Megapixels to Print Size

[jd101io]

All:

Thank you for helping me understand the relationship between actual pixels and print size.  Here is another beginner question for which I seek help.

Assume that I have two identical images, the first taken with a 24MP (6048x4032) DSLR, and the second taken on 6x6cm film and drum scanned at 11334x11334 (as per the West Coast Imaging web site, "ased on 300MB 8bit scan of 6x6 slide film scanned at 5250 dpi on a Heidelberg Tango Drum Scanner.").  Also assume that output will be printed at 16"x20" on WCI's Chromira at 300 dpi.

It would seem that the 24MP DSLR image will print at 302 dpi, just in excess of the 300 dpi limit of the Chromira.  The scanned film image will print at 566 dpi, well in excess of the 300 dpi limit of the Chromira.  My question is what happens to the "excess" dpi;  put another way, once over the 300 dpi limit of the printer, do the prints look any different?

Thanks again,

JD

[Dick Roadnight]

It would seem that the 24MP DSLR image will print at 302 dpi, just in excess of the 300 dpi limit of the Chromira.  The scanned film image will print at 566 dpi, well in excess of the 300 dpi limit of the Chromira.  My question is what happens to the "excess" dpi;  put another way, once over the 300 dpi limit of the printer, do the prints look any different?

If a client insist on an exact size...

If you have control, try to print at your printer's optimum (or maximum) ppi...

You could print the 24 mpx at 300 ppi at slightly less than 20 * 16, or leave a border.

Scans can be expensive, but with some scanners you can scan at exactly the pixel dimensions you want - of course you could do this optically if you were re-photographing.

A good printer driver will make quite a good job of resampling the image to the required output ppi - you could try re-sampling in photoshop to see if the results are any different.

If you have 566 scanner pixels per print inch, and you print at 300, I expect the results to be worse than if you scanned at 300.

Could you print so that you have 600 scanner pixels per print inch? ...even if you could only print at 300, it would be an easier re-sampling operation that would look better in the end result.

Alternatively, you could find someone with an Epson, and print @ 360.

...but most photographers do not care (and are not concerned about marginal differences in quality) and most customers would not notice.

One of the reasons I will be upgrading my camera is that if will enable me to fill the width of my Epson printer @ 360 original camera pixels per print inch.

[jd101io]

Don, while I appreciate the quick reply, I am a beginner to digital photography, although not at all a beginner to photography, and an amateur as well, and simply don't understand your rather technical reply.  Thanks,  JD

[Jeremy Payne]

Don, while I appreciate the quick reply, I am a beginner to digital photography, although not at all a beginner to photography, and an amateur as well, and simply don't understand your rather technical reply.  Thanks,  JD

Let me try a simpler version ... and if I get anything wrong, I'm SURE someone will correct me ...  

Every printer has a native resolution .... likely around 300-360 dpi (and some can go higher).

When you send a file to the printer, if it isn't in the printer's native resolution it gets re-scaled to that resolution by the driver.

Many people think that driver re-scaling is inferior to other software like Photoshop or Lightroom and do their re-scaling before sending to the printer.

Additional tid-bits ...

Many people think an image enlargement that is natively 240 dpi is enough for a photograph - and will go down to 180 dpi for big prints.

Others seem to think they can see the difference between 240 and 360.  I doubt any claims to be able to 'see' the difference above 360.

Personally, I try to stay at 240 dpi and above and re-scale images to my printer's native resolution using Lightroom when time to print.

[jd101io]

Jeremy, what happens in the re-scaling process to the extra information/data/bytes/whatever representing the difference between 566 dpi and 302 dpi when the 6x6 scan job is sent to the 300 dpi printer?  Is all that extra discarded?  And, to my original question, do the two final 16x20 prints look any different?  -JD

[bradleygibson]

In all likelyhood West Coast Imaging's printer driver would scale the data down to 300dpi.  While it's not quite as simple as throwing the extra data away, it is doing something pretty close.  One could say the excess information is being discarded if it's OK to ignore the fact that the downsampled data will probably look better than it would if it had simply been scanned at true 300 ppi, but, of course, not as good as the 5250 ppi).

