Why can't I get rid of my jpeg artifacts?

Discussion in 'Digital Darkroom' started by greg_adkins|4, Jan 23, 2003.

  1. I'm having trouble with jpeg artifacts in this image I've uploaded to PN. I scanned this at 600dpi using an Epson Perfection 2450 Photo scanner. I used "Save for Web" in PhotoShop 6 to resize the image to 600x600 and save in jpeg format. I've tried many different levels of compression and I've even tried scanning at 300 and 800 dpi, but I can't seem to get rid of the artifacts. Interestingly enough, I have successfully uploaded this image (although it has a border and is slightly smaller) to my website.
    What can I do to clean up the artifacts in this image? Should I be using a 3rd party jpeg compression tool like Jpeg Explorer instead of PS? I'm trying to keep the size under 100k as specified by the PN guidelines. Is this absolutely neccessary? I'm sure PN will compress my image if I don't, but if that's the only way I can get a clean image...how can I tell?
    I've searched the archives, and there's so much on jpeg compression, etc., but I can't seem to locate an answer. Please help!
  2. Jeremy Stein

    Jeremy Stein Moderator

    I looked at this picture, and, for one thing, it is only 400x398 in large view on photo.net, and it is only a 24k file in photo.net. Are you sure that you resized it to 600x600 and nearly 100k jpg file? Second, I don't see any jpg artifacts, although I see jaggies clearly, but I think the jaggies are due mostly to the small size of the pic. The other image link did not work for me, so I have nothing to compare the first pic to.
  3. Oops! This image was resized to 400 pixels in height, not 600. My mistake. I'm not sure why the second link didn't work for you, Jeremy. Why would the small size contribute to the jaggies? I've tried image sizes from approximately 70kb to 100kb as well and they still appear.
  4. This is a tough image for JPG in that the border between subject and background is a sharp edged change in color as well as brightness. I can't see artifacts in the posted image but I bet that border is where you're having problems.
  5. When you have fine detail and crisp edges, you simply haev to use a higher quality setting to get a decent image. I would say a quality of 60 to 80 in PS, but I'm not positive what I saw was JPEG artifacts. It looked more like you downsampled without bicubic interpolation set, which can basically throw out pixels and cause jaggies.
  6. One of the reasons I removed most of my images from this site was because photo.net was re-compressing my already compressed jpeg and they looked like crap.
  7. to ilustrate my point I just uploaded this image to photo.net. The size was 62kb. after upload the size was 23k. On the left/top is the image from my website 62k, on the right/bottom the one from photo.net. While the casual snashooter might not be able to tell the difference, in my opinion the image is ruined (see artefacts and loss of shapnness near the petal edges, etc)


    I think this is an awful thing to do on a photography site. If they have hardware/space problems they should consider limiting the number of images people upload not screw up their images. But it's their right to set their own policy, I just chose not to use the site for posting images.

  8. After reading the above responses, it seems as though what I'm terming "artifact" is actually "jagging". This is appearing along the border defined by the sky and the two objects, as well as on some of the sharp lines on the objects themselves.

    I've only resized my image as described. I haven't used any downsampling techniques, and I've tried maximum quality (lowest compression) in saving my jpegs, but to no avail. The reason this is puzzling me is because I don't see this on the images I've viewed on PN. One thing I have noticed is that when I zoom in PS, sometimes the image can appear jaggy, depending on the zoom factor. Does this sound familiar to anyone?

    I know this could be a common occurrance, but what could be causing this using the techniques I've described? Is there an effective way of eliminating this?

    Thanks for your replies.
  9. Sorin's posts make a valid point, and it appears that PN does re-compress images (as stated in the image submission guidelines), but I've verified that the "jagging" exists by viewing my jpeg before I upload my image to PN. I'm just trying to prevent this from happening on my end before I upload new images.
  10. One of the (several) reasons why I don't have a portfolio on PN is that they muck with the image when gets uploaded!! I think that's an unspeakable and bizarre thing for a photography website to do!
    If PN has disk space issues then they should simply limit uploads for each user to some maximum. No one needs to have 30 or 40 images up here, or if they do then THEY (the photographer) can compress them. If everyone had, say, a 500K limit they could have 5 100K JPEGs, which is pretty good resolution, or 10 50K JPEGs which isn't bad for the web, etc. If someone needs to put up more images they can get their own website, like I did.
  11. Just to keep things on track, let me just state that this is not about what happens to my images after they are uploaded to PN. I want to know what I can do to prevent the jagging before I upload them to my folder.
  12. Greg, the process of reducing the image size is down-sampling. I use the "Image Size" dialog to do this and you can choose the algorithm there. I don't know if you can change it in the "Save for Web" dialog.

    One reason I don't do that there is that I always sharpen the image after downsampling. Then I use "Save for Web" to set the compression level. Again this does not look like JPEG artifacts.
  13. Thanks for pointing that out, Jim. Now, your first response makes a lot more sense to me. Ha!

    One thing I've just noticed is that the "jagging" appears only when I view the image on PN! The responses have helped me delineate the difference between "jagging" and "artifact" and I can now confirm that this is not artifact. In my original post I was referring to the "jagging" and if I right-click on the "large" image and select "save image as", I don't see the jagging! This really confuses me, but I guess it must have something to do with the way PN handled my uploaded image. It doesn't show "artifact" like Sorin's excellent example, but it shows the "jagging" or a sort of "anti-aliasing" on steroids.

    Ok, I've definitely learned a lot here, and if anyone can lend any additional insight as to what's happening here, that's a bonus!

    Thanks to everyone for their thoughtful responses!
  14. I'm with Peter on this one!!! Taking any submitted images and recompressing a second time is a big NO-NO!!!! I checked my images, which were all close to 100K, and was surprised at how MUCH they had been recompressed - all so Joe Sixpack can upload 500 images of his family album. I was wondering why they never looked as good. I will submit no more untill the policy changes. It is a policy that does not promote good photography.
  15. I'm with Steve and a while ago, I deleted all of my photos for the same reason. Of course, since I'm a non-paying "freeloader," I don't feel I have much right to complain about photo.net's policies and practices...

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