Board index Photography Technical Questions Quality of photos after size reduction

Technical Questions

Quality of photos after size reduction

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trut_maluglist
 
Posts: 52

Quality of photos after size reduction

Post Fri Aug 01, 2008 9:24 am


I'm new to PBase and notice that the quality of my 5.6 MP photos in one gallery in which the photos are sized down to 900x600 is not as good as the quality of my 5.6 MP photos in another gallery in which the photos are sized down to 800x537. The 900x600 photos appear pixelated, yet looking at the file size, are almost twice the size (~220 kb) as the 800x537 photos (~120 kb).

Could it be that I downsized the 900x600 photos using Irfanview and downsized the 800x537 photos using WebGems? I plan on running a test by downsizing a sample from each slideshow to the other size and also using the other batch resizing application. This should give me some answers. But it still puzzles me that a 5.6 MP photo downsized to 900x600 ends up as lower quality than a 5.6 MP photo downsized to 800x537, when the 900x600 image ends up nearly twice the file size as the 800x537 image.

dougj
 
Posts: 2276

Re: Quality of photos after size reduction

Post Fri Aug 01, 2008 10:19 am


I suggest you post the links to some example photos, maybe some folks can help.

trut_maluglist
 
Posts: 52

Re: Quality of photos after size reduction

Post Fri Aug 01, 2008 10:30 am


dougj wrote:I suggest you post the links to some example photos, maybe some folks can help.

Good idea!

http://www.pbase.com/trut_maluglist/image/101017779
This photo was downsized using Irfanview to 900x600 and is about 220 kb




http://www.pbase.com/trut_maluglist/image/100578574
This one was downsized using WebGems to 800x537 and is about 140 kb

This is kind of strange. In this post, I put tags around each URL and only the word 'Image' appears. So I guess I can't actually post the photos here, but I can post the hyperlinks.

trut_maluglist
 
Posts: 52

Re: Quality of photos after size reduction

Post Fri Aug 01, 2008 11:31 am


I've made a test gallery. http://www.pbase.com/trut_maluglist/test_gallery

two are downsized using ACDsee (default jpeg quality)
two are downsized using WebGems (jpeg quality 85%)
two are downsized using iview (whatever the default jpeg quality is & no sharpening)
one is imported from my other PBase gallery

The Irfanview photos don't look anywhere as good as the ACDsee or WebGems photos. I'm using the default settings in Irfanview. 'Sharpen' isn't even checked. I guess I could use WebGems to downsize, but I'm puzzled why the Irfanview downsized images aren't as good.

dougj
 
Posts: 2276

Re: Quality of photos after size reduction

Post Mon Aug 04, 2008 12:11 am


It looks like you're well on your way to sorting this out, I'll add just a few comments & observations. ACDsee and Webgems are doing a much better job in avoiding jaggies and other compression artifacts. I don't use either of these programs, I have Irfanview but I don't routinely use it for resizing. I did try an experiment with a 30D file with Irfanview, and produced both acceptable and poor resized files. When resize/resample is used the resulting 800 wide pixel image is fine, using the resize option only (no resample) the image shows a lot of compression artifacts. It's a question of trial and error with the programs to determine the optimal settings.

Prior to uploading a photo to PBase, you can open it in your browser and see what it will look like when viewed in its original size on PBase. The original sizes are displayed as received, viewing the other sizes reveals the effectiveness of PBase's resizing. Good luck!


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