Jpg compression level conversion

[bugmenot]

Is there a method to adjust JPG compression level during image conversion? I'm having problem where images converted using ExifTool appear slightly overexposed compared to those processed with Nikon ViewNX. Does ExifTool offer a feature to regulate compression settings? Some applications, like JPEG Compressor, automatically adjust JPG compression level to maintain image quality consistency. Thank you.

[greybeard]

What do you mean by image conversion? Can you show which command you are using?

Have you found that compression level affects exposure?

[bugmenot]

Hey hi @graybeard, thank you for your response. I use exiftool -all= -tagsfromfile @ -all:all -unsafe -m -q -q <filename>. And yes, I've noticed that adjusting the compression level seem to impact the exposure slightly.

[greybeard]

I'm not sure what you are trying to do - according to the documentation that command is used to fix corrupted metadata - its not going to convert the image.

Maybe I'm confused and Phil will correct my understanding.

[Phil Harvey]

We should be clear the ExifTool does not perform image conversion, so it can not affect the JPG compression level or the image data itself.  ExifTool deals only with metadata.

- Phil

[StarGeek]

Is there a method to adjust JPG compression level during image conversion?

Exiftool doesn't have the ability to do conversions or compression.  It doesn't touch the actual image data, just the metadata. If you compare the raw image data between two images with a program such as ImageMagick with a command like
magick compare Original.jpg converted.jpg x.png
they will be identical. See FAQ #13c, How does editing a file with ExifTool affect image quality?

I'm having problem where images converted using [ExifTool appear slightly overexposed compared to those processed with Nikon ViewNX.

I believe the command you listed removes all color data, such as ICC_Profiles. Try adding -ColorSpaceTags after the @ sign.

Otherwise, can you provide a sample image that exhibits this behavior.