Photoshop to "up-res" many times and tried a few different methods. Way back 20 years ago I tried an application to do it. Neither provided results that I would consider that great.

Lately though I saw a guy using Topaz gigapixel to uprez pics of hummingbirds. Holy Moly were they impressive. I would go straight to that and not waste time with just doing it manually.


The way I do a test print is to size the image at whatever my final output is going to be, then eliminate most of the image so I can save ink. This can be done by adding a white layer over most of the image area, or can be done by selecting something and pasting it into another document that has the same PPI as the full size original. I use the former if I am confident the first test will be fine and I am testing on an appropriate sized piece of paper, and the latter if I am confident I will be making adjustments and retesting. The latter allows you to reuse a single sheet of paper and just place the adjusted image in a clean spot on the paper.

Also, for high quality paper, 200-250 PPI is where you want to be.

I agree with Left Handed Brisket. If your computer can handle the bandwidth needed for Giga Pixel, it is well worth the money. I have used it on more than a few images, and have gotten to the point that it has become a part of my workflow. I order a lot of prints, and quite a few large ones. I’ve become confident in the programs ability to deliver.

I was totally shocked at what he was showing.

He posted probably 5-6 different pics and 100 percent crops from the finished product. Amazing.

bpalermini wrote in post #18945687
I should be able to figure this out, but I can't.

A friend has a request for a 48"x72" print from what was originally a 24 Mpix file from a Sony A6xxx camera. If I do the math, to get 150 DPI, which is what he thinks he needs, it would take a 72 Mpix file to make the print.

I want to make a 13x19 print of a portion of the 24 Mpix file (as if it were being printed 48x72) to see what it will look like. How do I go about doing that? Step by step instructions would be most appreciated.

I read that you can up Rez the file in Potoshop and that it does a better than fair job. Is that what we need to do? I guess that's why I want to do the test print.

Thanks.

When you are printing this large, one thing to consider is the relationship between print size/resolution and viewing distance. For a print this large, one would assume that it is not intended to be viewed at one foot, but rather, the rule of thumb seems to be something on the order of 1.5*diagonal (here, SQRT(48^2+72^2) = 86.5 in = 7.2 ft ~ 2m). For larger viewing distances, a print can be made with a resolution that can be astoundingly low and still be perceived as detailed, without artifact, etc. Here is a table of recommended PPI (pixels per inch) as a function of viewing distance:

http://resources.print​handbook.com …/viewing-distance-dpi.php

and

http://www.northlight-images.co.uk …or-what-viewing-distance/

At 2m, the first site recommends 90 PPI. Using 90 PPI as our example here, you may want to print your test images at 90 and 150 PPI and see if there is a perceptible difference in detail from the recommended viewing distance. Obviously, the less upres-ing you need to do, the less information you are requiring photoshop or Gigapixel AI or whatever to fabricate.

At 6000x4000 pixels (the a6XXX sensor output):

@150 PPI ~ 40 x 26 inches (you would have to up-res 1.8x to get a 72 inch print);
@90 PPI ~ 67 x 44 inches (you would have to up-res 1.08x to get a 72 inch print).

You could make a few 8x10 test prints on the output device which will print the large, final print. Make test prints of various important areas of the image at full resolution (either 150 PPI or 90 PPI) and then hang them on the wall where the final print will reside, under the local viewing conditions, to see if the difference in resolution is noticeable. To do this, you will just need to up-res the original image to the final output size (72 x 48) at both 150 PPI and 90 PPI (1.8x and 1.07x) and then make 8x10 inch crops from those up-resed files and print those crops. Same thing for the 19x13, just a larger crop.

It might be easier to think in terms of pixels, not inches @ some resolution, so you just need to multiply the physical print size (say 19 inches x 13 inches) by the output resolution in PPI (say 150 PPI) to get the pixel dimensions of the crop. For example, 19 inches x 150 PPI = 2850 pixels on the long edge of the crop. Etc. For purposes of printing, you will just need to make sure that the file has the correct PPI tag so that the physical dimension of the print (19 x 13 inches) is correct for print.

Because 8x10's are large enough and cheap, you can make a bunch at critical locations of the image and judge the output at its intended viewing distance and lighting conditions before you decide to print that large, expensive print at some PPI - you might find that 90 PPI is enough, or that 150 PPI is still not cutting it and you need to add even more made up pixels.

Also, consider that you want to avoid sharpening for output (print) until the image is at its final output size/resolution. Otherwise, when you up-res you will also enlarge sharpening artifacts and halos that may be present from sharpening too early for output. You can also make test print strips in a single image for your 100% crop prints with various levels of output sharpening to view the effect on the final print. That way you get the optimal sharpness at the desired output resolution for the final, large print.

In the end, you are trying to balance print size with making up pixels.

have fun!

kirk

bpalermini wrote in post #18945687
A friend has a request for a 48"x72" print from what was originally a 24 Mpix file from a Sony A6xxx camera.

An excel spreadsheet for my 24 Mpix D750 and D7200.

Bob,

A theoretical 24MPixel camera computes to one with 4000 x 6000 pixels.

1. If your friend desires 48" x 72" print, you need a source file which is 150 * ( 48 x 72), or 7200 x 10800.
   So you have to first UPSIZE the length (a copy of your source file, so you still have the original) by 270% (2.7x), to 7200 x 10800 file which you would send to your printer to print the final print.
   
2. But you want to print a small section as a lower cost test, so AFTER you upsize your source file, you can cut a section which is 150 * ( 8 x 10) or 1200 pixels x 1500, and send that 1200 pixels x 1500 crop to your printer to make a 150 pixel-per-inch print at 8x10" size, so you can examine what THAT looks like.