Want to know how the image is captured and saved to your camera? Want to know what JPEG stands for? Then read on.
When it comes to taking photos in the JPEG format, versus taking photos in the RAW format, there are huge differences. Below, I’ll just discuss how an image is captured and then the difference in the file formats. In a future article, I’ll graphically show you the differences in the image quality of these two image formats.
After getting a better understanding of JPEG versus RAW, you may want to upgrade to a camera that saves it’s images in the RAW format…or not.
JPEG vs RAW
You have surely heard of images saved in the JPEG format, but have you heard about camera images saved in the RAW format? About 99.9% of you have cameras that save images in the JPEG format – if you have a cell phone that takes photos, you have one – if you have a point-and-shoot camera, you have one – and if you have a pro-level camera, you have one. You may have noticed that when you look at your image files on your computer, they have the file extension .jpeg or .jpg, like ‘filename.jpg’.
But, do you have a camera that captures images in the RAW format? Yes, you do if you have any camera at all. All cameras capture their image in a raw, unaltered format. But, that doesn’t necessarily mean that the image is ultimately saved in one of the raw image formats. For most people, this is just fine.
DIGITAL CAMERAS HAVE A SENSOR
Here’s what happens when you press the shutter button on any digital camera. The image is captured on a sensor (in the old days, film would be waiting for those light rays after they passed through your lens – today an electronic sensor is waiting for those same light rays), like the one at right that’s in my camera.
And here you can see the sensor (the greenish-blue thingie), when the lens is removed, as it sits in my camera.
See ‘Size Matters’ below for a short discussion of camera sensor megapixels and their importance.
As soon as you snap your photo, that sensor, along with the computer chip in your camera, now passes color information along the camera’s electronic pathway.
WARNING: Don’t want a bit more technical information? Then skip the next paragraph.
Each pixel on the sensor is made to respond to either red, green or blue light (but not all three) and there are 2 green-sensitive pixels for each red and blue pixel, because human eyes are more sensitive to green. I don’t want to muddy the waters much more, but there is another important step in here: a process called ‘Bayer interpolation’ calculates what the ‘true’ color of each pixel should be based on the relative strengths of the red, green and blue neighboring pixels. Each pixel in the converted image now has three color factors stored for each-and-every pixel: the red intensity, the blue intensity, and the green intensity. The brightness of the pixel is also stored for each pixel. The mixture of those three colors for each pixel gets converted into color intensity for each of the typical colors, be it red, yellow, green, cyan, blue, magenta, or the millions of colors in-between.
So, the computer chip within your camera has now determined which color each of the pixels should be, along with their intensity, and that color information is now transmitted along the camera’s electronic wiring to the next step.
CAPTURING THE IMAGE
Once that color intensity information has been calculated, it is passed to a computer chip that is installed in your camera. But, before it reaches that chip, it is in a raw, unaltered state – this raw image has not yet been saved to the storage device in your camera (a ‘card’ for many cameras, or typically a built in storage device within your cellphone). So, just before that image reaches that computer chip in your camera, the image is in a raw format. If you were able to see that image at this point, trust me – it would not be very flattering to you as a photographer, as it is very dull in several ways.
Another really cool thing is that a lot of other information travels along with that captured, but as yet unsaved, image. Information such as the camera model, date, time, lens and camera settings, and location (on some cameras, but for sure on your cellphone camera). That information will be stored in the image file down the pipeline as explained below.
So, what happens next to this raw image? That’s where the computer chip in your camera does some marvelous things. What that chip does was determined several years ago by a group of camera-industry folks who started to meet in 1986. They called themselves the Joint Photographic Expert Group (the acronym for which is JPEG – cool, huh?!). In a 1992 meeting, they all agreed that the raw, unprocessed, unaltered, unadulterated and non-manipulated image that the sensor captures had to be enhanced if the masses were to ever buy a digital camera.
