EOS20 wrote:
Dave Baker wrote
EOS20 wrote
Jpeg throws away pixels ... What pixels would those be, then? When a Image is compressed "In camera" the camera determines which pixels to throw away in the process, These "cannot" ever be recovered!
What Dave was getting at is that JPEG does not actually "throw pixels away." No pixels are lost in the process of making a JPEG.
The JPEG compression process is considerably more complex than implied here. Instead of storing distinct data about each and every pixel, the JPEG algorithm stores generalized data about groups of pixels. It is a lossy format, in that the distinct data for each pixel is not stored. But it does not throw away pixels. Instead, each individual pixel will be described in more general terms. If the compression ratio of the JPEG is very high (i.e., very small files on disk), then a lot of information will be lost and what is retained will be significantly different than the original data. This will be instantly noticeable in the image.
However, if the compression ratio of the JPEG is relatively low (i.e. large files on disk), then the difference between the JPEG-compressed image and the original image will be very small -- so small in some cases that nobody would be able to tell the difference side-by-side to a TIFF converted from RAW with the same settings as were used in-camera.
If you do a 100% Crop of a RAW File converted to a uncompressed TIFF and compare it with a Jpeg image taken streight from the camera you can see how the image has been compressed
No, you can't -- and I know because I've done the experiment myself. If the JPEGs are done in-camera at their highest quality setting (superfine), and the photo is exposed properly in non-wacky color temperature light, the difference between a high-quality JPEG and a RAW file converted to TIFF with the same settings is impossible to see in a side-by-side comparison.
I would set up an experiment to demonstrate this, but all images destined for web display would be JPEGs anyway. You can try it yourself. Take a photo with your camera set to RAW + Large JPEG. Make sure it's a properly-exposed photo in decent light and that the color temperature setting is appropriate. Convert the RAW file to TIFF using the same exact settings in the Canon RAW converter that you had the camera set for to produce the JPEG, then compare the two photos at 100% in Photoshop. Even better would be if somebody else did this part and masked the filenames before you made the comparison, so the test is blind.
But if you plan to do serious editing to the image then it would not be a good option as the more your edit\save a jpeg the more you diminish the quality of the image.
Yes... this is the biggest advantage of RAW over JPEG -- the ability to edit in a non-lossy format. Every time you save a JPEG the data is recompressed. Multiple JPEG saves compounds the loss at each save.