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[Discussion] Resizing Pictures is harder than you think!

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 flvv

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發表於 2014-01-05 08:36 |顯示全部樓層
I used to think that even though the result of upscaling a picture might not be satisfying,  we should always get accurate picture downscaling a picture.

But is it correct?

Here is a simple test:





Make sure that your (image) browser doesn't scale them, and then reduce the height/width to 50%, and see what you got.

(You might want to save it first)

It should be quite obvious that you see different things if you're using windows.

I don't know about mac as I don't have one.

http://www.4p8.com/eric.brasseur/gamma.html

Here's a complete analysis discussing the problems in resizing pictures.

I was quite shocked after I read it.

After some testing, I realized that all the common web browsers don't do well, and even the professional software like photoshop don't, unless you use some tricks, which still makes the image lose details.

And this is what I found to solve the problem:

(I tested almost all the applications listed in the solution part but most of they either don't actually work, or is too complicated for common use.)

http://cpicture.thecloudsite.net/index.en.html

(Need to turn off sharpen picture for display)

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發表於 2014-01-05 12:12 |顯示全部樓層
me English no good cannot discuss.  me almost got no point of above.

me can read mass scales in pics, is it no good? am me getting blind of reading those pics

what to do then

Me no troll srsly

bump
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 flvv

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發表於 2014-01-05 16:04 |顯示全部樓層
0000000000 發表於 2014-01-05 12:12
me English no good cannot discuss.  me almost got no point of above.

me can read mass scales in pi ...


Basically when you try to upscale or downscale a picture, the result of common applications give you actually have incorrect color. The pictures that I posted were 2 extreme examples, so that you can easily see the difference.

If you can see only a grey block at the original size, you probably have problem with your monitor.
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跋山涉水的旅行者

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發表於 2014-01-06 12:32 |顯示全部樓層
I don't really get that.  I can see both "RULES" & "SUCK" in the first picture from whatever angel (light grey "Your scaling software RULES" in a heavy grey box, "SUCK" covers "RULE") which means my monitor has got a problem, right?
But what problem in detail how to fix it up?
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 flvv

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發表於 2014-01-06 13:58 |顯示全部樓層
本帖最後由 flvv 於 2014-01-06 14:22 編輯
0000000000 發表於 2014-01-06 12:32
I don't really get that.  I can see both "RULES" & "SUCK" in the first picture from whatever angel ( ...


In the first picture, you should see "Your scaling software RULES" very clearly at th original size.  The "sucks" can be seen, but hardly noticeable.

In the second picture, you should see a girl with yellow hair and green eyes clearly.

If you can't, that simply means that your monitor is of low quality.

There is no real way to fix it. You need to get a  better monitor, and do some calibration.

///

When you try to downscale them, most applications would show you " Your scaling software sucks" for the first picture and a grey block for the second one, which is incorrect.  


///



This is what you're expected to see (also the correct picture when you downscale to 50%...

The bigger the difference is, the worse your monitor is.

///



This is the result most scaling software would give you when you downscale them to 50%, which is totally different from the correct picture.

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發表於 2014-01-06 14:16 |顯示全部樓層
where you get this picture??
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 flvv

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發表於 2014-01-06 14:20 |顯示全部樓層
qmaniak 發表於 2014-01-06 14:16
where you get this picture??


I was just searching for a tool that might do well in upscaling, then I found some articles discussing this issue. (The one that I linked gives most details..
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發表於 2014-01-06 15:28 |顯示全部樓層
本帖最後由 qmaniak 於 2014-01-08 12:59 編輯

I don't know what software to create pictures like this.

Well, i can see the text in first picture "Your scaling software RULES" and "SUCKS" in covered. the text SUCKS which mean your system/monitor is low quality right?

example if your monitor set to low quality, the "RULES" will been seen "SUCKS" and the picture will show "Your scaling software SUCKS" which mean Your Computer is SUCKS

And in second picture i can see the girl were tied chains (maybe)
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發表於 2014-01-27 09:59 |顯示全部樓層
It's hard to collect HD HCG with a low volume。。。
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發表於 2014-03-05 05:04 |顯示全部樓層
Downscale use various algorithms (calculation methods).
The downscale image will look relatively normal if it use "near neighbor" method
It will turns gray with Lanczos or Gaussian. And their gray patterns are different too.
The image is probably designed to show algorithm problems, its not a monitor problem.

Downscale methods may vary on different platforms: browsers or software.
If your image software is good enough, it should allow you to choose which downscale algorithm to be used.
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 flvv

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發表於 2014-03-06 01:12 |顯示全部樓層
本帖最後由 flvv 於 2014-03-06 01:23 編輯
level3 發表於 2014-03-05 05:04
Downscale use various algorithms (calculation methods).
The downscale image will look relatively nor ...


Yeah, it's mostly an algorithm problem. It's just horrible that most algorithms have the same problem, while Nearest Neigbor isn't a good algorithm either.

On other pictures, the difference isn't so noticeable, but the resizing results are still wrong (either downscaling or upscaling).

---

The reason that the picture can show a monitor problem is a bit hard to describe.

It shows pretty different results on different monitors.

Basically on a cheap monitor, you can hardly see the girl as it should look very dark. It also differs if you look down or look up.

Only if you get a good monitor, the picture would look almost the same from different angles, which is similar to the 50% result.

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發表於 2014-04-11 11:10 |顯示全部樓層
Upscaling tends to not work well, but I can't tell much. Well, depends, if you're just scaling it a a smaller resolution like 5 or 10% bigger might not be that noticeable.
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發表於 2014-04-20 03:42 |顯示全部樓層
Yes, that's an inherent problem for scalar image. If you want better scaling use vector but it is harder to make "general" image using vector.
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