Not sure if this is OT, if so, please feel free to delete my post.
I’m just curious to hear what other people use to compress their jpgs.
I want to keep the EXIF info when I post to Flickr or on my website, but I also want to reduce the file size.
Right now I’m using Irfan View with the RIOT plugin and it seems to work fairly well, but I wonder if you have better solutions.
Thanks for any info.
Andrew
There are a few threads out there. From the top of my mind: Preparing image for Facebook. If it doesn’t help, just use the search tool.
Thank you, afre, I’ll take a look.
I just use what ever darktable uses on export and I am happy with it.
Yeah, basically all apps have an image quality or compression slider or box that you could adjust, and also a file compression setting. The thing to watch out for is that the image quality number can vary great from app to app. So 90 on app A might be 80 on app B. Be sure to make the image quality and file size comparison yourself!
A dedicated program usually shows a preview of how much degradation will be applied to the image, which is extremely handy. I need to export for web and the preview is definitely important. Without the preview I have to export, check the result, the file size, and then re-export again if I’m not happy. This can takes several rounds until I’m satisfied with the result. If there are several images to export it’s going to be a lot of time.
I’ll stick to RIOT for the time being, it’s doing the job OK. Just thought there could be some other nice utility I could be missing.
I use the standard stuff. JPG size comes from two things: somethiing akin to dropping decimals (which is the “quality”), and chroma subsampling. The latter means that the image is split into three channels: one luminosity channel and two ‘color’ channels, and the color channels are scaled down. When decompressing, they are of course scaled up. Our eyes being much more sensitive to luminosity than to color, we barely notice it.
The chroma images can have either the size of the luminosity image (no chroma), half the size (compressed 1:2 in one direction only), or a quarter of the size (1:2 compression in both directions). This is where the biggest size gains come from: with full chroma, you have X+X+X (3X) pixels to compress, with half-chroma you have X+.5X+.5X (2X), and with quarter-chroma you have X+.25X+.25X (1.5X). Some JPEG compressors have no distinct controls, and link the chroma subsampling to the quality.
Thank you, ofnuts.
I realized after I posted that I omitted another important feature, which I’m glad you pointed out.
A shareware jpg compressor I tried a while back, can’t remember the name right now, had in fact controls to tweak the amount of compression for chroma. Not only, there were also slider for shadows, mid tones and highlights which were handy depending on the image I was converting.
I forgot to mention that GIMP has all these features.
