Options->Read/Write->JPG: Use estimated Quality

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negg
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Options->Read/Write->JPG: Use estimated Quality

Post by negg »

Searched forums and help for "estimated", but could not find anything...anybody knows what that checkbox is for?

Options->Read/Write->JPEG: Use estimated Quality if possible

negg
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Clo
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For thumb nails ?

Post by Clo »

—> negg

:) Hello !

• Hm… I've to admit that I've not any precise information about this… :?

• However, since that box is in a group about the thumb nails for JPEG, one could suppose that's related to …

- In other words, I guess that XnView estimates quickly the quality of the JPEG with regard to the ratio
size (pixels)¦size (Bytes)…maybe the number of colours too (?), then displays the thumb nail for it according to this parsing…
- Perhaps the EXIF info (if present) is considered.
- But I don't see the reason for the “…if possible:?:

• It's not obvious to watch a difference for the same image thumb nail with¦out this option,
but it should need to test a lot of various JPEG images to get a clue…

• I hope that Pierre'll give us more details, so then we'll add a note in our Manual, to report in the official Help too…

:mrgreen: VG
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Re: Options->Read/Write->JPG: Use estimated Quality

Post by xnview »

negg wrote:Searched forums and help for "estimated", but could not find anything...anybody knows what that checkbox is for?

Options->Read/Write->JPEG: Use estimated Quality if possible

negg
When the jpeg is loaded, an estimate original quality is computed, so if that is checked, i use this quality as output
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Clo
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for 2 ?

Post by Clo »

:arrow: Pierre

:) Hello !

• Thank you, but which quality is it used for the thumb nail ?
- This estimated one, or else (the quality chosen in the options, or maybe the embedded thumb nail has another quality) ?
- How is it rebuilt (if done), I mean in which quality when the box is ticked ?

:mrgreen: KR
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negg
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Re: Options->Read/Write->JPG: Use estimated Quality

Post by negg »

xnview wrote:
negg wrote:Searched forums and help for "estimated", but could not find anything...anybody knows what that checkbox is for?

Options->Read/Write->JPEG: Use estimated Quality if possible

negg
When the jpeg is loaded, an estimate original quality is computed, so if that is checked, i use this quality as output
Thanks Pierre for making this clear, but errm...here this simply makes no difference. I took a digital camera photo with 4 MB and set the JPG quality to 75. It makes no difference if I check "estimated qual." on or off, the jpg is 450 kB afterwards all the time.

Am I getting something wrong? What factors does it depend on if an estimation is "possible" or not?
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When?

Post by Clo »

—> negg

:) Hello !
…What factors does it depend on if an estimation is "possible" or not?
• Right, that's the point !

- As well for that as for the thumb nail, we don't know still…

- We added the JPEG writing options in our Manual, but this is not quite satisfactory, these points are missing…
…It makes no difference if I check "estimated qual." on or off…
• Yes, I noticed that above, but like I said, it's worth to test more…

:mrgreen: KR
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Post by Drahken »

If you set the slider lower than the original quality, that will override the estimated quality. Estimated quality only takes effect if you set the quality significanly higher than the original image. Do this:

Open the lower quality copy you made, check the estimated quality box, then set the quality slider to 98~100 and save it. Now repeat, but uncheck the estimated quality box (keep the slider at 98~100). Now compare the 3 images. You will see that the estimated quality one will be much closer to the original than the non-estimated one (although it'll probably still be larger). In my case, the original was 402k, the one with 98/estimated was 449k, while the non-estimated one (in which all other settings were the same) was 626k.
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Re: Options->Read/Write->JPG: Use estimated Quality

Post by Janis »

I had the same problem understanding this option. I would suggest to add word "original" there: "Use estimated original quality if possible" or "Use estimated quality of the original if possible". Or add it as a tooltip if it's too long. Or at least add the explanation to the user's guide (F1).