Here's a page on how computers store images. It's useful to be familiar with the idea of what image compression entails. Remember that 'JPEG' compression is lossy - every time you save an image as a 'jpeg', it's damaged - hopefully in ways you won't be able to see.
Repeated saves will reveal incremental damage though ...
Picasa and your images
'Picasa' respects original images, in that it refuses to change the image data in files it finds.
At first, this seems strange, considering that its purpose is to be an image editor. Picasa is actually following best practice here.
Think of it like this. You might have an old shoebox full of family photographs, with negatives. 'Picasa' would regard those negatives as important - they were actually there when the photographs were taken. Nothing has more information about the event they record.
Similarly, a first generation image file on your hard disk will have more information than any derivative. 'Picasa' respects that to the extent of making your life quite difficult if you try to change one of these images - with the following exception.
Adding metadata - a.k.a. 'Writing on the back of the photograph'
Picasa allows you to store a description of an image, embedding this in the image file - in fact you can store a description, and also keywords, as iptc data - a standard for data that can accompany an image within the file itself. Picasa 3 also correctly handles xmp metadata.
Digital cameras use iptc data to store information about the camera and its settings as well - sometimes this information can be useful when processing the image.
The upshot of this is that descriptions you add to the image are there for keeps (or until the image is edited using incompetent software) and this is very valuable when the image parts company from the person that knows it. Picasa uses this information in various ways - but you can also view it by choosing Properties from a right mouse click menu on an individual image.
Picasa makes use of this information in several ways:
When you view an image, you'll see an invitation to 'Add a caption' beneath it. Picasa then silently stores this information in the image file itself and copies them to any of its children.
When you're viewing an image, use the keyboard shortcut 'Control' and 'k' to add iptc keywords to your image. Again, this information is immediately saved to the image file itself - the advantage being that, like writing on the back of a photo, the information persists, and when the image is moved, the information goes with it.
Note that Picasa's 'Labels' are not (yet) stored as iptc data ...
So how does Picasa edit image files?
It doesn't. Instead, it displays the original image file. and keeps a note of the changes you make, editing the display accordingly. It only changes the actual file when you save or export it - and even then it hopes to make a backup of the original.
What Picasa doesn't do
You can't use 'Picasa' to edit images pixel by pixel - it's not an image retouching tool. Update: Picasa 3 now includes 2 additional tools - you can retouch an image and add text. When text is added, you can 'Show and hide it' too.
Hints and tips
Add other locations to Picasa's library
When you install Picasa it will search your whole disk, should you ask it to. You can also ask it to search other locations - use the 'File/Add folder to Picasa' menu item. You can ask it to search just the once or to keep an eye on changes
Search for images
Picasa searches on file names and on captions and keywords - this is particularly good if you've actually added these of course!
Full screen view
When you're scanning through Picasa's library, hover over a single thumbnail and press 'Control' and 'Alt' to fill the screen with an individual image.
Use Control and 'k' to add any number of keywords to an image's itpc data.
Add a caption
When you're viewing a single image, look below the image and select 'Make a caption' to add a description - like the last, it's immediately saved to the image itself.
Add a label
Right mouse click an image and add a label - make up a label on the spot if you need a new one, otherwise pick from a list of previously used labels. Picasa 2.5 doesn't save this data with the image but future versions will surely do so.
Make sense of Picasa's file view
This isn't easy sometimes - but in the 'View' menu, it's possible to choose a 'Flat file' view or a 'File tree' option ...
If you've a series of images that need similar edits, proceed as follows. Pick one, edit it as necessary, and then, with the image's thumbnail selected, go to Picasa's menus - use 'Edit/copy all edits'. The second step is to select the other images that need similar edits and use the menu 'Paste all edits'.
When you're ready to take an image elsewhere, display it in Picasa and then from Picasa's menus select 'File/Export picture to folder'. You can select appropriate quality settings and you can resize the image if you need this ... see below
Resize images using Picasa
You can resize an image to the size of your choice, but you may need to know how to set the size.
The starting point is to export the image from Picasa using the menu 'File/Export'. You'll see a dialogue that allows you to set the quality of the jpeg that you'll produce - here's a page explaining image compression.
The dialogue also allows you to set the size - which immediately makes you wonder whether you're setting the width or the height! The answer is that Picasa is setting the length in pixels of the longest side of the exported image - so if the image is 'Portrait' in format, Picasa allows you to set the height, if landscape, the width.
If you're exporting a portrait format image but need to set the width, you'll need to do some arithmetic to find the figure you need to set in the 'Resize' dialogue...
Picasa: resize a 'Portrait' image to a set width
When you ask Picasa to resize an image to a particular size, it resizes the longest side. Often, you need to resize a portrait photo to a specific width - use arithmetic:
Display the image in Picasa. Look below it and make a note of the width and height of the existing image
Divide the figure for the image's existing width by your final intended width. The result should be greater than one - we don't want to be 'Upscaling' images
Divide the 'long' dimension of the original image - the height - by the result from the above
What you'll have then is the figure you need to use in Picasa's file export dialogue to give you the width you need.
Picasa: online image size calculator: this form runs the calculation for you:
Do you need to size a landscape image to a specific height? Just use 'Width' for 'Height' and sling the values ...
Once Picasa's installed, you can use it to produce graphics for Minerva, for web pages etc. Picasa will convert images from say Windows bitmap or bmp to JPEG format too. Here's how.
You can use Picasa 3 to 'Improve' an image, crop it, remove blemishes and finally export it as a jpg. Once you've installed Picasa, upload images to your pc and Picasa will index them.
'Improving' your image
Once its opened in Picasa, use the various tools to edit the image if needed. You can do this quickly and Picasa displays any changes immediately - you don't need to save copies as you go, Picasa displays changes as an overlay - without editing the original.
Picasa 3 has a text tool. Type words onto your image and then drag on the placement tool and you can quickly adjust the position and size. You can also rotate the text.
Cropping your Image
Picasa's crop tool has a variety of preset dimensions.
Minerva Course Banners
If you need a banner image for a Minerva module, use Picasa to crop it as follows. Select 'Manual' and aim to produce a 'Long thin image'. Don't worry about the dimensions of the image in pixels at this stage, but when you export the image from Picasa (see next) choose a value for the size in pixels of around 500 pixels - this will produce a banner that fits in Minerva's workspace.
Minerva staff photos
Minerva requires these to be 150 by 150 pixels - when you have a photo of yourself that you find bearable, use Picasa to crop it to square format. When you come to export it, set the size to 150 pixels.
Now includes a useful slider. It's good to use a sharpening tool after all other processing.
Exporting the result
When you're done, use Picasa's menu 'File/Export' to save a copy as a jpeg. You'll need to select the image size and quality.
Size: Picasa gives you a single value in pixels for the size of the image. The image is likely to be rectangular, Picasa is referring to either width or height whichever is greatest. See above ...
Quality: set this to 'Normal' which compresses the file, but with minimal effects on the image itself. This is fine for a web site or for Minerva.
All before you, in this world, is smoke and shadows.All before you, in this world, is smoke and shadows. Words found on a door lintel in the garden of a house in the Cretan village of Argiroupolis. The lintel is a fragment from the city state Lappa, which occupied the same site. Fifteen hundred years later, when you use the web, from time to time you might well feel that the author was on to something. And if you work with particle physics, you'll know he was ...