I did some image converting, 25%, 50% and 75% and noticed that reduction to 75% in fact resulted in a larger file size, though dimensions show smaller sizes indeed.
Am not an expert, no doubt there is an explanation for it?
Same goes more or less for reduction to 50%
I would expect a file of 2.6MB would then be around somewhere between 1.2-1.5MB
Vainly tried to find an earlier thread on this matter, though probably there is.
You have the jpg quality set to 100%. The original would be lower than that.
Are you looking to make a lower resolution, or smaller size?
Thanks. A smaller size is the intention.
Not sure about the 100% quality thing though.
I didn't touch that whilst hoping the quality of the reduced files would still be 'as best as possible', even though, admittedly, it would be reduced due to the conversion.
There is no way to know what the compression quality was set to when the JPEG was created originally.
If you recompress a JPEG, you're taking the image data the JPEG decoded to and compressing that as a new file, using whatever quality settings you specify. That could result in a larger file due to that image data being more noisy (JPEG adds noise, and you then try to compress that noise which is harder to compress than the original) and using a higher quality setting than was originally used (100% quality usually produces much larger files as it tries to preserve more details).
Try 75% quality or so. That's usually a good compromise between image quality and file size, and will give you much smaller files than a lot of digital cameras output.
You shouldn't need to resize the image if you just want to reduce file size by dropping the JPEG compression quality. But if you aren't resizing the image, and it's already in JPEG format, then you may need to add the NOLOSSLESS argument to your Image CONVERT command to tell it you really want to recompress the JPEG without changing anything else (size, rotation, etc.).
Normally, without the NOLOSSLESS argument, Opus will try to avoid recompressing JPEGs if nothing else is changing, as doing so reduces the quality of the images. Sometimes you want to reduce the quality of the images (to reduce the file sizes), which is what the NOLOSSLESS argument is for.
(Edit: I should add that rotation can often be done without recompressing the JPEG file, and Opus does that when possible, unless NOLOSSLESS is specified.)
Once you have selected your resolution and compression rate and your modified file has been created. You can also reduce the jpg file size without any noticeable quality loss using a third party tool to re-process the image.
From another post.
There is a tool call Jpeg Archive , that will recompress a jpeg optimising the compression without reducing the quality. In my experience you can expect a 30% reduction is file size.
The link above explains how it does this, but the short version is. Jpeg is compressed in blocks using a consistent compression rate to each block. This tool (when using the smallfry flag) recompresses each bock separately, increasing the compression rate until it starts to see noise.
The result is the file looks the same but its smaller in size.
This is the button I use
<?xml version="1.0"?>
<button backcol="none" display="both" textcol="none">
<label>Compress image smallfry</label>
<tip>jpeg-recompress image smallfry</tip>
<icon1>#newcommand</icon1>
<function type="batch">
<instruction>"C:\tools\jpeg-archive\jpeg-recompress.exe" --method smallfry "{file}" "{file}"</instruction>
</function>
</button>
Both, thank you very much for the replies.
Truly appreciated.
My aim was to reduce the file in a sense that it would still display fairly large. I tried various methods and got puzzled about this increased size matter, hence my post.
I confess: instead of posting, I should have continued trying next following resize option, viz. "HD"
This gets me a reasonably large display/view (34x25cm on my display), whilst the file size is reduced by 50%, from 2.6MB to about 1.3MB. Probably the quality degraded, but I can't see it, so it is fine for me.
@wowbagger
Thanks for the link. However, Github is meant for developers, so I stay/stayed away from it: can't make head nor tail from the stuff there 