[Alisdair]

If you are a Photoshop user, you may find the attached note "Photoshop.doc" useful. It explains how I use my version of Photoshop (in CS3) to set my photo sizes for our Forum. It looks quite complicated, but in practice is very quick and easy. And as it uses the Crop tool it lets you change what's in the picture at the same time - it's worth remembering that as the file size limits we have on the forum are probably much lower than the file size of your original images, you can often pick out quite small details from your original pictures to give perfectly good pictures on the Forum.
The details may be different in other versions of Photoshop, but if you follow the general principles you should be able to work out how to adapt the method. And perhaps users of other Photoshop versions will be kind enough to post their own methods/instructions for setting file sizes to our limits, using the Crop tool?

[JTh]

I ‘m using CS4, but I don’t think it differs much from the other recent versions from CS2 and up. I do it in a slightly different way from Alisdair’s description.
The photo is first cropped using either the cropping tool or the rectangular Marquee tool (when making a free rectangular shape, I click on’ Image’ after I have made the selection and then ’Crop’).
 I prefer to save it using 'Save for Web and Devices’, but usually my images are too big to be able to do that directly, so I first have to make the proper image size: I click on ’Image’, then choose ‘Image size’, at the top of the pop-up menu you set either width or height, making sure that none of them exceed the size given in the instructions for this site, width maximum of 760 pixels and height no more than 560. At the bottom of the same menu the three last boxes should be ticked and under ‘Resample Image’, I choose Bicubic Sharper (best for reduction). 
I then save the photo using ‘Save for Web and Devices’ (from the ‘File’ menu). In the menu to the right of the photo you chose JPEG format, and by clicking on ‘Quality’, you can either change the percentage or slide the ruler below until the file has the right size, you see the size the file will have to the left below the image. When you have the right size, you save the photo and give it a new name.
If the image is small enough, it can be saved directly using ‘Save for Web and Devices’, where you can set the desired image size and choose Bicubic Sharper in the lower part of the menu options.

[Daisy]

I have just posted some photos on the pest and disease page and they have come out too large. But I have searched all of my Photoshop page and cannot find a crop tool.
I think I must have a different Photoshop.
Can a link to your version be provided?
Thanks, Daisy

[Alisdair]

Sorry, I can't provide a link! (My version is a biggish programme which lives on my computer.) Are you sure there's no crop tool on your version? Try clicking on the Help button and searching for Crop. Or try moving your cursor slowly to each of the little tool icons, one by one, and leaving it there until a short title comes up showing what that tool does.
Or check what version of Photoshop you have, post a message here saying what version it is, and some other Forum member who has that version may be able to help.
If none of that works, you could simply set the size of your photos to a size that would certainly fit on people's screens, say height not more than six inches and width not more than eight, and then go on from there!

[JTh]

When you start Photoshop, the Tools panel appears at the left of the screen.  The Crop tool is number four from the top in the Tools panel, it looks like a square with a line through it, but there are three tools in the same position, Crop, Slice and Select Slice, maybe the Crop tool is covered. You can expand the tools to show hidden tools beneath them. A small triangle at the lower right of the tool icon signals the presence of hidden tools.
You can view information about any tool by positioning the pointer over it. The name of the tool appears in a tool tip below the pointer.
I have copied an image of the Tools panel, so that you can see what it looks like.

[Daisy]

Yes!!!!
I have found it.
Thank-you, both of you, for your help.
Sorry to be such a moron, but my photobucket page, is completely different to your's JTh.
Hopefully, I will be able to post reasonably sized photos now.
Daisy

[Umbrian]

I only have Photoshop elements 2 Can I send photos thro' this programme? I have found the crop tool and used it but, being a real learner on this, cannot discover how many pixels my cropped photo has.

[JTh]

If you right click on the photo (either in your browser or when you look at it in whatever propgram you are using), you will get a list of options, at the bottom you'll find Properties, click on that, and then you should be able to see the dimenions (how many pixels)

[Umbrian]

         Yipee I've done it...posted my first photo thanks to all the help from forum members. I am a complete novice so it is difficult to explain how satisfied I felt! 

[MikeHardman]

At the risk of muddying rather than clarifying, can I give a little tutorial...


