reducing image size for web pages?

Discussion in 'Digital Photography' started by Paul Heslop, Jul 7, 2005.

  1. Paul Heslop

    Paul Heslop Guest

    what's the best way to reduce image size but retain sharpness? I
    sometimes sharpen a little before reducing and that can help but other
    times not. Any suggestions?

    pref size of reduced image to be

    640 x 480
    Paul Heslop, Jul 7, 2005
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  2. Paul Heslop

    Ed Ruf Guest

    First, how are you resizing them? Simple resizing, or resampling using what
    method? Second, apply sharpening after not before. Sharpening is always the
    last operation performed.
    Ed Ruf, Jul 7, 2005
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  3. Paul Heslop

    DCD Guest

    Always resize first, then sharpen last. Sharpening before resizing
    probably won't help much. It depends a bit on which resampling scheme
    you use. Bicubic will retain more sharpness than weighted average
    resampling, but I think the results of weighted average + unsharp mask
    look better.
    DCD, Jul 7, 2005
  4. Paul Heslop

    Alfred Molon Guest

    Try the Lanczos filter for resizing, then apply some unsharp mask with
    radius 0.3 and amount 40-70. It's the resizing method I applied here:
    Alfred Molon, Jul 7, 2005
  5. Paul Heslop

    Paul Heslop Guest

    just straight resizing, Ed... I only recently read a little article
    about resampling but it all kind of went over my head
    Paul Heslop, Jul 7, 2005
  6. Paul Heslop

    Paul Heslop Guest

    Up to now I have just been allowing the program, paintshop or
    whatever, to resize for me... but I have seen people's resized pics
    which look a hell of a lot sharper than most of mine ever have.

    How do you resize in this bicubic way?
    Paul Heslop, Jul 7, 2005
  7. Paul Heslop

    Paul Heslop Guest

    wow, I am very impressed! Where does the lanczos filter come from? Is
    it part of a program or do I need to hunt it down?
    Paul Heslop, Jul 7, 2005
  8. Paul Heslop

    Paul Heslop Guest

    Oops, never mind, found it! :O) Looks better, for sure
    Paul Heslop, Jul 7, 2005
  9. Paul Heslop

    DCD Guest

    Bicubic is a Paint Shop Pro option, but most image editors have a
    variety of resampling techniques available. For example ther might be
    Nearest Neighbor, Bilinear, Bicubic, Lanczos, Mitchell, and Catmull-Rom
    options. The best ones are the slowest, and while when upsizing you
    probably want to use the best (and slowest) choice, for downsizing you
    can sometimes get better results using an averaging option and then
    resharpening. This can reduce the visisbility artifacts and grain in
    the original since they get "averaged out" in the downsizing process.
    Different images may look better when resampled with different
    techniques. There isn't really one which is always the best for every
    DCD, Jul 7, 2005
  10. Paul Heslop

    Ed Ruf Guest

    For default if you have PSP7 or later I'd set SmartSize for the resample
    method. Then after resampling apply a bit of Unsharp Mask beginning with:
    Raduis = 1.05
    Strength = 75 - 85
    Clipping = 8
    as a start.
    Ed Ruf, Jul 8, 2005
  11. Paul Heslop

    Stacey Guest

    What software are you using? Makes a difference on what is best..
    Stacey, Jul 8, 2005
  12. Paul Heslop

    Don Wiss Guest

    Hi Paul,

    This is something I recently posted as part of another article:

    Picture Reduction Scheme
    I posted an article in asking for suggestions on how I
    should reduce these pictures while maintaining quality. (They were taken in
    1600x1200 resolution with normal compression.) No one responded. So I spent
    a lot of time thinking about it. I noticed that when using jpegcrop that it
    only offered reductions in 1/8s. Or 12.5%, 25%, 37.5%, 50%, 62.5%, etc.
    Knowing that lossless cropping meant the dimensions were still divisible by
    eight, I knew that if I kept to reductions in eights I would not have
    fractions of pixels. Previously my pictures were taken in VGA resolution,
    or 640x480. So pictures in my albums were that size or smaller (if
    cropped). I decided to use an algorithm based solely on height. With wide
    ones scrolling sideways, as if they were a stitched panorama. So I first
    determined whether the picture was in portrait or landscape orientation by
    comparing its height and width. Then I used this algorithm:

    Portrait Landscape
    <= 640 100% <= 480 100%
    <= 728 87.5% <= 544 87.5%
    <= 848 75% <= 640 75%
    <= 1008 62.5% <= 768 62.5%
    <= 1280 50% <= 960 50%
    <= 1600 37.5% <= 1200 37.5%

    For the reduction I used Easy Thumbnails, calling it using the command line
    prompt option under my album building program's control. I ended up with
    pictures the same height as my existing albums.

    If there was no reduction a reduced size image was not created (to save on
    host server space). If both a reduced size image exists and the original
    size, when you hover your cursor over the picture the tip will include
    [Click for larger picture].

    Don <> (e-mail link at home page bottom).
    Don Wiss, Jul 8, 2005
  13. Paul Heslop

    Destin_FL Guest

    Here's the thing about downsizing photos: If you have an image that's say 1600
    pixels wide or larger (or whatever), and you resize to 640 (or whatever) in one
    step, it ruins the photo. And yet it is what 95% of everybody does to downsize.
    Throwing away pixels in one big leap never works very well. And its why 95% of
    folks web images look terrible.
    So..... for instance in Paint Shop Pro (or whatever) start by resizing as a
    percentage, NOT as pixels. Choose something like 85%. Click OK. Now just do
    Control-Y (redo) over and over until you end up at the last possible pixel size
    OVER 640 (or whatever, but 640 in your case.) In fact you can just hold down
    the Control key and hit Y over and over.

    At that point, go back to Resize, and now choose to resize by specific pixel
    measurements. Type in your final size. 640 x 480. Click OK. Now, finally, if
    you need to sharpen, use unsharp mask a tiny bit.
    You'll find that downsizing in small steps and then to specific pixels on the
    last step leaves small photos that are almost unchanged from the original.
    Photoshop won't do a simple Control-Y for redo, so like 80% of Photoshop tasks,
    what should be a simple task becomes a convoluted, unintuitive pain. But I

    Give this method a whirl; I think you'll be amazed at how much nicer the photos
    will downsize.



    what's the best way to reduce image size but retain sharpness? I
    sometimes sharpen a little before reducing and that can help but other
    times not. Any suggestions?

    pref size of reduced image to be

    640 x 480
    Destin_FL, Jul 8, 2005
  14. Paul Heslop

    Steve m... Guest

    I use it seems to do the job and I can use it automatically
    resize any number of photos. It seems to keep the sharpness pretty well,
    The only disadvantage with it is that I must make 2 passes to get the
    pictures and other stuff setup correctly. I use the thumbnail sizes to
    resize the pictures first to 640X480 and then run it again to make the
    thumbnails of 77 x 97.
    You can see the examples of this at

    Steve m..., Jul 8, 2005
  15. Paul Heslop

    Paul Heslop Guest

    thanks for the thorough info!
    Paul Heslop, Jul 8, 2005
  16. Paul Heslop

    Paul Heslop Guest

    thanks Ed, I'll give this a try
    Paul Heslop, Jul 8, 2005
  17. Paul Heslop

    Paul Heslop Guest

    I'm hovering between Paintshop Pro 8, photoshop CS and photoshop
    elements. I have no idea why I have both of those except I hate to
    uninstall stuff unless I know it's useless.

    I prefer Paintshop because I'm more used to it.
    Paul Heslop, Jul 8, 2005
  18. Paul Heslop

    Paul Heslop Guest

    Thanks Don, I think i actually have easy thumbnails installed too so
    it's worth a try. So many options so few brain cells to be used :O))
    Paul Heslop, Jul 8, 2005
  19. Paul Heslop

    Paul Heslop Guest

    woow... intense stuff... this is going to take a lot of
    experimentation! Thanks Tim.
    Paul Heslop, Jul 8, 2005
  20. Paul Heslop

    Paul Heslop Guest

    Thanks Steve, that's one I'd never heard of before!
    Paul Heslop, Jul 8, 2005
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