One
choice that has to be made when taking a digital photo is the file
type. This has a massive effect on how the image is produced.
I think all digital cameras will produce a JPEG. This is a "lossy" format - it is compressed in such a way that some data is always lost. The camera contains
software that will take the raw image from its sensor, edit it to whatever colour temperature has been set (the "white balance"), adjust the brightness and saturation, and leave out some information to compress the result into a smaller file size. The resulting edited data is then saved to a memory stick.
Some cameras offer the option of saving a raw image, containing all the data captured by the sensor. This can then be converted or edited later using either the
software provided with the camera or a third party editor such as Photoshop's RAW plugin. This raw image is the nearest you will get to a negative using a digital camera.
The method used by
Pat and others allows the camera to do the initial editing. A raw image from the same camera would look much different. But the advantages of a raw image are:
- you can edit for the correct colour temperature, brightness and saturation later, using better
software than the stuff in the camera.
- You can go back and do it again later if
still better
software becomes available.
- You have all the data and can save the edited version in a loss-free format like TIFF if you prefer. If you want smaller file sizes, TIFF has the option of using the loss-free LZW compression algorithm.
- You can edit and re-edit withut losing data. If you edit a JPEG and save the result, for example to change the background colour, you are compressing something that has already lost some data through a compression algorithm. A high-quality JPEG can stand that without affecting how the human eye perceives the result, but some can not.
Now, a
good camera with
good software will do a
good job. JPEG compression was defined by the
Joint
Photographic
Experts
Group to look
good to the human eye. If it gives the desired result, I would not quarrel with it. It works for
Pat, and I like it too. But purists should be aware that letting the camera
software do your editing for you, which all JPEGs straight from the camera do, is not a particularly
better option than doing it yourself with different
software.
The Photoshop raw plugin allows a lot of detailed control over how your image is converted ready for editing with Photoshop. Here, as an example, is the nearest I can get to showing a raw image, and the JPEG version produced using Photoshop. (The raw image is as shown by the Photoshop browser, captured off screen by other
software.) The raw version looks like cheese, because of the low colour temperature of the incandescent bulb I used as lighting, but contains all the information I need to produce a true image.
Bill