The prints will look different, but not just because of the interpolation (discarding) of information.  I'd suggest that actually would have little to do with the difference.  Your 6x6 and 35mm lenses would produce a different look, as would the 6x6 scanned film versus the 35mm sensor.  In the end, I belive you would be able to distinguish the two prints quite readily

[bradleygibson]

deleted.

[Jeremy Payne]

In the end, I belive you would be able to distinguish the two prints quite readily

I would also add that just because one scans at 5250 dpi doesn't mean the scanned film necessarily has that much information content ... so the scanner resolution is likely overstating the information content of that resulting image file.

[jd101io]

I would assume that there is no way to ascertain the actual information content expressed in megapixels of a piece of 6x6 film, and that asking the question in such fashion is merely a different way of asking "MF film vs. small format digital" the answer to which is hopelessly subjective and incindiary.

[Jeremy Payne]

I would assume that there is no way to ascertain the actual information content expressed in megapixels of a piece of 6x6 film, and that asking the question in such fashion is merely a different way of asking "MF film vs. small format digital" the answer to which is hopelessly subjective and incindiary.

Yes ... hence my use of the words "not ... necessarily" and "likely" ...  

My opinion, at 16" x 20" both should give outstanding results and I would prefer the digital personally due to convenience and the ability to control the entire image creation process from capture to print.

[bjanes]

I would also add that just because one scans at 5250 dpi doesn't mean the scanned film necessarily has that much information content ... so the scanner resolution is likely overstating the information content of that resulting image file.

I have scanned many 35mm Velvia transparencies at 4000 ppi with good results but the apparent resolution on large prints is certainly no better than I am getting with my Nikon D3 with a much smaller file size. The pictures were taken over a period of time with the same lenses. Roger Clark has done extensive comparisons of film to digital and has calculated that 35 mm Fuji Velvia has the intensity detail equivalent to a 10 MP Bayer array capture and the color detail detail equal to 16MP. I'm not certain how color detail would show up in a print.

Norman Koren concludes that a full-frame sensor with 8.3 megapixels would have resolution equal to 35mm film and that resolution is not the only criterion for image quality and states that "I find the image quality in my 6.3 megapixel Canon EOS 10D to be equal to 35mm film".

In the 2nd edition of Image Sharpening, Jeff Schewe states that 35 mm film scanned at 6300 ppi (creating a file of 8900 x 5700 pixels) has about the same potential for enlargement as a 6-8M digital capture, but adds the caveat that the rule of thumb was very approximate.

[edwinb]

1 pixel of 16bit qualty data is far more informative than 1 pixel at 8 bits poor quality data
hence a six MP dslr is inferior to the quality from (say) a sinar 6MP 23 cameraback (now obsolete)
one will print an a3 quite nicely and the other will not
this makes comparison of pixels very difficult without addition quality consideration
Edwin

[jd101io]

Thank you all.  Back at the beginning of the decade, this amateur (landscape/structure, 4x5 Provia, drum scan, lighjet) was thinking about moving down to 6x6.  I have been away from photography for the last six years, and boy have things ever changed!  Now the decision is stay with LF, or MF film, or DSLR - assuming I ever do decide.

[jasonrandolph]

Now's the perfect time to go digital if that's what you decide.  With 24MP full-frame DSLRs starting at under $2000, digital is within everyone's grasp.  You shoot differently than you do with film, but I think digital is even more versatile than film ever was.  Either way, you will be able to make very fine prints.

[BernardLanguillier]

A few additional elements of answer:

- Not all printers are equal detailwise, and there is ample evidence from key writters that at least Epson printers benefit from 480 dpi, this has been my experience also,
- The pixels of DSLRs are typically of much higher quality informationwise than the pixels resulting from a scan, not all DSLRs are equal also,
- Rather than leaving it to an unknown printer driver to do a up/downsampling for you, you might as well take control and proceed with the up/downsizing yourself either in PS, or using some dedicated plug-ins. This will enable you to sharpen your image the best possible way taking into account the output res. This is at least the recommendation if you print yourself,
- When dealing with a third party printing service, the best is to ask them the condition in which they would like to receive the image for best possible results.

Cheers,
Bernard