Resizing Photos vs. Image Quality

Discussion in 'Casual Photo Conversations' started by patrick.mason, Apr 28, 2008.

  1. How does one resize a photo from, in my case, 13.5 MB to a mere 3 MB and not have it look like crap?
    Sorry, I'm a bit frustrated about this. I know how to capture and process my work, I just don't see the efficacy of compressing a beautiful picture down to a representation that looks nothing like the original.
    My passion is landscape photography. I have great equipment and software... I'm just at a loss as to how
    others are getting around this. Educate me, please!

  2. There are constant debates about this sort of thing, but changing the image to between 180 to 360 to 600 dots per inch at any given size will normally produce an more (at the upper end) or less (at the lower end) acceptable print for viewing. Much above 360-600 dpi is 'wasted' in that a 1000 dpi print will not necessarily look much better to the eye than a 600dpi. In any case, all reduction in the _quantity_ of data will necessarily lead to some loss in _quality_, so the issue is one of how much of a 'hit' in data loss can you take before the result is unacceptable to the viewer (and to you). This is what our friends in the Warsaw Pact countries used to call a "contradiction" and in this case it is not resolvable. It's for you to decide how much 'crap' you will tolerate.
  3. Patrick: when you say "resize" are you talking about:

    1) the size of the image file (in Mb) for a particular image dimensions (in pixels),

    2) reducing the dimensions (in pixels) below the optimum for some particular printing process,

    3) changing the dimensions (in pixels) for the best look on a particular display/printing process, or

    4) applying adjustments (ex. sharpening) specifically "tuned" for some particular output process and image dimensions?
  4. Are you asking about resizing and compressing for monitor display for the web or other onscreen use? Or for print?
  5. Just reread my post above. I apologize for not clearly stating that my frustration is about
    the constraints of this site, Is everyone limited to 3 MB pictures? They sure
    don't look like it to me... that is until I scrunch my photos down small enough to comply
    with the maximum size of 3 MB. I understand the necessity of having some maximum
    limit, but GeeezLoueeez!

    By the way, the method I use to 'downsize' my photos in PS is using the 'transform'
    function to size the photo, then crop it. The JPG doesn't look half bad, but by the time I
    post it there's no resemblance.
  6. I'm not sure what the advantage would be to uploading a 3 MB photo to the web. Even with DSL I wouldn't wait for one to load.

    Granted, an 800x600 JPEG may not reveal the subtleties in the breadth and scope of a landscape, but that's the nature of the web. Just as I wouldn't use a 12"x12" frame to examine a Monet bit by bit at the museum, I wouldn't want to scroll left and right, up and down to view an oversized JPEG online.

    You may be underestimating the ability of viewers to appreciate your photos, even in an 800x600, 250 kb file.
  7. You may be very correct Lex, I hadn't given that much thought. OK. Then how do I guarantee my photo is a) Under 3 MB AND no bigger than 1500X1500 pixels? I just tried
    submitting a 2.7 MB photo and was refused because of its dimensions. How do I know
    what the new dimensions are in PS? As a matter of fact, I don't know how big the JPG is
    until I actually save it! I've just got to be missing something really simple here... and, I'm
    not smarter than a 5th grader! :cool:

    Thanks so very much for the responses...
  8. I haven't used Photoshop in years (last time was on an old Mac). But most photo editing software allows you to specify the dimensions after resizing/resampling.

    Also, some software will even let you examine the effects of JPEG compression before committing to the final version. My old copies of Corel Photopaint 8 and Jasc Paint Shop Pro 7 offer this preview feature.

    Otherwise, I use 85%-95% quality for saves to my portfolio, and only 60%-75% for saves to 500 pixel wide photos for display inline with discussion threads.

    Generally - and there's no rule here - I don't see a lot of difference between, say, a 600x400 photo saved to a 100 kb file size and 200 kb file size. In some cases, compression can affect the appearance of large expanses of same or similar colors such as blue skies, so a bit less compression may be needed. Likewise, I don't see a lot of difference between a carefully prepared 800x600 JPEG that's 150-250 kb in file size and one that's 500 kb or larger.

