MatthewK wrote in post #17982701
Pekka: I wasn't aware of a lot of those things... where exactly are these tips posted on the forum to help us insufferable noobs find the way? After searching, I didn't seem to be able to find any FAQ or anything (which I proclaimed in the opening sentence in this thread). I didn't make this thread as an indictment of the quality of the forum: far from it! I've been coming here for years, and absolutely love what POTN has evolved into. I just want to be able to best put to use the resources available, and on this particular topic I didn't see any guidance.
Sorry if the information has been elusive. I have expressed earlier that image quality of uploads is very good, and I have not seen need to make a detailed explanation of it.
I use 16-bit Imagemagick for manipulating uploaded photos, and to make thumbnails. The process is quite simple:
- if image is within current forum limits, it is only re-saved as JPEG with 80% compression.
- if image is over the limit, it is scaled down (with sharpening) and then saved as JPEG with 80% compression.
Images are never scaled up.
The process is identical for every upload. There are no changing variables to quality.
Resampling process is based on work by Nicolas Robidoux in http://www.imagemagick.org …ilter/nicolas/#downsample
I use his proposition code
"-filter LanczosRadius -define filter:blur=0.88549061701764 -resize XxY"
Earlier, I used linear color space and then converted to sRGB, but that messed up some images (b&w), so this is now done on the original color space until I find solution to that problem. Without color conversions the process is very much faster, which is also a goal.
Images retain EXIF and color profile info. Thumbnails are stripped from them: a known problem is that AdobeRGB images get sRGB thumbs (pale colors).
The purpose of sharpening is not to make "wow, look how sharp it is" effect. It is there only to remedy the resampling blur and not affect ISO noise or make assumptions that member wants images really sharp.
Even if images are scanned for malware, the re-save step is there to both save server recources and to prevent malicious code in originals passed to members. I have come to 80% compression by carefully comparing what is the best balance between excellent quality and file size. Now resulting file sizes are about 250kb for a 1280 image, the size can grown bigger with noisy images and complex images, smaller with simple images.
Some images I've uploaded come out just fine and look great, yet others just lack the detail and appear smudged or aren't sharp at all. For example, the flower in this post looks horrible, yet on my Mac it's razor sharp. I tried numerous export methods to try and get it to somewhat resemble the original, but haven't been able to get it there:
https://photography-on-the.net …showthread.php?p=17980135Sharpening needs a certain contrast difference to be applied. That image does not have much of those. To me it looks, fine, the center of the flower is sharp. Again, the premise is to keep the look of the original intact - such aggressive sharpening of low luminance differences would ruin the image.
It's also sort of frustrating when you see someone post a nice, crisp, brilliant image, and then I post something that just pales in comparison but looks 10000x better in my Lightroom, and I can't get that to display properly. I know I don't take anything special compared to most photographers on here, but I at least want to show what I have accomplished in the best way possible.
You will see the image better in lightroom because the display output in Lightroom is sharpened for you and, if the color space is other than sRGB, you will see deeper colors and maybe better contrast.
To view an image full screen in Lightroom is not same as viewing image full screen in browser. For a meaningful comparison you need to save the image in (longer side) 1280 sRGB JPEG and then compare it to uploaded image in 100% view, in 100% zoom in browser. To save the uploaded image from POTN to your disk, click the glasses icon, right click the image and save to disk. Rename the .duck file extension to .jpg or .jpeg. You can then drop them both to two browser tabs, and switch tabs to see all the minute differences.
I think there are a couple of things to make sure your images look good here:
either:
- save the image in 1280 size sharpened it to your taste, then save it as 90+ (very high quality) jpeg and upload.
or
- save the image as bigger than 1280 (like 3000 wide) sharpened to your taste and let the POTN uploader handle resizing. In this case the original jpeg compression level does not really matter much.
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Here is one test image I found from my disk, not my image but I think I can put it here for educational purposes. As you can see the detail is as good as it can be on 1280 size, you can read the smallest texts and there are virtually no halos or moiré.
Original size was 3600x2400
CLICK THE GLASSES ICON TO THE RIGHT TO VIEW IN 100% view.
HOSTED PHOTO
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On this one (mine, a test shot for one poster a long time ago), you can see that the sharpening won't touch the unsharp areas, as it should be. The trumpet player is in focus.
Original size was 3504x2332
CLICK THE GLASSES ICON TO THE RIGHT TO VIEW IN 100% view.
HOSTED PHOTO
please log in to view hosted photos in full size.
Hope this helps.
