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03-27-2019, 09:07 AM - 1 Like   #1
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K1 in print test

How many mega pixels do I need for printing? Not so many. I took a well exposed shot from the K1 and D-FA28-105, converted to JPEG and cropped to equate: 125dpi, 150dpi, 165dpi and 180dpi, with and without sharping on top of standard sharpening, printed 7 images 8"x12". Then viewing the prints at about 10" distance. The comparison reveals that what we read online is mostly wrong.

- The right amount of sharpening make the 125dpi print look better than the 180 dpi print sharpened.
- At 10" viewing distance, 150 dpi (that's only about 2Mpixels) and up all look good with optimal sharpening.
- At arm length viewing distance it is impossible to see a difference between 125 dpi (1.5Mp) sharpened and 180 dpi (3Mp).

- Since 3Mp is already plenty good, 8Mp should be excellent, optimal sharpening (unsharp mask) is the thing that play a primary goal in how the print looks.
- Lens aberration is the most visible and it's more visible with lower dpi => lens quality, format (less aberrations relative to enlargement) are more important that pixel count.

Conclusion: The mega pixel count is secondary for printing, but the lens and optimal post processing is critical. Sufficient dynamic range is get the most out of image post processing.


Last edited by biz-engineer; 03-27-2019 at 09:21 AM.
03-27-2019, 10:02 AM   #2
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Now do the same same test with 20” x 30” or larger and see if your conclusion is the same.
03-27-2019, 10:14 AM - 1 Like   #3
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QuoteOriginally posted by KiloHotelphoto Quote
Now do the same same test with 20” x 30” or larger and see if your conclusion is the same.
Well, the idea to crop the number of pixels and print 8"x12" was to avoid the cost of doing the same number of XXL prints. Is it not a good proxy to print a small rectangle of what would otherwise be a portion of a large print?
03-27-2019, 10:22 AM - 2 Likes   #4
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I have read different studies that conclude the human eye/brain combination can only resolve to about 180dpi. The 300dpi standard comes from the print industry before digital. That's the resolution printers wanted from photographers so they had plenty of room to optimize the photos for magazine publication. It would be interesting to know what the actual final resolution is of the photos on the printed magazine pages.

03-27-2019, 10:29 AM   #5
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QuoteOriginally posted by KiloHotelphoto Quote
Now do the same same test with 20 x 30 or larger and see if your conclusion is the same.
I think the whole point of biz's experiment was to compare dpi, not print sizes. If you can print at 125 dpi then you can print really big versus if you keep it at 300 dpi, then your limit is something like 16 by 24 inches.
03-27-2019, 10:34 AM   #6
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QuoteOriginally posted by biz-engineer Quote
How many mega pixels do I need for printing?
It depends on how large you want to print, the quality of printer you own, viewing distance, and the quality of the image (garbage in...garbage out). It also depends on how picky you are and the paper being used.

QuoteOriginally posted by biz-engineer Quote
- At arm length viewing distance it is impossible to see a difference between 125 dpi (1.5Mp) sharpened and 180 dpi (3Mp).
Arm's length for 8x12", this is expected. At a more common viewing distance, it may be a different story.* Consider too that attaining the lower DPI you are printing to involves significant downsampling with attendant loss of detail. Downsampling is "the great equalizer". Just because quality is indistinguishable does not mean it is adequate or optimal.

FWIW, I have done experiments similar to yours and while my conclusions are different, at the end of the day all that matters is whether one is happy with the output.


Steve

* At 10", one can tell the difference between 150 and 300 easily.
03-27-2019, 10:50 AM   #7
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QuoteOriginally posted by biz-engineer Quote
Well, the idea to crop the number of pixels and print 8"x12" was to avoid the cost of doing the same number of XXL prints. Is it not a good proxy to print a small rectangle of what would otherwise be a portion of a large print?
Well, a couple of questions. Cropping to the size you did, 8x12, at the dpi's you list is equivalent to what size uncropped prints?


And what do you consider an XXL print these days?

FWIW, I have read that 180 dpi can give more than acceptable results, and have seen that myself. OTOH, I would certainly want to see 300 and 180 side by side in a full sized print before I would judge how my final print should be----and that is going to be a bit subject dependent, I would think.
03-27-2019, 10:54 AM   #8
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QuoteOriginally posted by Rondec Quote
I think the whole point of biz's experiment was to compare dpi, not print sizes. If you can print at 125 dpi then you can print really big versus if you keep it at 300 dpi, then your limit is something like 16 by 24 inches.
Yes, exactly.

QuoteOriginally posted by texandrews Quote
Well, a couple of questions. Cropping to the size you did, 8x12, at the dpi's you list is equivalent to what size uncropped prints?
Plse see detail below.


