Month: September 2009

Nikon D700: RAW and JPEG Files Compared

JPEG is an image file format recognized internationally by cellphones, computers, and other devices.

RAW is an image file format that is sometimes called a digital negative because it is relatively unprocessed. It is proprietary to each camera manufacturer and in contrast to JPEGs, RAW files are not recognized by cellphones, computers etc.

All digital cameras produce RAW files, but many digital cameras – particularly small point-and-shoot cameras – do not allow the user to download the RAW files from the camera.

Instead, the camera processes the RAW files into JPEGs internally, and only the JPEGs can be downloaded or extracted from the camera.

JPEGs can be produced from a number of file formats, not just RAW files. Whichever file format they start with, in the process of saving the files as JPEGs they discard pixels that are identical to others.

The software makes a note of where the discarded pixels are and rebuilds the file when it is re-opened.

JPEGs can be saved with finer or coarser compression. The coarser the compression, the less discrimination the file uses when it discards pixels, and the smaller the size of the compressed file.

Most if not all digital single lens reflex cameras (dSLRs) however, do offer the option to download the digital negative from the camera. A number of compact cameras also allow the user to download the RAW files.

The RAW files can then be processed using an external RAW conversion program.

There are several such programs on the market, including some free ones. Nikon and Canon for example, make programs for use with their own proprietary RAW files.

Photoshop™ is a RAW conversion software program. Photoshop does other thing as well, of course, but at its heart it is a RAW conversion program. It can convert the RAW images to a number of formats, including Photoshop documents (PSDs) and JPEGs.

Why do photographers bother with RAW files when they can get the jpegs straight out of the camera?

The reason is that the color palette of RAW files is finer that that of JPEGs. That is, it has finer gradations or transitions of tone and color. This gives photographers more leeway to make changes to the image.

The JPEG algorithm cannot discriminate such fine gradations of color, so in the process of compressing and saving the files, it discards some pixels that are subtly different from the ones it keeps.

Altering JPEGs can lead to posterization, which is what happens when the color loses its smooth tonal transitions and breaks up into bands of color. It does this because the intermediate colors are lost in the process of altering the image.

Why would photographers want to alter images? Well there are many reasons, but one common one is so they can adjust the exposure after the event.

That is sometimes necessary or desirable because the photographer or the camera doesn’t always get the exposure right.

Adjusting exposure to brighten up the RAW file in Photoshop or some other imaging editor is likely to produce a better final image than trying to do the same thing to a JPEG.

On the other hand, if the photographer can get the exposure right in the camera, he or she can let the camera convert the RAW file with its own internal RAW processor, and have a JPEG ready to use.

I almost always shoot RAW because I like to be able to correct my mistakes work with the original digital negatives.

This past weekend however, I used a new camera, a Nikon D700, for the first time. One of the options the camera offers is to shoot a RAW image and a fine quality JPEG simultaneously.

And that gave me the opportunity to see whether there was any difference between a JPEG straight out of the camera and a JPEG from a converted RAW file.

I didn’t alter or sharpen either image, so there was no question of the JPEG being degraded by processing.

Here is the full frame of the converted RAW file. And below it are two crops from the full frame. The first is a crop from a converted RAW file and the second is a crop of a JPEG straight from the camera.

Can you see a difference in the quality? Is one sharper than the other? Is the color of one better than the other?

What do you think?

Cheviot Sheep

Jpeg from RAW file

Jpeg from camera

The full-frame image is one of a series from the Masham Sheep Fair 2009 article.