Thanks useful information: 
How to resize your photographs for posting on the internet.
Many photography forums have size limits that apply to both the physical and file size limits that apply when you post your photographs to the sites.
There are two sorts of image size to consider, please keep this in mind when reading this tutorial:
- The number of pixels (width and height)
- The file size, set by JPEG compression levels
There are many ways to resize photographs for display on the internet, and an even larger range of photo editing software to do the resizing in. This tutorial is for Adobe Photoshop. Most other software packages offer similar menu options, so it may mean using the help feature in your software to convert these instructions to your own software.
Ausphotography has the following limits
* 1024 pixels maximum on the longest side and 250kb file size
Except
* The panoramic forum, which has a limit of 1200 pixels and 350kb file size -see here for info
* Photos linked from external sites do not have size or a KB limit, they are resized on the fly (but keep the file-size down as a courtesy to other members bandwidth)
Resizing your Photograph
Open your Image in photoshop and do all your post processing.
When completed and ready to resize, Go to the menu and select Image > Image size
If needed change the ‘dimension’ to pixels. Make sure ‘constrain proportions’ is ticked and also ‘resample image’. Leave the resample method at the default – you can experiment with that later if you like, but its outside the reason for this tutorial.
Looking at the pixel dimension area of that screen, find which is larger of width or height, click in that box and type 800 (or whatever size you want/need). As below:
The Resolution box will determine the quality of your resized photograph. I leave mine at 240 normally, you can go lower, but if you go under 100 you risk seeing a visible deterioration on the quality of the final resized photograph.
Click OK. Photoshop will now resize your image automatically.You are now ready to save your photograph at the new size for uploading to the internet
In Photoshop there are two ways to save the resized photograph. Both are detailed below.
Using the “File > Save As” method
This method retains all your EXIF data, so is worthwhile using if you want other members to be able to view important data about your photograph, including, Camera used, shutter speed, aperture and ISO (and a lot more).
Firstly to save using this method your photograph must be in 8 Bit, go Image > Mode > check that 8 bits/channel is selected (if not - select it now).
Then go File > Save As
There are a few things to do on this screen. mainly, select where you are going to save this version of your photograph on your hard drive, give your file a name in the File Name box, and select JPG in the Format Box (if JPG is not available, you haven't changed your image to 8 Bit - see above). Once done, click Ok
You will then get a quality screen pop-up.
You will need to adjust the slider until the file size is below the required for the website where you are placing your photograph. As you adjust the slider, the file size data (to the right of the slider will change automatically). When done, click OK.
You have now saved your photograph at the smaller size (800 pixels in this example) and at a KB filesize appropriate for uploading.
Using the “Save for web” method
This method strips your EXIF data and therefore will not allow other members to see technical information recorded about the photograph.
Once your image is resized (as per the resizing instructions above)
Go File > Save for Web and Devices
On this screen there are several things to do as well, In the group of sliders on the top right, you will need to adjust the quality one to increase/decease the KB size to suit where you are uploading your photograph to. Under the bottom left corner of the photograph is a small text showing the KB file size, so adjust the quality slider until the KB size is appropriate.
Also in the sliders area is the "preset" option, to the right of that is a small triangle, click that triangle and select 'convert to sRGB'. The internet is optimised to work in the sRGB colourspace, so you might as well have your photograph in the same colourspace.
When you have got your photograph in the right KB file size, you are ready to save it, Click Save (top right). You will then be presented with a screen to select where on your hard disk you wish to save your photograph and the option to name it as well.
When you have set these, Click Save.
I hope this tutorial is useful to you and even if your do not use Photoshop to edit your photographs, that you can convert these instructions for your own software.
Please feel free to discuss this tutorial, if you pick up any errors in the above, let me know. If you use a different software package and wish to add your own tutorial, you are most welcome to.
If you do not have Photoshop and use Windows XP, you can try the free Image Resizer offered by Microsoft here, down the right hand side of that page find the Image Resizer file and download it. Then when you right click a photo using explorer you can quickly and easily resize it.
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Addendum:
There are two main controls for image file size when saving as a JPEG image.
First is the size in Pixels.
I.e. The number of pixels width x height.
Changing the size in Pixels has a secondary effect of changing the file size.
Eg. an image 3000px x 2000px resized to 1000px x 667px will be a smaller file, 6,000,000px
down to 667,000px.
But is the file small enough?
Secondly, the JPEG compression setting.
File size can also be adjusted by setting the JPEG quality (1-100) when you save the image.
The quality is also another way of saying which compression level you want.
The more compressed the image the more detail you may lose.
So to size an image for AP you should set the pixel size you want (typically no more than 1024 on the longest edge)
and adjust the JPEG quality (compression) to get the file size under the 250kB limit.
Some other advanced controls that have a minor effect on the image size are:
- Including meta data all, in part or none
- Saving baseline or progressive (and how many scans, 3 or 5 etc)
- Saving colour profile information (don't bother with sRGB as that's the web default)
Note: You should always make sure the image is saved as an sRGB colour profile for web publishing.
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