I cropped rectangles from a full size K1 image (.DNG), without downsizing anything, with and without unsharp mask after conversion to jpeg:
- 3:2 crop of 2126 x 1419 pixels => JPEG => Print 8"x 12" (A4): that's 180 dpi. The full size print would be 40.89" x 27.29" ( 104 cm x 70 cm )
- 3:2 crop of 1920 x 1282 pixels => JPEG => Print 8"x 12" (A4): that's 162 dpi. The full size print would be 45.43" x 30.32" ( 116 cm x 77 cm )
- 3:2 crop of 1771 x 1182 pixels => JPEG => Print 8"x 12" (A4): that's 150 dpi. The full size print would be 49.06" x 32.74" ( 125 cm x 83 cm )
- 3:2 crop of 1498 x 1000 pixels => JPEG => Print 8"x 12" (A4): that's 120 dpi. The full size print would be 61.33" x 40.93" ( 156 cm x 104 cm ) , that's a pretty decent poster.

---------- Post added 27-03-19 at 19:00 ----------

QuoteOriginally posted by stevebrot Quote
Arm's length for 8x12", this is expected
Please let me clarify. I looked at the A4 prints as close as my eye allow (using glasses for looking close, prescription end 2018 :-) ), so the correction gets me good vision as close as about 5 inches.
Then I looked at the same A4 prints on the wall at arm's length to have an idea of how the big print would look like on the wall... and I think I would be impressive even printed 156cm x 104cm at 120 dpi, but the 162 dpi and 180 dpi would be plain crispy even looking close.

03-27-2019, 11:07 AM - 1 Like   #9
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QuoteOriginally posted by biz-engineer Quote
- Since 3Mp is already plenty good, 8Mp should be excellent, optimal sharpening (unsharp mask) is the thing that play a primary goal in how the print looks.
I have done a fair amount of work with a 4Mpx camera, some of which I am very pleased with. I don't print those images larger than 8x10" paper and at 200dpi from the 2272x1704 capture, I can render a pretty decent print with reasonable crop borders. I won't go larger...the upsampling will not be pretty and it would be a waste of paper and ink. Likewise, I can and have printed 10Mpx on 13x19" paper with very decent results and reasonable crop borders, but am not tempted to go larger. Again, it would be a waste of paper and ink.

A volume digital photo service near me (Costco) will print my 4Mpx images to poster size (~60" diagonal) with incredible colors and pop, but I am not tempted.


Steve
03-27-2019, 11:10 AM   #10
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QuoteOriginally posted by stevebrot Quote
* At 10", one can tell the difference between 150 and 300 easily.
Yes, for sure we can tell the difference between 120 dpi and 180 dpi already, but the difference gets smaller to invisible by changing sharpening amount/method, the added accentuation draw the eye which modifies our perception of detail.
03-27-2019, 11:17 AM   #11
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The point biz was making is that it is not only about pixel count. Post processing and other things are just as important.
For exhibition use I have made 95 cm x 150 cm prints from my K-10 files with very good results. It did take some effort and tweaking in pp, but for the naked eye the result is indistinguishable from K-1 shots.
03-27-2019, 11:23 AM - 1 Like   #12
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QuoteOriginally posted by biz-engineer Quote
Please let me clarify. I looked at the A4 prints as close as my eye allow (using glasses for looking close, prescription end 2018 :-) ), so the correction gets me good vision as close as about 5 inches.
Then I looked at the same A4 prints on the wall at arm's length to have an idea of how the big print would look like on the wall... and I think I would be impressive even printed 156cm x 104cm at 120 dpi, but the 162 dpi and 180 dpi would be plain crispy even looking close.
Thanks, this is helpful.

For those reading this thread who might wish a little extra information regarding print resolution, there are some interesting and very enlightening comments on the thread below, particularly from user @TonyW. I learned a lot from their comments that I intend to incorporate into my work flow for printing.

https://www.pentaxforums.com/forums/32-digital-processing-software-printing/...dpi-print.html

TonyW's comments regarding avoidance of giving the printer driver license are pertinent. They gave me a good schooling.


Steve

Last edited by stevebrot; 03-27-2019 at 01:08 PM.
03-27-2019, 11:30 AM - 2 Likes   #13
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QuoteOriginally posted by PePe Quote
For exhibition use I have made 95 cm x 150 cm prints from my K-10 files with very good results.
This comment reminds me of when I was shopping for my K10D. I asked the counter person at the camera store what the maximum enlargement might be from 10Mpx. Their response was to point to several 3x5 foot display prints on the wall behind them. I figured that was big enough.


Steve
03-27-2019, 11:33 AM   #14
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QuoteOriginally posted by stevebrot Quote
TonyW's comments regarding avoidance of giving the printer driver license bear attention.
Correct. I only thought about the native dpi relative to printer dpi after the prints were done
I guess what happened in all of my print samples is that the printer up-sampled all of them to match the print head step resolution, so that there is no visible pixelization, all prints are all buttery smooth, but on the 120 dpi there is something at the subject edges that doesn't look natural (lens aberration, or too much accentuation of the edge). I could still produce one more print with up-sampling to match the printer and compare the two prints with up-sampling and without.
03-27-2019, 12:37 PM   #15
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QuoteOriginally posted by biz-engineer Quote
Correct. I only thought about the native dpi relative to printer dpi after the prints were done
I tend to do the same and also forgot that the printer renders pixels, not dots.


Steve
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