There are three things about image size, in terms of file size:
- the number of pixels
- the number of bits per pixel
- the compression (if any)
(the size in terms of inches or cm. is of little relevance)

NB. Each pixel in an image will occupy a pixel on screen, unless scaling or zooming are in effect.


In various places, you can right-click or otherwise find properties that will show the dimensions in pixels.
Say your image is 1000x800 pixels: that's a total of 800,000pixels or 0.8Mp

If your image is in full colour, it probably uses 24 bits per pixel; and since there are 8 bits in a byte (ordinarily), that's 3bytes per pixel. (Black and white images use fewer bits per pixel, higher-spec images use more.)

So the image is 0.8 x 3 = 2.4Mb (megabytes).


Compression

If the file is in a straightforward bitmap format, that will be the size of the file (give or take a little overhead).
But most images we deal with today that are derived from digital cameras are compressed. That requires the use of a format such as JPEG or GIF or PNG or TIFF. JPEG is the most common, and is well suited to full colour photos.
(I know I am ignoring the RAW formats used in higher-end cameras, in association with which TIFF is often used as a master format. Plenty more can be said on that, but not here.)

When saving a file in JPEG format (file extension usually .jpg), various levels of compression are possible. That allows you to save an image with a large number of pixels as a relatively small file. ...Which is good for emailing or posting on websites, or simply keeping your disk space consumption under control. But higher compression means lower quality. A compromise has to be struck. Fortunately it is possible to get very useful amount of compression while barely losing any quality. (But beware saving and re-saving an image many times, as quality will degrade - because typical JPEG uses a 'lossy' type of compression, unlike TIFF, eg..)

So, our example image, which was 2.4Mb in size, could be reduced to perhaps 0.2Mb when saved in JPEG format with moderate compression. The amount of compression achieved depends partly on the nature of the photo; some are intrinsically more compressible than others.


When wanting to make an image file smaller, consider also:

- cropping (reducing the number of pixels by chopping some off the edges)
- the size of the screen the image is likely to be viewed on (eg. my (average) laptop screen is 1,280x800pixels)
- do you need full colour? (A page of black and white text or diagrams does not, eg.)

So:
- crop (eg. in Photoshop or more basic programs such as Paint or Microsoft PhotoEditor) to eliminate extraneous parts
- reduce the pixel dimensions to make the image appropriate for the display system of the person viewing the image (I could suggest limiting it to 400 pixels high/wide, as a rough guide for an image expected to be seen as just part of a web page). But if you expect the viewer to zoom-in, more pixels could be appropriate.
- reduce the bit-depth (change from colour to greyscale or to black and white). (You can usually get by without doing this, and it entails detail than I really want to go into here.)

Our example image file could now be around 50Kb in size.


How do you reduce the number of pixels?

The different image editing programs have different methods for resampling. I can't really go into that here, but in Photoshop: Image --> Resize Image gets you to the right dialog. Always keep the pixel dimensions ratio fixed, otherwise you will stretch the image.

When I resample an image, I usually do not use Photoshop. I find it much easier, certainly for web posting purposes, to use a utility accessible by right-clicking on an image file (ie. a 'shell extension' which gives access to the utility in the 'Context menu').
The one I use now is 'Image Resizer for Windows'. Go to http://imageresizer.codeplex.com and the screenshots will give you a good idea how it works.
Some people will still be using the (perfectly good) image resizer that was available as part of the PowerToys for Windows XP; but has sadly gone from there now.


A good order to do things in:

1. decide roughly what file size you need (may depend on web site stipulations and/or your own preference)
2. check the size of the image file in Mb or Kb (maybe it is OK; it might already have been edited/downsized)
3. make a copy of the original file, work on that (the original serves as a backup, eg. in case you need to start again)
4. crop (reduce image dimensions (pixels) by removing extraneous parts of image)
5. resample (reduce dimensions (pixels) by combining adjacent pixels, using facilities within image editing program)
6. save as JPEG (compress file, moderately)
7. check the size of the file (if necessary, repeat some of the steps but crop or resample more)

(resampling, alternatively, can be done after saving, using right-click utility such as Image Resizer)


I hope that helps!