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Miles0D45
Participant
October 28, 2023
Answered

Upres 32bit image 3x larger but for 8bit printed file.

  • October 28, 2023
  • 2 replies
  • 480 views

Hi all, 

I've rendered some 32bit files (5000px wide) that I need to be about 3x larger but in 8 bit for some printed pieces (we need to crop into areas so need the size). 
I'm trying to ascertain the best practise for this process. 

My theory is that as a 32 bit image holds 4 times as much info so once upres'ed 3x (Staying in 32 bit) and then converted to 8 bit, the image quality should be the same. However I am losing some quality and sharpness and before I start sharpening anything and crisping the edges of things to much and also doing losts of test I wondered if anyone has done this before and knows of best practice. 

Also to note I've a little colour shift in the highlights still but I've found if i use exposure and gamma as the method of HDR conversion this keeps it fairly true to the render. 

Thanks

This topic has been closed for replies.
Correct answer Miles0D45

I wouldn't call that "best practice", but "what subjectively you were happy with".  :]


Very True 🙂 So to clarify in my opinion it seems to be the best way that the images retain both the original colour/look and feel (again onlyin my opinion  the most important thing) and an acceptable level of quality. The client is happy so we're happy. 

Kinda wish I'd just kept quiet and stayed off the internet 🙂 

2 replies

D Fosse
Community Expert
D FosseCommunity Expert
Community Expert
October 28, 2023
quote

My theory is that as a 32 bit image holds 4 times as much info so once upres'ed 3x (Staying in 32 bit) and then converted to 8 bit, the image quality should be the same.


By @Miles0D45

 

Your theory is flawed. Bit depth is not relevant here, it has no bearing on detail and sharpness. You still have to invent pixels. Upsampling never looks better than the original. There are ways to minimize the damage (like AI), but you can never improve or even fully match the original in terms of visual clarity and crispness. There will always be a bit of degradation.

 

The only justification for upsampling is to avoid visible pixels. Do you see pixels if reproduced as-is? If not, leave it.

 

Is this the old misunderstanding that print "always" has to be 300 ppi, regardless of reproduction size? It's just that, a misunderstanding.

    M
    Miles0D45Author
    Participant
    October 28, 2023

    thanks for your reply:
    Whilst     print doesn't necessarly need to be 300dpi etc etc and the image is as good as it is and an upscaled image is never as good as the original etc etc 
    There are situations like automated pre-flight, client request etc where the situation calls for it and you just need to do it. And while it's fun to have conversations on whether one should or should not upsample, the post mentions I just needed a work around for the situation I had. 

     

    For ref if anyone is interested. Best practice seems to be:

    1. Upscale 32bit image in 150% increments (using automatic upscale,as the englarment algorithm isn't availble in 32bit)  
    2. Once at desired pixel size, convert to 8 bit using the exposure gamma method in HDR toning

    3. Duplicate your background layer, create a smart object, run a large highpass @ 75pixels

    4. Set highpass layer to softlight @ 50% opacity.

    5. Create a level/curves triming the highlight and shadow of each channel to bring back the "pop"
    6. Save and enjoy. 

    Stephen Marsh
    Community Expert
    Stephen MarshCommunity Expert
    Community Expert
    October 28, 2023

    I wouldn't call that "best practice", but "what subjectively you were happy with".  :]

      Stephen Marsh
      Community Expert
      Stephen MarshCommunity Expert
      Community Expert
      October 28, 2023
      quote

      Hi all, 

      I've rendered some 32bit files (5000px wide) that I need to be about 3x larger


      By @Miles0D45

       

      Rendered from what software and what content? Depending on the software and source, optimal results would be to render directly to the desired pixel size in 8bpc so that no pixel interpolation/resampling is required.

      M
      Miles0D45Author
      Participant
      October 28, 2023

      Many thanks for your reply. 

      Re-rendering isn't an option unfortunalty we've considered this, the timings are too tight, there's too many renders and they take to long to come out at the desired size, hence the need to resize in post. 

      Stephen Marsh
      Community Expert
      Stephen MarshCommunity Expert
      Community Expert
      October 28, 2023

      You didn't elaborate on the source? Is this synthetic such as 3D – or is this photographic?

       

      Anyway, all you need to do is decide on the HDR tone mapping (likely Exposure 0 Gamma 1.0) and then resize.

       

      You can test results of 16 bpc vs. 8 bpc resizing using a like-for-like interpolation method. Depending on the content, this could be Preserve Details/Preserve Details v2 or Bicubic Smoother or perhaps Bilinear depending on the trade-off in quality vs speed.

       

      I think that only you can decide what is best based on your originals and processing requirements.

       

      P.S. 15,000px wide for a printed piece is a lot of pixels, this is 1.2 to 1.5 metres wide at close viewing distance. What is the printing method and viewing distance/conditions?

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