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Large scale image size reduction help

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  #1  
Old 09-15-2009, 10:32 AM
julius julius is offline
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Large scale image size reduction help

Hey guys!

I have really large images 12,000px x 12,000px. Now, they look fantastic but when i scale down these images down to 450px, i lose lots of quality.

Right now i'm just using the photoshop scale tool and optimizing for reduction.

Any tips as to what i should do to maintain quality?

Thanks for the help!
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  #2  
Old 09-15-2009, 11:07 AM
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Der_W Der_W is offline
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Re: Large scale image size reduction help

Scaling images down will always result in loss of quality. You can try to sharpen the images after scaling (down sampling reduces loss of sharpness because of the interpolation) by using the "Filter"-"Sharpen"-"Unsharp Mask" or the "Filter"-"Sharpen"-"Smart Sharpen", but don't expect the images to come out perfect.
Btw., you should always try to name your problems because in most cases this will as well help you to remove/avoid/or at least reduce these problems.
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Old 09-15-2009, 03:13 PM
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mistermonday mistermonday is offline
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Re: Large scale image size reduction help

Wow, 450 pixels is pretty small - that's abpout 1.5 inches at print quality. I assume you are making a thumbnait for web viewing or something like that. If that's the case, you may do better to fit the whole image on your monitor, take a screen shot, paste it into a new PS document and downsize it from there. You could also create an action in PS to scale the image down many times by a smaller amount.
Regards, Murray
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Old 09-15-2009, 03:37 PM
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garibaldi garibaldi is offline
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Re: Large scale image size reduction help

Try image size, input yoru dimensions hit ok. then go to sharpen, fade sharpen by about 50 or so, and then use save for web and that will let you tweak and optimize the image
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Old 09-15-2009, 07:57 PM
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TommyO TommyO is offline
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Re: Large scale image size reduction help

Julius,
Always adjust your pixel depth (resolution) first. For instance, in the Image Size dialog, first change your pixel (depth resolution) to 110 ppi or 72 ppi, whichever you prefer. Check the Resample box, then pick the Bicubic Sharper resampling method. Allow it to do its work. Then go back and do another Image Size, this time only changing the Width to your preferred size, i.e. 450 pixels, with all the same options checked/selected. You'll find the final reduction much more acceptable.

Here is an example from a 24MP image, using the same reduction ratios (1:27). The first is the original; the second was via dimensions first (as you did); the third was two steps with pixel depth first (as described). The posted images may be different internally, but visually represent the differences in the processes correctly (the idea was to get the picture across). But, you can see there's a big difference in visible quality for a small print/image.
Attached Images
File Type: jpg Bird_before.jpg (198.6 KB, 13 views)
File Type: jpg Bird_dimensionfirst.jpg (78.6 KB, 10 views)
File Type: jpg Bird_pixeldepthfirst.jpg (186.6 KB, 12 views)
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Old 09-15-2009, 08:08 PM
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Re: Large scale image size reduction help

Thanks everyone for the downsizing tips.
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  #7  
Old 09-17-2009, 10:03 PM
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garibaldi garibaldi is offline
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Re: Large scale image size reduction help

If all else fails, just leave it the big size it is and keep walking farther and farther away unitl it looks about the size you want
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Old 09-17-2009, 10:40 PM
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seattle-light seattle-light is offline
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Re: Large scale image size reduction help

You're going to lose a lot of detail and quality no matter what you do, because you're reducing you're resolution by a factor of more than 26. You might want to consider doing an intermediate scaling from 12,000 to 1,800 and then do a fairly radical oversharpening (say Unsharp Mask at 100, 6 pixels, 10 threshhold to start) and then scaling it down to 450 (which is then a clean 4 to 1 downsampling so there's not a lot of new pixels being created interpolation -- each 4x4 square of pixels in the intermediate step is yielding 1 pixel -- this is what I call a clean bump, and it can make a dramatic difference in the resulting quality). You'll have to try different settings to see what works best for your images. If you scale the big image down to the final size and then try to sharpen it, you will already have squished a lot of the data. Any sharpening done at final sizes should be done with care. Good luck. Sharper images require higher quality settings when being saved as JPEGs (or the improvement of sharpening will be lost in chunky JPEG artifacts) and they make bigger files at the same settings (because there are more distinct differences for the compression algorithm to describe). So there may be some compromises along the way. Good luck with that. Alan.
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