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Author Topic: JPG Compression Bug in version 4.12.0  (Read 352 times)

Mav99

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JPG Compression Bug in version 4.12.0
« on: July 26, 2015, 07:03:20 AM »
There seems to be a bug with JPG compression. Automatic saving as well as saving from the editor correctly uses the quality setting from Options/Image File Format. But using "Safe Image As..." from the Prompt dialog saves the jpg with default quality.

There also seems to be no way to set JPG quality directly while saving. Help suggests a quality option in the file-save dialog but in version 4.12.0 that's nowhere to be found. There's only the image preview added to the file-select box. (I'm using Windows 7 x64 Ultimate)


And while we're at it, some suggestions:
The quality setting seems very coarse. With the capture I used for testing max quality at ~380kb is fine, the next lower setting at ~ 150kb already shows significant compression artifacts. Everything below that is completely useless. It seems the quality below 100% is worse than in every other program I know. Unless that's a bug, there should be more options between 100% and the next lower setting.
 
Also showing a percentage for the quality, like 100%, 90%, 80%, 75% would be helpful.


Other than that, great program!


mouser

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Re: JPG Compression Bug in version 4.12.0
« Reply #1 on: July 26, 2015, 10:49:49 AM »
Hi Mav,

Thanks for your clear comments.  Sounds like I must have lost the Save As quality option somewhere along the line -- I will try to put it back, and make sure it defaults to the option set in the configuration.
And i'll have a look at the quality setting range -- maybe i can tweak it.

ps. You probably know that screenshots should almost never be saved in jpg format -- that png is going to be more appropriate in almost every case.

Mav99

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Re: JPG Compression Bug in version 4.12.0
« Reply #2 on: July 26, 2015, 02:20:44 PM »
Thanks for your clear comments.  Sounds like I must have lost the Save As quality option somewhere along the line -- I will try to put it back, and make sure it defaults to the option set in the configuration.
Great.

And i'll have a look at the quality setting range -- maybe i can tweak it.
I did a few more tests. Min compression/Max quality is fine. The next step looks already like 7/8 of 12 in Photoshop or about ~70/75% in most other programs. One more step and you're at about 60% quality compared to other programs. After that the steps seem to get smaller and smaller. With 10 steps on the quality slider I somehow expected linear 10% or smaller steps from min to max compression.

ps. You probably know that screenshots should almost never be saved in jpg format -- that png is going to be more appropriate in almost every case.
I'd say that depends on the content. I was capturing video previews from a website. These screenshots contain a little text and multiple images (which are medium quality JPGs to begin with). Compared to max quality JPG the PNGs are 4 to 5 times bigger with no visible difference in quality. PNG makes no sense here.

Also, to post screenshots of something in a forum, for example to explain or discuss software features, PNG is often unnecessary as well.
I usually only use PNG when it's smaller or when quality is more important than size.

(I guess I spent just too much time optimizing website images for size to keep mobile users with limited bandwidth and volume happy  ;))



mouser

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Re: JPG Compression Bug in version 4.12.0
« Reply #3 on: July 26, 2015, 04:08:59 PM »
As I suspected from your post, you are familiar enough with image formats to know when to use each  :up:
I can't really disagree with anything you've said -- though for a non-mobile forum post i would always go with png.