    If the quality was in the original, it usually won't be lost with a reasonably well prepared JPEG.

    Another key - avoid oversharpening. It'll show up as halos and artifacts in your portfolio.
  9. Lex your remarks... very timely. Thank you. I agree about sharpening. I only sharpen to
    compensate for the filter in front of the sensor, I let the 1DS do the 'heavy lifting'. I figure
    if it isn't sharp enough after that, I screwed it up. Regarding my software: I may have to
    find someone who has the same setup I have... PhotoShop Elements 4.01.0 + new iMac.
    Maybe the finer points of knowing all the parameters just weren't included in the 'strip-
    down' version of PS... ? I love the editor and tools it just seems like I'm flying blind in this
    area of photo downsizing, etc. At any rate... THANK YOU, you're a gentleman and a
    patient one at that!

    Patrick, JUNEAU ALASKA
  10. "Then how do I guarantee my photo is a) Under 3 MB AND no bigger than 1500X1500 pixels?"

    I don't have Photoshop handy, but this is the general approach:

    1. Resize (dimensionally) from your source image to 1500 pixels in the longest dimension. Image->Resize I think. Make sure to check the "resize" check box. Choose bi-cubic normally, or just resample if you want to maintain the appearance of whatever grain and noise that may be in the original.

    2. File -> Save for Web. Adjust the quality slider and look at the output file size; repeat until done. Image quality generally won't suffer (past cursory inspection) until compressing past about 10:1 for jpeg.

    By the way, you'll find sharpening generally unnecessary when down sampling to reasonable web posting dimensions. 1500 pixels on a side is really way overkill for that matter...
  11. Thanks Robert, I'll checkout my drop-down menus a bit more closely. I get so used to the
    post process work flow, I don't even see the other menus. Many thanks again, to all!

  12. Hello Patrick. Leaving the indepth technical discussion to others (for once), here is one quick and dirty Procedure for "downsizing" a large hi-res digital picture file to any size you want or need. You can do this procedure on *any* Windows pc or laptop, and you dont need any other software. This is the procedure i use to greatly downsize Large_Fine_Jpegs (from my D300) for upload to Photo.Net threads.

    1. Locate the omnipresent Windows Paint program. Its under START => PROGRAMS => ACCESSORIES => PAINT. Launch that program.

    2. Load up your hi-res full color JPEG. (Yes, if you shot in RAW, you'll need to convert to hi-res JPEG).

    3. In Paint, at the top, look under IMAGE. The two functions needed to resize the picture file are ATTRIBUTES, and STRETCH/SKEW. With your picture file loaded, click the ATTRIBUTES function. A box will pop up, showing you various image attributes,includeing the pixel dimensions along both axis. That's your starting point.

    4. Decide how much you want to resize the image (up or down). For example, for uploads to PN, the moderators say the LONGEST axis should only be about 520 pixels wide. That means you have to downsize the image dimensions to meet that spec.

    5.Now click the STRETCH/SKEW function. There are 2 fields where you plug in the resize % factor for both X & Y axis. I usually just plug in 50 in both fields. That makes Paint resize my image downwards by (-) 50%.

    6. Now check the ATTRIBUTES again, to see how the Pixel Dimensions look now. See how close or far away the Pixel Dimensions are from your desired dimesnions.

    7. If necessary, repeat the STRETCH/SKEW step 2 or 3 more times by using your best guess for the desired % Resize factor. After doing the Stretch/Skew step, check the ATTRIBUTES again, to see how the Pixel dimensions are looking.

    8. As you get close to your desired Pixel Dimensions, you start fine-tuning the % Resize Factor. Instead of 50% factor, use a 99% or 97% factor. This will resize the image downwards just a tiny bit, until you finally reach the dimensions you need.

    9. When the image is finally at the dimensions you want, then just do a SAVE AS on the file, and save the file back out to the local PC hard drive. You do not have to alter anything else on the image.

    10. When the file is saved, then exit out of Paint, and do a right-click on the new (resized) image file, and select Properties, to see what the new filesize is.

    This is a very easy way to quickly and painlessly downsize any image file that Paint can load.

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