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Please explain "downsizing"....

hollingwD80

Hartselle, US
432 posts

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hollingwD80 Registered since 30th Apr 2008
Thu 09-Feb-12 02:20 PM

Hello:

In reading these posts, a lot of talk is about downsizing the D800 images. Please explain exactly what you mean by downsizing.....And....Why on earth would anyone want to downsize an image? What's the use of all those megapixels, if you turn around and get rid of some of them?????

Thanks,
Rich

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ericbowles

Atlanta, US
10631 posts

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#1. "RE: Please explain "downsizing"...." | In response to Reply # 0

ericbowles Moderator Awarded for his in-depth knowledge and high level skills in various areas, especially Landscape and Wildlife Photoghraphy Writer Ribbon awarded for for his article contributions to the community Donor Ribbon awarded for his very generous support to the Fundraising Campaign 2015 Nikonian since 25th Nov 2005
Thu 09-Feb-12 01:36 PM

What that is really referring to is applying high megapixels to a print or a standard output size.

You can make the dots of ink smaller, in which case noise becomes insignificant. But printers already have their limits and your optimum remains 260-300 dpi.

So instead you would "downsize" the image - combining 3 pixels of a 36 MP image into a single pixel for rendering in a normal print. This means that noise is a small amount of the result, and virtually disappears.

DxO uses a standard size print to evaluate all the different cameras with different sensor sizes. That print size is 30x20cm or approximately 12x8 inches.

You could pick an alternative size - 30x20 inches inf you wanted. That requires upsizing. That would mean that each pixel of a D3 needs to be converted to 2 pixels - and any noise would result in twice as much noise.

You would not be throwing anything away - just evaluating based on a common output. But if you want to compare images from two FX cameras, the idea is you should compare the same size print from both rather than a much larger print on a camera with more pixels.



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hollingwD80

Hartselle, US
432 posts

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#2. "RE: Please explain "downsizing"...." | In response to Reply # 1

hollingwD80 Registered since 30th Apr 2008
Thu 09-Feb-12 01:46 PM

Thanks Eric....

Rich

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Leonard62

Pa, US
4419 posts

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#3. "RE: Please explain "downsizing"...." | In response to Reply # 0

Leonard62 Gold Member Awarded for excellent contributions and sharing his in-depth knowledge and experience with the community, especially of Nikkor Lenses Writer Ribbon awarded for his contributions to the Nikonians Resources articles library Nikonian since 15th Mar 2009
Thu 09-Feb-12 02:18 PM

Eric is explaining what DxO does to come up with a common print size for comparison purposes.

I downsize in order to view different camera photos on the computer at the same size for comparison purposes.

I use a D3X which has an image size of 6,048 X 4,032 pixels or 24.4 mp.

I compare the images to my D700 with is 4,256 X 2,832 pixels or 12.1 mp.

I do this by viewing my D3X photo in CS5 and looking at the image size of the photo. It shows 6,046 and 4,032. I change that to 4,256 and 2,832. And save it. If my D3X and D700 photos were of the exact same scene I now have two photos of the exact same size and I can compare the quality of both to each other. If I'm looking at the noise of the D3X photo at 100%, the noise is slightly reduced when down sizing to the D700 size.

Unlike the DxO results which show the D700 noise as slightly better then the D3X noise, I find the D3X has ever so slightly less noise then the D700 after downsizing on my computer screen. Here is a comparison of my D3X and D700 side by side after down sizing.

The D3X photo is on the left. This is a comparison of photos taken at ISO 6400 and enlarged 100%.

Click on image to view larger version


I get the same results every time I run these comparison tests.

Len



Attachment#1 (jpg file)

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