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melissag68601550
Participating Frequently
April 25, 2019
Answered

Large Formatting Printing in Photoshop CC- Need Help a print job this week

  • April 25, 2019
  • 2 replies
  • 1050 views

First time posting a question. I am looking to enlarge a few images for 3 tradeshow backdrops for a client. (First time printing tradeshow graphics) I want to make sure that the images are appropriate for viewing from a 6'-10' distance. I believe a resolution of 120dpi would be sufficient. I am unsure of the sequence of steps to take in Photoshop's Image Size panel.

Here is what I am working with:

  • The dimensions of each backdrop: width of 66.9291" (1,70m) X height of 47.2441" (1,20m)
  • The image sizes/resolutions to be altered:

1. 250dpi   13.628" x 9.008"

2. 300 dpi   13.217" x 9.023"

3. 136dpi     10.993" x 6.603"

Questions:

-Is 120dpi a good resolution?

-Which steps do I take first in the Image Size Panel? Change the resolution first? or First resample image using Bicubic smoother?

-Also, should I Sharpen the image after to help with the quality? Using, Filter> Sharpen>unsharpen mask?

Before I go back to the client asking if they have bigger image sizes I wanted to see if what I have to work with will get the job done.

Thank you!

This topic has been closed for replies.
Correct answer davescm

Hi

There is a handy formula for calculating ppi based on viewing distance.

ppi = 2/(viewing distance in inches x 0.000291)

At your closest quoted viewing distance of  6 feet - that gives  2/(72 x 0.000291) = 95ppi - anything above that will not be visible at that distance. At 66.9 x 47.2 inches you should be looking at 6355 x 4484 pixels.

At 10 feet it gives 57 ppi and an image requirement of 3813 x 2690 pixels.

The existing images that you quote above measure approx :

1. 3407 x 2252 pixels

2. 3965 x 2706 pixels

3. 1495 x 898 pixels

The first two will look fine without and resampling at 10 feet but pixels may be visible at 6 feet. The third will look pixellated.

If you resample - then bear in mind the following. Resampling does not introduce any new detail. All it does is adds more pixels. So you avoid visible pixels at the expense of some image softening and potentially introducing artifacts. How much that softening and any artifacts will impact depends on the image content.

I would recommend you try the following for each image :

Use image size - with resample checked and Preserve details 2.0 set as the resample method, set the resolution to 95ppi and the width to 6355 pixels. Now crop a representative part of the image and make small print of that cropped area.

Now step back in history to the original size  and this time use image size  with resample unchecked, just set the image width to 66.9 inches. Crop the same area and make a small print from the crop.

Now examine both from 6 feet away. Can you see the difference, and if so, which do you prefer?

Dave

2 replies

D Fosse
Community Expert
D FosseCommunity Expert
Community Expert
April 25, 2019

melissag68601550  wrote

The dimensions of each backdrop: width of 66.9291" (1,70m) X height of 47.2441" (1,20m)

I think you can safely go down to 100, which will still look eminently crisp and sharp at that distance, as long as the file is of good initial quality and you sharpen it optimally. The ACR filter is very good. Set Detail low enough so that you avoid halos.

Let's do the math. At 120 ppi, 170 x 120 cm works out to 8030 x 5700 pixels. That's roughly what you get out of the latest generation cameras from Nikon, Sony and Canon. IOW if that's what you have, there's no need to resample at all. With a lower resolution camera, consider stitching.

I always try to avoid resampling if at all possible. Which is most of the time. Resampling always has a price, there's always artifacts. Usually the end result looks better without resampling, even if the resolution is a bit lower. The cleaner pixel structure more than makes up for it.

Above all avoid jpeg, as warunicorn points out.

The output from one of these abovementioned high resolution cameras, is good enough for anything. Magazine spread, wall sized banner, it all looks good. Standing with your nose right up to a large format reproduction is physically uncomfortable. You don't see anything - so you step back, to a point where it begins to make sense to your eyes. In practice, you usually end up at a "normal" distance, meaning the image takes up a certain angle in your field of view. So the optical resolution is more or less constant.

Consider 100 pixels to an inch. Each pixel is 25/100 mm, or roughly 0.25 mm.

    davescm
    Community Expert
    davescmCommunity ExpertCorrect answer
    Community Expert
    April 25, 2019

    Hi

    There is a handy formula for calculating ppi based on viewing distance.

    ppi = 2/(viewing distance in inches x 0.000291)

    At your closest quoted viewing distance of  6 feet - that gives  2/(72 x 0.000291) = 95ppi - anything above that will not be visible at that distance. At 66.9 x 47.2 inches you should be looking at 6355 x 4484 pixels.

    At 10 feet it gives 57 ppi and an image requirement of 3813 x 2690 pixels.

    The existing images that you quote above measure approx :

    1. 3407 x 2252 pixels

    2. 3965 x 2706 pixels

    3. 1495 x 898 pixels

    The first two will look fine without and resampling at 10 feet but pixels may be visible at 6 feet. The third will look pixellated.

    If you resample - then bear in mind the following. Resampling does not introduce any new detail. All it does is adds more pixels. So you avoid visible pixels at the expense of some image softening and potentially introducing artifacts. How much that softening and any artifacts will impact depends on the image content.

    I would recommend you try the following for each image :

    Use image size - with resample checked and Preserve details 2.0 set as the resample method, set the resolution to 95ppi and the width to 6355 pixels. Now crop a representative part of the image and make small print of that cropped area.

    Now step back in history to the original size  and this time use image size  with resample unchecked, just set the image width to 66.9 inches. Crop the same area and make a small print from the crop.

    Now examine both from 6 feet away. Can you see the difference, and if so, which do you prefer?

    Dave

      M
      melissag68601550Author
      Participating Frequently
      April 25, 2019

      Thank you Dave. I do not have Perserve details 2.0 as a resample method (I have CC 2017).

      Question: Will preserve details enlargement provide the same results?

      I tried it both ways as you suggested (except for substituting the resample method as I stated above). Looking at both images side by side on my monitor at 100-120%. The image that had resample unchecked is less grainy, even though this method the resolution is 57ppi.

      Going forward I will avoid Jpeg as warunicorn points out and avoid resampling as you and D Fosse point out.

      Question: Regarding your formula ppi = 2/(viewing distance in inches x 0.000291)

      What does .000291 represent?

      thanks again!

      War Unicorn
      Community Expert
      War UnicornCommunity Expert
      Community Expert
      April 25, 2019

      The general consensus is that the further away the image viewed, the less resolution needed. 120 DPI would sound about right at that distance but maybe others can chime in.

      I work with target dimensions first, followed by resolution, then resampling (which is almost always Bicubic Smoother for enlargements). Again, maybe others can chime in.

      Also, I'm not sure I need to mention this: Blowing up file formats like JPEG will undoubtedly also blow up the compression artifacts inherent in that file format. Try to stick with lossless formats like RAW, BMP and TIFF when possible.

      Blown-up images could always use a bit a sharpening but you don't need to go overboard; a little goes a long way.

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