The JPEG agreed on the following: the raw image should have the contrast increased a certain amount, so the image doesn’t look so ‘flat’; the raw image should have the saturation increased by a certain amount, to give it more ‘color’; the raw image should be sharpened a certain amount, so it doesn’t look so ‘fuzzy’.
Another factor that is adjusted is the ‘white balance’, which is a bit more difficult to explain in a short article; but, suffice it to say that it has to do with whether the overall look of the photo is warmer or cooler, and is directly related to the settings you can make using your camera’s menu for ‘scenic’, ‘portrait’, ‘shadows’, ‘tungsten’, 'flash', etc.
They also came up with a way to save the photographic image so that it would take up less space on your storage device, which means that an image saved as a jpeg image loses just a bit of its quality each time it is saved.
So finally, the sensor information with the JPEG-designated changes, as well as the camera and capture information mentioned above, is baked into the file with the file extension of .jpg as it is saved to your camera.
So, when you press the button on your camera, the sensor captures the light rays, the electronic version of those rays is sent through your camera’s wiring to a computer chip in your camera, then that chip manipulates the image using the Bayer calculations and standards created by the JPEG folks, and finally it is saved to your camera’s storage device. You then just look at the image digitally, print it out at home, upload it to a print facility, or take it personally to a print facility.
If you want to have prints larger than the usual 4”x6” variety, you may or may not have much luck getting a quality print – as the camera’s sensor size is one of the factors that determine print-size quality. Again, see ‘Size Matters’, below.
Here is a simple flowchart showing the process just described. The flow along the top is the one to generate a JPEG file. The blue line below avoids all of the JPEG's enhancements, as discussed next.
SAVING IN RAW FORMAT
If you have a more expensive camera, like a digital single-lens reflex (or DSLR), or one of the new mirrorless cameras with interchangeable lenses, then that camera most likely can actually save images in a raw format. The file extension (instead of .jpg, for instance) is .nef for Nikon, .cr2 for Canon and .arw (among others) for Sony, etc. Most of the cameras just mentioned can also save images in .jpg format instead, or at the same time (i.e. two different file-format images are saved at once to the storage card).
And further, even though one may just intentionally be saving images in a raw format, there is also a small .jpg image being created and saved (whether you want it to or not – and you do, by the way) for display on the back of the camera. Yes, that image one sees on their DSLR camera back is a jpg image that sits in another file alongside the file for the raw image.
SO WHAT, YOU SAY?
OK, if you are satisfied with cellphone and point-and-shoot photo quality, saving images in the .jpg format, stick with it. If you are interested in pursuing a higher-level of photography, then you will want (actually, I’d say ‘need’) to capture and save your images in the raw format.
Why? The files saved in the raw format that you will be working with have tons more information with which to work, which I will demonstrate for you in a follow-up article. In other words, the raw files are not limited to the fixed enhancements that the JPEG manipulation bakes into the .jpg files.
The down side? You will have to manipulate every image using software (like Adobe’s Photoshop or Lightroom) to get to a satisfactory .jpg image to print yourself or to send away for printing. That means that you will need to touch every image to even get it up to the same quality as the JPEG’s criteria of the less-featured cameras.
In the case of your cellphone camera or point-and-shoot camera, the sensor is much, much smaller than this one shown at the beginning of this article. And being smaller, the files that are saved are much smaller. If you tried to blow up a photo to a large size using an image from your cellphone, it would look quite ‘blocky’ and have very little resolution. As a quick guide, generally speaking, a camera that captures images at 3 mega pixels (or 3mp) will create a decent print of only 5”x7”. If you have a camera that captures its images at 10mp, you could print an images at 9”x13”. My Nikon D800 camera has a 36mp sensor that creates images that can be printed at 16”x24” with no additional manipulation needed. So, size does matter when it comes to camera sensors and how large you want to print an image.
As mentioned above, if you want to get into photography at a more-serious level, you should consider a camera that can save images in the raw format, and then invest in the software and time to manipulate those raw files. If you are satisfied with what you have, stick with it.
I will show you what I mean by 'having more to work with' in a raw-image file in an upcoming article.
Ciao for now,
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