Opus JPG conversion quality

I'm no image format aficionado or anything so I have a question about relative image quality between the formats Opus allows conversion from/to... I get that JPG is a 'lossy' compression format, and have started converting to PNG inside Opus for smaller size and good quality, since converting to JPG produces noticeable loss of quality. But then again, my digital camera (Nikon CoolPix 4600) takes it's pics in JPG format and they look great. Are not all JPG compression engines equal, and is the one used by Opus on the 'low end'? Just curious... I know there are a fair amount of you using Opus who also work alot with images, and so was hoping someone could comment since I know little about the subject.

Opus uses one of the standard JPEG libraries that's probably used in a lot of stuff. I know that by default Opus produces JPEGs with a lot more artifacts than other programs, but you can increase the quality setting that is used:


I haven't done any tests to see if, given a file-size target, Opus creates better or worse images compared to other programs. Has anyone done this and got some results?

I wouldn't expect Opus to do as good a job as Photoshop's, a decidated art program that cost me £500, but it would be strange if it was producing worse results than other programs which use the same library (and my bet is that's most of them).

Of course you can hook other converters (e.g. ImageMagick which is free) into Opus but then you lose the nice, integrated progress dialogs and file-replace and error handling that you get for free with internal Opus functions.

Hi Steje,
I'm not certain why you're attempting a smaller file size that still has good quality.
If it's an attempt to produce a high quality image for your web site that is of a smaller byte size, I can help with jpg images.

If you write me privately, I'll show you a method of compressing selected areas of your photo at different jpg compression qualities ( not freeware ). I'd be glad to process a few samples for you.

I also have some freeware Jpg2000 and Lurawave tools that produce excellent results.

:opusicon: porcupine

Thanks guys... I wasn't really looking to 'solve a problem' so much as just had some curiosity about it since noticing a while back that the quality of a simple bitmap I had been editing for my website banner looked like crap after converting to JPG. I had since realized that JPG was a 'lossy' compression format... and I've always only ever used quality=100 when converting bmp to jpg but still noticed the obvious difference in quality from the original bitmaps. I was just wondering if anyone knew why things like digital camera pictures look so great if JPG is an inherently 'low quality' format. Though now I think back on it - alot of the posts I've read from Porc and JohnZ refer to RAW format and such...

Yes Steje,
I don't know all the whys, but these kind of things turn out extremely well in png's.
An image of text in a web unfamiliar font for instance.
PNG's allow you to specify to some extent the number of colors in the resultant image.
The result is crisp , clear and of small file size.

Photos are a different story.
I can do better than PNGs with JPGs, both in image quality and filesize.

:opusicon: Porcupine

For me the scale seems to be off in Opus when it does the conversions.

I have to raise the quality factor (I pretty much always do JPG conversions) by a factor of at least 10 as compared to the Photoshop.

When I do that the overall file size is comparable to the Photoshop.

In other words, roughly speaking, a Photoshop jpg conversion at 40% is about the same in quality and file size as an Opus conversion at 50-60%.