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Resizing Photos vs. Image Quality

Patrick Mason , Apr 28, 2008; 05:54 p.m.

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!

Patrick, JUNEAU, AK

Responses


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JDM von Weinberg , Apr 28, 2008; 06:07 p.m.

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.

Geoff Sobering , Apr 28, 2008; 06:22 p.m.

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?

Lex Jenkins , Apr 28, 2008; 06:23 p.m.

Are you asking about resizing and compressing for monitor display for the web or other onscreen use? Or for print?

Patrick Mason , Apr 28, 2008; 08:06 p.m.

Just reread my post above. I apologize for not clearly stating that my frustration is about the constraints of this site, Photo.net. 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.

Lex Jenkins , Apr 28, 2008; 08:11 p.m.

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.

Patrick Mason , Apr 28, 2008; 08:36 p.m.

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! 8-)

Thanks so very much for the responses... Patrick

Lex Jenkins , Apr 28, 2008; 08:45 p.m.

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 photo.net portfolio.

Patrick Mason , Apr 28, 2008; 09:11 p.m.

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

Robert Lee , Apr 28, 2008; 11:11 p.m.

"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...


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