English > Feature Suggestions

Image scaling/resize quality

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nostra:

--- Quote ---A user setting to control JPG image quality would seem a simple fix.
--- End quote ---

all images are saved as they are without converting to jpg or changing the compression level.

Hyomil:

--- Quote from: rick.ca on May 05, 2010, 11:52:56 am ---Sorry, I don't understand. I find it very difficult to tell the difference. In the attached, I can see the lettering at the top is noticeably different—at full size. But the PVD version looks better!

--- End quote ---

Just to make sure, you understood that the PVD version is the one on the right--not the one on the left? ;)  Since I saw the difference even in the PNG PrintScreen cap as well as when using PVD, I thought it couldn't be something wrong with my system.  And I still see the sharpness difference clearly even in your JPG, although that has more pixelation/noise than my PNG did, which I presume is a result of the JPEG compression and would make the 'smoothness' of the PVD version appear 'better.'  If that noise is not from the JPEG compression and you see it even in the uncompressed version of that image, I'm at a loss to explain it unless its a byproduct of the program you did the resizing with.

But maybe it could be due to a difference between an LCD monitor and a CRT like the one I'm using, as I know fonts that look good on one can look bad on the other (ex. ClearType), although I thought the difference with photos was minimal.  Is everyone else using an LCD?  (I still prefer CRTs over LCDs or plasmas, as AFAIK only OLEDs or micromirror projectors can match/better their response times.)

Another thing I thought of, assuming the difference is in the way PVD scales the image vs. my display, is that some kind of deliberate noise reduction has been incorporated into the algorithm which might make poor-quality images look better when enlarged but high-quality images look worse when reduced.  (Photoshop has a different algorithm for enlarging images than it does for reducing them--Bicubic Smoother vs. Bicubic Sharper, respectively.)


--- Quote from: buah on May 05, 2010, 11:54:52 am ---And for whom is this thumb down? ;)

I'm kidding, of course, just couldn't stand not to notice...

--- End quote ---

In my mind, it was thumbs down for having to crop the image to fit the 512K attachment size limit of the forum.  The full PrintScreen image was 1280x960 and too big when compressed using the lossless PNG format, which I needed in this case.  And thumbs down to the movie too--I saved the poster as a reminder not to watch, lest I should forget.   ;D

buah:
My thoughts what could be the reasons for (not) seeing differences:
- Different types of monitors we're using
- Different resolutions we're using
- Differences in (default) image viewers themselves - like video players: different picture frame quality with different players.

Hyomil:

--- Quote from: buah on May 05, 2010, 08:51:26 pm ---My thoughts what could be the reasons for (not) seeing differences:
- Different types of monitors we're using
- Different resolutions we're using
--- End quote ---

Yes, LCD monitors have a native resolution (like 1280x1024) and if you use any resolution other than that, the picture will be significantly less sharp.  CRTs don't have that problem, and I tested mine by viewing the image at different resolutions.  If you have an LCD, I would think you'd want to be using its native resolution, although I don't have any personal experience with it.


--- Quote ---- Differences in (default) image viewers themselves - like video players: different picture frame quality with different players.

--- End quote ---

(For those who aren't aware, you can view forum image attachments in your browser by clicking on the image thumbnail rather than downloading it by clicking on the attachment name.)

Differences in scaling algorithms between image viewers, yes, but you'd want to view the image at full/actual size and there should be little, if any, difference there.  I checked the images in Photoshop, FastStone MaxView, and MS Paint with identical results.

rick.ca:

--- Quote ---And I still see the sharpness difference clearly even in your JPG, although that has more pixelation/noise than my PNG did, which I presume is a result of the JPEG compression and would make the 'smoothness' of the PVD version appear 'better.'
--- End quote ---

I did have to use JPG (at 95%, I believe) to get it less than 512k. I thought it still conveyed the same difference I saw in the originals. Those too, were resized a little to display at the same size in the two different viewers. I use an LCD at native resolution. But whatever you call the affect and regardless of what causes it, I still wonder what difference it makes. This just shows how subjective this is. I happen to think the image you believe is somehow "degraded" looks "better" than the original. Had my attention not been directed to making the comparison, I would never notice the difference.

So the question is, considering PVD is not Photoshop, is there some issue with how it's handling images? I don't know how these things work, but I would assume the requirement is so common these things are handled in an acceptable manner by standard tools—that don't require the programmer to be an imagining expert. Is my assumption incorrect? If not, maybe some research on available tools and the best way to implement them would be helpful. :-\

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