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Shrinking filesizes for posting to the forum.

 
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g4lab



Joined: 23 May 2008
Posts: 1424

PostPosted: Sat May 14, 2016 11:15 am    Post subject: Shrinking filesizes for posting to the forum. Reply with quote

Could I ask the list membership to post a procedure(s) for shrinking images from the multi mb filesizes that they are , even with the smartphone, down to
the 300K and 1000x1000 size that is required to post them here?

What is the technique to do this optimally? I saw a webpage (or maybe a book page) recently that admonished the reader to "not shrink images in PS" which I believe there is no avoiding.

Procedures for PhotoShop and LightRoom would be appreciated.

Thanks in advance
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ChrisR
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Joined: 14 Mar 2009
Posts: 6994
Location: Near London, UK

PostPosted: Sat May 14, 2016 1:36 pm    Post subject: Reply with quote

For Photoshop it was/is "Save for Web" or "Save for Web and devices". The dimension part is easy (up to 1024 x 1024), and you have to set the Quality (try 7 out of 10) to get the size in bytes. It's an iterative and imprecise process.

And it can be done better:
http://www.photomacrography.net/forum/viewtopic.php?p=177843#177843
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JL



Joined: 02 Feb 2014
Posts: 120
Location: Houston, Tx

PostPosted: Sat May 14, 2016 2:56 pm    Post subject: Reply with quote

Alternatively you may try ImageJ, an open and free image processing software. When you have opened the image that you want to reduce, go into the "Image" menu tab, then into "Scale..." and select the size in pixels of the new picture.
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 17872
Location: Richland, Washington State, USA

PostPosted: Sat May 14, 2016 7:37 pm    Post subject: Re: Shrinking filesizes for posting to the forum. Reply with quote

g4lab wrote:
I saw a webpage (or maybe a book page) recently that admonished the reader to "not shrink images in PS" which I believe there is no avoiding.

At the risk of sounding opinionated about opinions, my take is that people who say "don't use popular product X" can safely be ignored unless they tell you very specifically why you shouldn't use it.

Photoshop has a number of aspects that may be important in specific cases. If you're a graphics arts professional developing web materials, then the chroma subsampling issue discussed in the earlier linked thread may be critical because there's no way to work around that one. Likewise Photoshop does not do a good job at automatically anti-aliasing textures that are vulnerable to moiré. That one can be worked around by manually filtering, as discussed at http://www.photomacrography.net/forum/viewtopic.php?t=19456 . Photoshop also exhibits the "gamma resizing error" that is discussed at http://www.4p8.com/eric.brasseur/gamma.html . If that's a problem, it can be worked around by manually converting the image to a custom RGB profile with gamma=1, doing the resizing, then converting back to sRGB for posting. If you're a purist, you might be disturbed by the fact that Photoshop only does bicubic resampling and not, say, some higher order Lanczos.

All those things noted, I usually use Photoshop because it's convenient and works very well for the images that I usually have.

Normally I do just a straightforward Image > Image Size... with basic "Bicubic" resampling (the one labeled for "smooth gradients"), then I apply a bit of USM sharpening to taste (typically 0.7 pixels at 35%), and finally do a File > "Save for Web & Devices", which Adobe has relocated as File > Export > "Save for Web (legacy)" in the latest versions. If moiré is a problem, I'll do the manual filtering and selective masking stuff as linked above. I don't recall ever using the gamma workaround for a real application.

--Rik
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barnack-bill



Joined: 29 Mar 2016
Posts: 33

PostPosted: Sun May 15, 2016 6:23 am    Post subject: Reply with quote

In Lightroom it is just a matter of exporting the image to a convenient location for uploading. I have a folder called 'forum uploads' but it is entirely discretionary.

File export format jpeg, set long edge at 1000, limit file size to 300k

This is a screen capture of the export dialogue. File can also be renamed during this process.

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