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Posted: Wed Mar 11, 2009, 18:56 (2996 days ago)
Modified: Mon Jun 22, 2009, 18:01 (2893 days ago)
(admin: this guide was written by rafinmelb -- thanks!)
The Panachallenge rules have two size requirements, a resolution requirement and a file size requirement. The combination of factors sometimes gets new users a little confused and they end up with an image with correct file size but so small on the screen that it cannot be fairly judged or alternately with an image the correct size on the screen but that is over the size limit.
There are a number of tools that allow you to resize images. Below is an example for Adobe Lightroom.
The screenshot below is from Adobe Lightroom 1.2. Lightroom controls both pixel size and jpeg quality (hence file size) in the one single dialogue making things a little simpler.
You will notice in the dialogue below that I am using a preset called “panachallenge”. This has allowed me to save my basic setting so that I do not have to start from scratch each time. To get to this dialogue I use the File/Export menu.
I select the panachallenge preset which gives me this dialogue. The first time through you might choose a series of settings that work for you and in the Preset field choose the Save Current Settings as Preset option. This will allow you to save an export preset as I have done above
You will notice that I have set up a destination folder specifically for files exported for Panachallenge. This helps me keep track of them.
The important points though are the Quality slider and the Constrain Maximum Size” set of fields.
Generally I start with the Constrain maximum size. My default setting above constrains both sides to a maximum of 800 pixels. This is great for 4x3 images produced by Panasonic cameras. This will make the longest side 800 and by default make the shortest side 600. I normally recommend that you select the longest size:
* 800 for a 4x3 ratio (it will give a width of 600)
* 900 for a 3x2 ratio (it will give a width of 600)
* 1024 for a 16:9 ratio (it will give a width of 512)
Of course you can choose other sizes and ratios but make sure that the sum of the two pixel values is not more than 1600.
I then use the slider to adjust quality. My default is 78 and this seems to work reasonably well. However If after I actually export I see that the file is too large I have to come back and choose a lower quality. Alternately if the file is reasonably small I choose a higher quality.
I might need to go through a couple of cycles of this, resaving the file and adjusting the quality level till I get a file the fits into the overall 250K limit.
Once I have done this I review the resultant file. I might decide that the compression level has sacrificed too much quality. I might then decide to choose a smaller pixel size and would therefore go back to the Image/Image Size menu again. Of course I would revert to my unresized original before a second resize cycle.
Generally the more fine detail in an image the larger it ends up being and therefore the more we have to compromise quality to fit the size criteria. Alternately you can increase quality but decrease size.
A link to some adobe self help references: http://livedocs.adobe.com/en_US/Lightroom/1.0/WS75C39DDC-B701-4840-A703-0755A5C04878.html