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Resizing will Always reduce image quality

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ohmydentist

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I see so many posts like:

"you could just downsize 36mp photo to 12mp to match the noise level. . . ."
"if 36mp is too big to share, just downsample it . . . . "

and so on. But it's my understanding that resizing will ALWAYS reduce image quality, since photo files are not vector graphics.

Am I wrong?

--
^ ^

Just Shoot !
 
Not necessarily. Downsizing has benefits - I'll leave it to the more technical folks here to explain why. Upsizing of course has issues.

But ponder this: what do you think happens when you print your print on your high end Epson/Canon or whatever desktop or large format photo printer? The answer: the printer driver itself is doing resizing. It's not a cut and dried thing.

-m
 
ok, I'll be very interested in knowing what IQ benefit downsizing brings.

Good point about printers resizing photos. But I believe informed ones carefully crop or choose right dpi for the print size they want, so that resizing doesn't occur.

--
^ ^

Just Shoot !
 
The camera has a few options to lower the resolution so your files will be smaller in camera.If you use it in DX mode it drops to 15mp.

If you downsize an image it can improve IQ slightly.It's when you upsize an image you will get most problems
--
Diverroy
 
Different size available in camera are just for jpgs. As far as I know, no Nikon dslr offers small RAW.

I cannot agree that you could improve IQ by downsizing. I'm not talking about what looks good to our eyes, I'm talking about technical IQ(at 100% for example).

--
^ ^

Just Shoot !
 
ohmydentist said:
I'm not talking about what looks good to our eyes, I'm talking about technical IQ.

Just Shoot !
Click to expand...
Why don't you just stick with your peers at NASA and the Cyclotron in Switzerland? It's just common photo folks here that are only interested in 'what looks good to our eyes'. We're not up to your technical level.

And then your payoff is 'Just Shoot !'. LOL

--
Philip

 
1) You can go from a theoretical, entirely numbers-driven standpoint that downsizing doesn't yield any benefits (or maybe it does, I've seen articles arguing this), or...

2) You can go from a human-perception standpoint that downsizing does in fact increase perceived quality.

("In theory, theory and practice are the same, but in practice, they aren't.")

-

A little exercise - Bring up an not-entirely-in-focus photo on your computer screen, full-screened (without upsizing it). Look at this image from about 18-24 inches away.

Now, scoot your chair back about 5-6 feet and look at the same image.

The images will look better because their apparent DPI has increased, or their DPI exceeds our eye's ability to resolve it, or any number of angles one wants to take to try to explain it.

Even if the photo hasn't actually been improved, it is perceived as improved. And, since photography is a completely perception-grounded experience, resizing will in fact increase quality.

--
JL Smith
http://jl-smith.smugmug.com
 
Depends what you call image quality.

We downsample a camera resolution from resolution A to resolution B.
You lose resolution, colour information and all that.

But at an image scale at resolution B, your SNR goes up as does the DR.

And its not going to be worse regarding resolution and colour information, than a shot than a camera that started out at resolution B (all else being equal).
 
If we're happy with what looks good to our naked eyes, we won't be in this hardware forum comparing, analyzing, charting. . . and so on.

Any cheap dslr or some good P&S will produce photos that look good on our monitors and in decent size prints.

--
^ ^

Just Shoot !
 
ohmydentist said:
I cannot agree that you could improve IQ by downsizing. I'm not talking about what looks good to our eyes, I'm talking about technical IQ(at 100% for example).
Click to expand...
With a Bayer sensor, a group of four adjacent photosites include 1 red, 1 blue and 2 green. The image viewed at 100% contains interpolated data and contains a lot of fake data. Downsizing by a factor of 2 in both X and Y eliminates the fake green data. Downsizing by a factor of 4 eliminates the fake blue and red data. The human eye has lower color resolution and luminance resolution, so we're ok with this method.
 
ohmydentist said:
ok, I'll be very interested in knowing what IQ benefit downsizing brings.
Click to expand...
Increased sharpness by shrinkage of blurred edges, decreased noise by averaging of pixel information. One reason why prints look so much better than images at 100% on monitors.
ohmydentist said:
Good point about printers resizing photos. But I believe informed ones carefully crop or choose right dpi for the print size they want, so that resizing doesn't occur.
Click to expand...
Do you think there is magic somewhere in the universe that adapts an image shot at an arbitrary resolution to an output medium created or displayed at a different arbitrary resolution?

For example, if you do not choose a multiple of the printer's native resolution (300ppi for Canon and 360ppi for Epson) then the printer will interpolate for you anyway.

Appropriate resizing makes images look better on every medium.

--
http://kimletkeman.blogspot.com
 
I was wondering along the same lines, down-sampling each set of 2x2 pixels to 1 pixel, aka downsampling from 36MP to 9MP might be the best option.
sting said:
ohmydentist said:
I cannot agree that you could improve IQ by downsizing. I'm not talking about what looks good to our eyes, I'm talking about technical IQ(at 100% for example).
Click to expand...
With a Bayer sensor, a group of four adjacent photosites include 1 red, 1 blue and 2 green. The image viewed at 100% contains interpolated data and contains a lot of fake data. Downsizing by a factor of 2 in both X and Y eliminates the fake green data. Downsizing by a factor of 4 eliminates the fake blue and red data. The human eye has lower color resolution and luminance resolution, so we're ok with this method.
Click to expand...
 
TrojMacReady said:
Depends what you call image quality.

We downsample a camera resolution from resolution A to resolution B.
You lose resolution, colour information and all that.

But at an image scale at resolution B, your SNR goes up as does the DR.

And its not going to be worse regarding resolution and colour information, than a shot than a camera that started out at resolution B (all else being equal).
Click to expand...
Nicely said.

--
Dj Joofa
 
ohmydentist said:
Rather than just making blunt statement, why not offer some source to back it up?
Click to expand...
DxOmark

1. Click on the link below
http://alturl.com/ayr89
it will bring to a page comparing D3X abd D700

2. Click on the tab called "Measurement"

3. There are tabs of "SNR 18%", "Dynamic Range", "Tonal Range", and "Color Sensitivity"

They are image quality measurements. Click on any one of those image qualities tab

4. On top left there are 2 buttons, the "Screen" and "Print"

5. Click on "Screen"

6. Click on "Print"

7. See the difference
The "Screen" button will show the image quality in original Pixel size
The "Print" button will show the image quality in REDUCED size

It will show you that D3X image qualities will match D700 when it's REDUCED to the same size of D700, but it will lack behind D700 in original pixel size
 
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