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Author Topic: Upres or downres  (Read 2745 times)
Gurglamei
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« on: February 23, 2010, 02:35:51 PM »
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I always thought that the more megapixels the better.  However in an other thread in here - do not remember which - I read that having too many pixels can pose problems of its own.

Now, I wounder what gives the best image quality: Upres 100 % or down res 100%?  Obviously printing at the native resolution is best, but given that a sensor size will not match all needs in print size, is it best to opt for a sensor size that would imply mostly upres og mostly down res (100%)?

(I can actually imagine that ures is easier to perform. Inventing pixels seems easier for software to do that having to decide what to throw away?)


Christopher





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Schewe
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« Reply #1 on: February 23, 2010, 02:44:07 PM »
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Quote from: Gurglamei
Now, I wounder what gives the best image quality: Upres 100 % or down res 100%?


For what purpose? If you have too many pixels, obviously you are going to need to downsample...it's not always a clear cut case in the event you don't have enough pixels...but the question as you asked it doesn't make sense...
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tho_mas
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« Reply #2 on: February 23, 2010, 02:56:19 PM »
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Quote from: Gurglamei
given that a sensor size will not match all needs in print size, is it best to opt for a sensor size that would imply mostly upres og mostly down res (100%)?
basically downrezzing is less critical than uprezzing.
Generally I'd say downrezzing 50% or even 25% and uprezzing 200% is not really critical, i.e. the results will still look good.
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Gurglamei
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« Reply #3 on: February 23, 2010, 03:45:32 PM »
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Quote from: Schewe
For what purpose? If you have too many pixels, obviously you are going to need to downsample...it's not always a clear cut case in the event you don't have enough pixels...but the question as you asked it doesn't make sense...

I was thinking how to best match camera sensor resolution to a given printer size for optimal print quality.

Say I have a 24 inch printer and want to make the best possible prints at 3 different sizes: A1, A2 and A3. For an A2 print (approx 24 inches on the long side) I would need some 31 MP to print at 300 dpi with native resolution.  I could upres this 100 % to make a A1 print (24 inches on the short side), and I could downsample 100% (or would that be 50%) to make a print size A3.

Alternatively I could have a sensor with some 65 Mp and be able to print  A1 at native resolution with 300 dpi, and have to downsample 100 % (50%?) to make an A2 print and downsample 200% (100%?) to make an A3 print.

What would make the better print in the respective sizes?

(sorry about the confusion on the downsamling %,  being an early bird it is way past bedtime here in Norway and at that time my brain goes into som kind of reduced capasity mode... :-)

Christopher
« Last Edit: February 23, 2010, 03:57:07 PM by Gurglamei » Logged
Schewe
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« Reply #4 on: February 23, 2010, 04:32:36 PM »
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Quote from: Gurglamei
What would make the better print in the respective sizes?

Lightroom where you can very easily output at the native resolution regardless of the desired print dimension...

In practice though I would never downsample merely to hit some sort of output resolution. Why waste the pixels?

Upsampling "can" help the output if you A) do it well and  do proper sharpening after the upsample...
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BartvanderWolf
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« Reply #5 on: February 23, 2010, 05:46:31 PM »
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Quote from: Schewe
Lightroom where you can very easily output at the native resolution regardless of the desired print dimension...

In practice though I would never downsample merely to hit some sort of output resolution. Why waste the pixels?

There can be reasons to downsample, but it depends on the situation. When the downsampling factor is significant, and the subject in the image is sensitive to the creation of aliasing artifacts, and the output modality doesn't dither or anti-aliase the result enough, then it's beneficial to do a correct downsampling before sensing the data to the print driver's 'black box' (bi-linear?) downsampling algorithm. Granted, a lot of conditions need to be met. A simple print test with a critical image can tell whether one runs a risk. Another reason can be to reduce the amount of print data, e.g. when printing over a network or when the spoolfile can get too large in a large batch printjob that has to run unattended.

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Upsampling "can" help the output if you A) do it well and  do proper sharpening after the upsample...

That's correct, it has to be done well (i.e. not introduce artifacts in the process, and possibly create useful extra data), and a huge benefit is that sharpening can be done at the final print resolution which is more precise and gives less chance of creating sharpening artifacts. This does assume proper interpolation to the native printer (driver) resolution for a given paper type.

Cheers,
Bart
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Gurglamei
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« Reply #6 on: February 25, 2010, 01:23:38 PM »
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Thank you!

Christopher
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Dick Roadnight
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« Reply #7 on: February 25, 2010, 01:47:23 PM »
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Quote from: Schewe
In practice though I would never downsample merely to hit some sort of output resolution. Why waste the pixels?
I sent the council a 50Mpx picture they wanted of a bus, and they said that their printers could not do anything with a file that large!
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Dick Roadnight
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« Reply #8 on: February 25, 2010, 01:50:23 PM »
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Quote from: Gurglamei
Alternatively I could have a sensor with some 65 Mp and be able to print  A1 at native resolution with 300 dpi, and have to downsample 100 % (50%?) to make an A2 print and downsample 200% (100%?) to make an A3 print.

Christopher
With a Phase or Hasselblad 4:3 sensor, the picture fits well across a 24" Epson printer @360dpi, or, I think, along it @240.
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Schewe
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« Reply #9 on: February 25, 2010, 02:06:03 PM »
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Quote from: Dick Roadnight
I sent the council a 50Mpx picture they wanted of a bus, and they said that their printers could not do anything with a file that large!

We were talking about printing to an ink jet printer...not dealing with halftone repro. In the case of halftone, 2x the line screen ruling is optimal for PPI. So, the image would need to be resampled either in Photoshop or in the graphics app like InDesign...
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Peter_DL
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« Reply #10 on: February 25, 2010, 03:53:05 PM »
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Quote from: Gurglamei
Alternatively I could have a sensor with some 65 Mp and be able to print  A1 at native resolution with 300 dpi, and have to downsample 100 % (50%?) to make an A2 print and downsample 200% (100%?) to make an A3 print.
What would make the better print in the respective sizes?
Isn't that also a question about sensor size, pixel density, noise and dynamic range...

Peter

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