Interpolation

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Interpolation

Postby ATJ on Sat Jan 26, 2008 1:59 pm

I have been submitting photos to Alamy and one of their requirements is the files should be at least 48MB uncompressed (although you actually submit JPEG files). This means that even uncropped shots from the D300 have to be interpolated by at least 20% on each side to get an image which is at least 4899x3266 pixels. Shots from my D70 need at least 63% increase on each dimension.

I use CaptureNX and PaintShopPro 9 for my post processing, both of which allow for upsizing images. I tried all the resampling methods PSP9 provides and other than Pixel Resize and Weighted Average, I can't tell the difference between them and with CaptureNX. Interpolation has some samples. Are there some better methods out there (excluding PS plugins)? Are the ones I'm using good enough?
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Re: Interpolation

Postby Steffen on Sun Jan 27, 2008 12:27 am

ATJ wrote:I have been submitting photos to Alamy and one of their requirements is the files should be at least 48MB uncompressed (although you actually submit JPEG files). This means that even uncropped shots from the D300 have to be interpolated by at least 20% on each side to get an image which is at least 4899x3266 pixels. Shots from my D70 need at least 63% increase on each dimension.


The old problem that usually those people get to set parameters who don't understand them...

Just convert your images to 16-bit TIFF before submission and you should be fine as to the minimum file size.

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Re: Interpolation

Postby ATJ on Sun Jan 27, 2008 9:41 am

Steffen,

Steffen wrote:The old problem that usually those people get to set parameters who don't understand them...

Agreed.

Steffen wrote:Just convert your images to 16-bit TIFF before submission and you should be fine as to the minimum file size.

They only accept JPEG files. It is also not the file size as such as the JPEGs I'm submitting are between 2 and 4MB and getting them accepted.
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Re: Interpolation

Postby Blokeman on Sun Jan 27, 2008 5:39 pm

I don't pretend to understand the technical aspects of interpolation, but I use Genuine Fractals.
It seems to do the job ok, I save the raw as an 8 bit Tiff, upsize to 5200 px wide, this normally makes it around 51MB, and then save as a jpg quality 11.
If anyone has a better way I'd like to know it too..
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Re: Interpolation

Postby ATJ on Sun Jan 27, 2008 6:25 pm

Blokeman wrote:...but I use Genuine Fractals.

Which is a PS plug in.
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Re: Interpolation

Postby Blokeman on Sun Jan 27, 2008 6:58 pm

ATJ wrote:8<....(excluding PS plugins)?

Fair enough, missed that bit...
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Re: Interpolation

Postby Viz on Mon Jan 28, 2008 4:06 pm

I noticed in the back of the current photo trader that there was a tutorial extolling the virtues of doing the up-res via adobe camera raw (ACR) because it apparently draws on the extra green photosite available per pixel - I know you are excluding PS, but is there an up-res available at the raw conversion stage with PSP? I have used genuine fractals a fair bit, but I believe you are better extracting the extra data from the raw file, and at 16 bit to begin with, if possible.
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Re: Interpolation

Postby davo on Sun Feb 03, 2008 3:48 pm

Sorry to get in late on this discussion. Bicubic interpolation availbale thru PS will give you the best quailty (other than fractals which I have not seen in PS ? a plugin). Interpolation is a method used in up / down sizing or rotaing an image. In for example, upsizing, if you double the size, calculation of the new pixel value is easy. More difficult if you increase the size by 20%, the calculation needs to take into account the adjacent pixel values. Nearest neighbour method does exactly that, uses the nearest neighbouring pixel. Bi-linear uses the surrounding 4 pixels and "averages" their value, depending on how close they are. Bi-cubic uses the nearest 16 pixels. It gives the best estimate of what the new pixel value, if it was originally captured at that increased resolution, compared to the other methods discussed.
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