Batch convert to rename reduces file size

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ydb
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Joined: Mon May 08, 2017 4:50 pm

Batch convert to rename reduces file size

Postby ydb » Mon May 08, 2017 4:55 pm

Hello, I am trying to use batch convert to rename files using EXIF data. The problem is that the file size reduces (not definition). So I suppose there is quality loss.

I know I could use batch rename for this, but convert is more flexible, because it allows output directory selection.

Thanks for your help.

Yves

cday
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Re: Batch convert to rename reduces size

Postby cday » Mon May 08, 2017 5:14 pm

ydb wrote:I am trying to use batch convert to rename files using EXIF data. The problem is that the file size reduces (not definition). So I suppose there is quality loss.

I know I could use batch rename for this, but convert is more flexible, because it allows output directory selection.

On the Output tab, are you setting the compression level used when the files are saved using the Settings... button below the Format button?

There is no reason why the file size should be reduced if you use similar compression...

If you are renaming JPEG files, there is a Settings... option 'Use estimated quality (when possible)' option.

ydb
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Joined: Mon May 08, 2017 4:50 pm

Re: Batch convert to rename reduces size

Postby ydb » Mon May 08, 2017 7:39 pm

I am using format "same as original", so "settings" button is greyed.

cday
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Re: Batch convert to rename reduces size

Postby cday » Mon May 08, 2017 7:46 pm

ydb wrote:I am using format "same as original", so "settings" button is greyed.

That's interesting, and I don't immediately have an explanation as logically one might wish to save to the same format but also change the compression level or another setting...

But you should be able to set the actual file format required, and then set a desired compression level?

ydb
Posts: 3
Joined: Mon May 08, 2017 4:50 pm

Re: Batch convert to rename reduces size

Postby ydb » Mon May 08, 2017 7:48 pm

I have tried that, and checked 'Use estimated quality (when possible)', but then the file is bigger.

cday
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Re: Batch convert to rename reduces size

Postby cday » Mon May 08, 2017 8:07 pm

ydb wrote:I have tried that, and checked 'Use estimated quality (when possible)', but then the file is bigger.

Well, maybe it is a case where it isn't possible to estimate the quality level of the input files??

If filesize is important, you still have the option to set and test different quality values, and you might possibly find that surprisingly low settings provide both small file sizes and acceptable quality, depending on your use case... Note that quality setting values in one program cannot, in general, be equated with quality values in other programs.

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helmut
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Re: Batch convert to rename reduces size

Postby helmut » Tue May 09, 2017 12:02 am

ydb wrote:... I know I could use batch rename for this, but convert is more flexible, because it allows output directory selection.
Using batch conversion for batch renaming is an unusual but possible way.

But:
- Slow performance
Batch rename renames files, only, while batch conversion loads every image, applies a transformation/action (no transformation/action in your case) and saves the image with a new filename, again. So Batch conversion does a whole lot more than Batch rename and is very slow compared to batch rename.

- Worse image quality or larger file size with every JPEG compression
In respect of image quality this works fine for image formats with lossless compression (PNG, GIF, ...), only. For formats with lossy compression like JPEG your images will loose some quality with every compression. I.e. your compressed JPEG images will be uncompressed and compressed lossy, again. When compressing XnView doesn't know which details belong to the original image and which details are artefacts from a previous compression. XnView can estimate the previous JPEG quality but it's very unlikely that the new JPEG compression uses the exactly same parameters and 100% same algorithm as the previous compression. Therefore when resaving a JPEG file its file size may decrease or increase and image quality might remain about the same or get worse (it will never get better) depending on your JPEG quality settings.

Some links (search for "resaving JPEG") which show samples and perhaps explain it even better:
https://petapixel.com/2010/02/04/saving ... -of-times/
http://www.impulseadventure.com/photo/j ... aving.html

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m.Th.
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Re: Batch convert to rename reduces file size

Postby m.Th. » Tue May 09, 2017 3:28 pm

For what you want you can use Import and Sort - much faster.

Steps:

If you want to rename & copy the actual folder then:
1. Copy from Address Bar the actual folder
2. Start the Import & Sort dialog
3. Paste the actual folder in Source field.

If not, just start the Import & Sort dialog.
The last folders will appear in Source and Destination fields. Handy when you want to download images from cards. :) (...perhaps this is your usage case...)

4. uncheck „Subfolder” field.
5. check „New filename” field.

Enjoy!
m. Th.

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