I have hesitated to post about this, but it seems to have become a strong trend lately so I thought I'd talk about it a bit.
I'm seeing a large number of image posts with extremely large file sizes, upwards of 2MB for a 1920x1080 image in many cases. This creates a burden on both our server storage and our server bandwidth. It makes images slower to download for all visitors. It seems to me that people are using extremely low compression/high quality settings to an unnecessary degree. Unfortunately server/web hosting space is not cheap and while we have upgraded our hardware over the years, we still have to deal with space limitations. We have increased the allowed file sizes per file and for the post as a whole several times over the years, but these needlessly large images are starting to take unnecessary advantage of these higher limitations.
I want to be very clear with what I mean when I'm saying "unnecessarily low compression/high quality" and "needlessly large images", because I imagine many of you may be thinking "Don't we want it to be as high quality as possible?". Like many things it's just not as simple as that.
First of all, it's well known than many applications include JPG output options that go to a level of quality/compression that is simply way more conservative than it needs to be. Photoshop and Lightroom are both notable examples (and both Adobe products, of course). If you do not use Save for Web in Photoshop, you almost always end up with a JPG that is larger than it needs to be. If you don't use Save for Web, you should never use quality settings higher than 9 or 10 at most. The slider goes up to 12, but these settings provide very low levels of compression and the results are literally indistinguishable from 9 or 10. Even when using Save for Web if you use the Maximum quality preset (or 100 Quality), you end up with a file that is bigger than one saved at 90 or 80, but is again visually indistinguishable. In other words you may get a 2MB JPG, but you could save a 1MB JPG of the same image at the same resolution that you would not be able to differentiate from the 2MB version, meaning that 1MB of space is "wasted" in that situation.
So I think for a large number of these situations people are just saving with the slider at max because they want best quality, but it's basically the same thing as setting TG render settings all to max. Yes, you will get the "best" possible quality, but you will waste render time in most cases, because lower settings work just as well (in a practical sense) to produce output quality that is visually indistinguishable from higher settings.
Another issue is people saving to PNG with Terragen images when that is basically never a good idea, unless you're posting to DeviantArt or something (and even then it's questionable except for print purposes IMO). PNG is great for simple line art, print, and other situations where there is not a lot of photographic-like detail. For Terragen images it just creates needlessly large images. Yes, it's lossless, and you may feel you want that, but in reality a well compressed JPG will give you results that you would be unable to differentiate from the PNG and at a smaller file size. So please avoid PNG for your TG images, at least when posting here.
I'd also like to advocate for a software option that I personally like a lot, it's free and is available on Windows as well as Mac and Linux: XnViewhttp://www.xnview.com/en/xnviewmp/
XnView is an extremely powerful image viewer and basic editor. It can read over 500 image formats and writes quite a lot of formats as well. Of particular relevance to this discussion is the Export function which has a very powerful JPG compression system that allows you to tune your compression to achieve the ideal file size and quality ratio. When you export an image to JPG you have a basic Quality slider and then a bunch of other options. I'll lay out my basic and recommended settings here and you can use them as a starting point and simply adjust the Quality slider and take a look at the Preview to see how it affects your image output quality and decide on a value for yourself.
For XnView JPG I use:
- Progressive: Enabled (this is optional, some people hate progressive)
- Optimize Huffman Table: Enabled (definitely do this)
- Remove all Metadata: Enabled (this is optional, but some metadata such as thumbnails can be quite large and contribute to your final file size)
- DCT Method: "Float (best but slowest)" (it's not very slow )
- Smoothing factor: 0
- Subsampling Factor: "1x1,1x1,1x1 (Best quality)"
I start with a quality of 90 for most images and that usually gets me a very reasonable file size and a very high quality. Sometimes I'll go as high 95 but I basically never need to use 100. Sometimes I'll go as low as 80 and get a much smaller file with still very high quality. I suggest leaving yours at 90 unless you really feel you need higher.
Take a look at the attached images for some comparisons of file size and quality. Basically XnView provides Photoshop-equivalent (or better) JPG compression for free. And for reference, the original image was a 4MB TIFF and a PNG version of this image was 3.2MB!
So please folks, help us conserve our server space and bandwidth. Use a little more compression/slightly lower quality and we all win!