Author Topic: Very poor resizing quality  (Read 4581 times)

Offline devenh

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Very poor resizing quality
« on: September 30, 2007, 11:30:39 AM »
Perhaps I am doing something wrong, but the resizing performance of PM is significantly worse than Imagemagick (www.imagemagick.org).  Here's an example of a D2h jpg resized to fit in an 800x800 box using Imagemagick:



using these IM settings:

convert -auto-orient -resize 800x800 -unsharp 1x1 -quality 50

The file size id 86kb.

Now here is the PM resized photo to 106kb (using File | Save Photo as, quality setting is one up from the lowest):



So PM resizing results in a larger file of poorer quality.

Deven
« Last Edit: September 30, 2007, 11:39:47 AM by devenh »

Offline Hayo Baan

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Re: Very poor resizing quality
« Reply #1 on: September 30, 2007, 12:26:22 PM »
Though PM's ability in this area is currently not as flexible as you may want (if I am not mistaken this is going to change soon though).  However, having said that, I find it is more than adequate for web-publishing (have a look at my website for samples).
I too use the 1-from-the-lowest quality setting.  I do have the sharpening checkbox ticked as well though, and looking at your sample image you probably haven't.  I you indeed haven't, give it a try and see what it improves.
If this doesn't improve the output you may want to use IM until PM adds the improved controls.

Hope this helps
Hayo Baan - Photography
Web: www.hayobaan.nl

Offline FVlcek

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Re: Very poor resizing quality
« Reply #2 on: September 30, 2007, 02:09:58 PM »
Well, resizing really depends on what output you are seeking. I find PM to resize very well when it comes to transmitting photos back to my picturedesk, when I go from 12MP originals (edited in PS) to 2500-2000px wide files sent trough FTP. These are quite optimal, not oversharpened, so the picturedesk can easily sharpen them for final newspaper output at their given column size. That said, resizing for small web files is quite different, as these often need to be oversharpened unlike photos saved for later output to newspaper (no agency or picturedesk needs oversharpened photos). I suggest you wait for the implementation of finder sharpening controls in PM, because before that, if PM did sharpen more during save as/ftp, 99% of users would be _very_ unhappy because our files would be unacceptable by agency standards. You can't please everybody, and most people ftp the photos from PM to some other party which does later postprocess them on their own.

Just my two cents of rant, :)

Frantisek

Offline devenh

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Re: Very poor resizing quality
« Reply #3 on: September 30, 2007, 02:44:47 PM »
I don't see a sharpening option -- is this feature available on Windows 4.5.2?

Yes, my concern is web output.  I find PM files are lower quality and 25% larger.  I'd love to ditch IM and I hope PM improves!

Deven


Offline Kirk Baker

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Re: Very poor resizing quality
« Reply #4 on: September 30, 2007, 09:17:38 PM »
Deven,

I don't see a sharpening option -- is this feature available on Windows 4.5.2?

Yes, in the Export feature.  You can turn on sharpening.

Quote from: devenh
Yes, my concern is web output.  I find PM files are lower quality and 25% larger.  I'd love to ditch IM and I hope PM improves!

I looked at both of your images.  The IM version is definitely sharper than the PM version as can be expected since you had IM do sharpening.  But the PM version has better quality (less JPEG artifacting) than the IM version (look near the chin strap/cheek/water area).

You can get further compression by turning on the Subsample chroma checkbox but the quality will go down further.

Version 4.5.3 will have an option to sharpen in the Save as dialog.  It uses the same sharpening as the Exporter.

-Kirk

Offline devenh

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Export quality better
« Reply #5 on: October 01, 2007, 09:33:41 AM »
Okay, I tried resizing via the export function and got better results.

Here is the exported jpg with sharpening and set to the lowest quality level plus 1:



File size is 58kb.  Better than before, but still inferior to the IM image, but not surprising given the 28kb smaller file size.

Let's try at lowest quality plus 2:



Now the image quality is equivalent to (or better than?) IM, but the file size, at 104kb, is 28kb larger then IM, so IM is still more efficient.

Note, the reason this is important to me is that I have nearly 50k images online, so a 28kb size difference has a big impact on storage and bandwidth.

So my concerns are:

1. The "Save Photo as" function ought to have the same flexibility and output quality as the Export function.  Put another way, I should not have to use the Export function just to get the resized image quality I want.

2. It seems like the steps in the jpg quality selector are a bit steep at the low end.  The difference in file size between lowest quality plus1 and plus 2 is nearly 100%.

Deven

Offline Hayo Baan

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Re: Very poor resizing quality
« Reply #6 on: October 01, 2007, 01:12:20 PM »
Deven,

JPG compression is a non-deterministic "art".  Results are not necessarily the same between programs, not even when "comparable" settings are used. Even worse, what may give you adequate results on one type of image may give you bad results on another.  Thus, IM could give you better results now, but may give you worse results on different images.  Plus, for the web, how important is it that your 800x600 image is show perfect?  Not really, I'm thinking, otherwise you would use less compression in the first place.

Having said all that, maybe the compression algorithm PM uses would allow for some finer control (especially at the lower end).  If this is the case, maybe Kirk could implement this?

Cheers,
Hayo Baan - Photography
Web: www.hayobaan.nl