Question for Iliah about interpolation software

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DirkVermeirre
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Question for Iliah about interpolation software

Post by DirkVermeirre »

Hello Iliah,

Great to see you here, I remember that I always was reading your posts on Dpreview with great interest. I have question for you Iliah and hope that you can help me. I searched on the web to find interpolation software or filters for a specific kind of images and couldn't find one that worked. In my sea series I have several images that are quite blurred and have subtle color tones and almost no detail and all what I tried until today doesn't do a good job with that kind of images. I guess that the algorithms are not suited for such images and are only working well with normal images. To print them at bigger sizes the best result comes from no interpolation at all and that means with a much lower dpi then normal. A gallerist asked me for even a lot bigger sizes (2 meters and more) I'm afraid that the dpi will lower to much without interpolation and that's why I'm searching something that could work for these images. Do you perhaps know something that could do the job ? I tried all the possible modes and settings in Photoshop, Genuine Fractals and some other, all with very bad results compared to the non interpolated prints.

With kind regards,

Dirk Vermeirre
Iliah Borg
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Re: Question for Iliah about interpolation software

Post by Iliah Borg »

Dear Dirk,

This is a very interesting challenge. As you know, an image from digital camera comes through the first round of interpolation when it is converted from raw. It happens that this first round of interpolation comes to interference with the second /upsize/ interpolation. The easiest thing to try would be taking Lab representation of conversion and scaling L channel separately from colour channels with different algorithms, while applying the certain amount of blur to colour channels. Also, have you tried http://www.ddisoftware.com/qimage/ ? If both things are not providing you with the results you need please let me see a couple of raw files.
DirkVermeirre
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Posts: 50
Joined: Fri 29 Aug 2008 01:02

Re: Question for Iliah about interpolation software

Post by DirkVermeirre »

This is a very interesting challenge. As you know, an image from digital camera comes through the first round of interpolation when it is converted from raw. It happens that this first round of interpolation comes to interference with the second /upsize/ interpolation. The easiest thing to try would be taking Lab representation of conversion and scaling L channel separately from colour channels with different algorithms, while applying the certain amount of blur to colour channels. Also, have you tried http://www.ddisoftware.com/qimage/ ? If both things are not providing you with the results you need please let me see a couple of raw files.
Iliah Borg
Dear Iliah,

Thanks a lot for helping me with this problem. Indeed. My problem is the upsize interpolation. The software seems to get confused with such images and don't know which pixels to use for upsizing and that results in smeared ugly parts in the images in some areas. In the series I have images made with the Fuji S3, Nikon D2x (100 or 200 Iso) and the 5D and 5DII. With the Fuji and the Nikon I didn't have raw files as the jpg's were (at that time) good enough for me. I only started shooting Raw with the Canons.
Is there a raw converter (I'm using DPP) that can export the images in thee Lab modus ? Or do I have to convert the 16 bit Tif files to Lab in Photoshop ? It's not clear to me how I could convert the channels separately in Lab. Do I have to split channels and recombine them after having resized them all separately ? And what to do for those for which I don't have raw files Iliah ?

No I didn't and saw that it's only for PC and I only have Macs. How can I provide you raw files Iliah (I don't have your email address).

Thanks a lot for taking time to my problem, I really appreciate that Iliah.

Warm regards,

Dirk
Iliah Borg
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Re: Question for Iliah about interpolation software

Post by Iliah Borg »

If you have problems with upsize, you can apply sharpening before upsizing. Depending on the image, 200/1/10 or 350/.3/0. There is no need to apply sharpening to colour channels, sharpening colour channels has detrimental effect to the image most of the times (there is one important case when it is not - but I feel at this stage discussing it will only mud your research). Convert the image to "16 bit", then to Lab and apply sharpening to L channel only (select it in the Channels or do the split, it is even better). Next, upsize using Bicubic Sharper, contrary to what Adobe are recommending. Sometimes pre-sharpening is not needed at all when upsizing is done via bicubic sharper. Upsizing, set the resolution to the number higher than you need for the print. If the print is done at 150 ppi (usual for wall prints), set the resolution to 227. Next downsize to the resulting resolution, again using bicubic sharper. INk will smear a little, so judging the result at 50% magnification should be adequate. Colour channels can be upsized in a single move, using normal bicubic. Next, re-join the channels and convert to the destination colour space.

The only converter that works in Lab mode is RPP.

My e-mail is ib@pochtar.com , or - I can setup an FTP account for you if you prefer.
DirkVermeirre
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Joined: Fri 29 Aug 2008 01:02

Re: Question for Iliah about interpolation software

Post by DirkVermeirre »

Dear Iliah,

Thanks very much, this method sounds incredibly good and logical. I just tried with an image and I must say that on screen it looks like the best version I made with interpolation. But I need to let make prints to judge the results as a screen is something completely different then a print. Until now the best results came from Lambda prints, they were better then those from inkjet printers (Epson and HP). With the inkjet the differences were quite big depending on the used papers. I remember from longer time ago when I needed to prepare a lot of files for offset printing and I was using Binuscan Pro from Monaco that the files in cmyk looked horrible on the screen but were absolute top quality when printed.
Fantastic that you can help me with this Iliah and I will send you a few files with YouSendIt one of these days (I'm quite busy for the moment), thanks in advance for putting so much time in it.

With kind regards,

Dirk
Iliah Borg
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Joined: Tue 16 Feb 2010 17:53

Re: Question for Iliah about interpolation software

Post by Iliah Borg »

Dear Dirk,

The amount of sharpening depends on the printer you are going to be using. I usually print crops applying different amounts of sharpening, to get some correlation between what I see on the screen and how it prints on the printer.
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