Upsizing questions

From RAW conversion to image editing and printing
Alan Shaw
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Joined: Fri Aug 01, 2008 9:17 pm

Upsizing questions

Unread postby Alan Shaw » Tue Oct 20, 2009 5:19 am

Hi all,
My slow but steady transition to a digital workflow continues. I was reading the Exceptional Work All Round thread that hinted at Alamy’s posting requirements about upsizing to a minimum file size. I’m curious about this process, not how it is done, but why.

I’d always assumed that upsizing involved interpolation and, no matter how good the process is, it involves compromises that will degrade the final result. I’d also assumed that it is not possible to add detail that was not there originally. Clearly though, the techniques the Alamy site suggests for upsizing produce a bigger file, and in turn I assume the only reason this is required is to allow a bigger image for publication, i.e. bigger actually is better.

So the first question is whether my assumed reason for Alamy’s requirement to upsize is actually correct. Following on then, how far can this be extended – if a 7D for example can produce good A3 prints, can those techniques be used to produce an equally good A2 print, even if the original file size suggests that would not be the case?

Although I have no interest in uploading any of my work to Alamy I do have a practical reason for asking. I am an occasional contributor to a local magazine and the editor’s normal requirement is for a 2000 by 3000 pixel image. The 7D can do this of course, but when I have provided a cropped image then I am not able to meet his request.

I had assumed the response to the problem of "not enough pixels" was to contemplate an upgrade but upsizing, if done properly, appears to offer an alternative. Is this the case?

Mind you, much as I enjoy the 7D there’s an A700 down the road that keeps calling out “feel me, touch me, BUY ME!” and I’m not sure whether I can resist. Still, some guidance on upsizing’s limitations would help me make a rational as opposed to impulsive decision.

Many thanks

Alan
Alan Shaw
Brisbane, Australia
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David Kilpatrick
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Re: Upsizing questions

Unread postby David Kilpatrick » Tue Oct 20, 2009 12:24 pm

If you start with the raw file, use Adobe Camera Raw and just select a larger size for the output. It interpolates directly from the Bayer pattern, and this produces a better result. You must remember that even a normal size output from any Bayer sensor is effectively being up-scaled relative to the colour resolution of the sensor - the D7D only has 1500 x 1000 of one colour of pixel, and the 2000 x 3000 is made up by taking a mix from 5 core pixels, 4 further peripheral pixels and in some raw converters some values from even more surrounding pixels (though these values don't add much).

A 17.5 megapixel output from Adobe Camera Raw can look very good from the D7D.

Interpolating up JPEGs is a different matter, you just blow up detail so it gets softer.

David

Alan Shaw
Acolyte
Posts: 22
Joined: Fri Aug 01, 2008 9:17 pm

Re: Upsizing questions

Unread postby Alan Shaw » Tue Oct 20, 2009 1:53 pm

David Kilpatrick wrote:
A 17.5 megapixel output from Adobe Camera Raw can look very good from the D7D.

Interpolating up JPEGs is a different matter, you just blow up detail so it gets softer.

David


OK, thanks David - I'd assumed that using JPEGs would be no good. But I'm still puzzled that if I can effectively upsize my 7D's RAW output to 17.5 megapixels, is this a substitute for using a camera with a higher megapixel count?

It sounds too easy!

Alan

David Kilpatrick
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Joined: Sat May 19, 2007 1:14 pm
Location: Kelso, Scotland
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Re: Upsizing questions

Unread postby David Kilpatrick » Tue Oct 20, 2009 5:22 pm

It is not a substitute - if you want really sharp images, downsize an Alpha 900 to 17.5 megapixels! But the D7D will produce pictures much sharper than you think, if combined with a high quality lens. Lens and focusing have more effect on final detail levels than the upscaling process.

David


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