JohnFrim Loc: Somewhere in the Great White North.

This post is not about whether to shoot RAW or JPEG. That issue gets beaten to death enough, and it will never be resolved until manufacturers decide not to provide the option in-camera and force users into saving in a single file format.

Rather, it is about clarifying some of the terminology associated with digital photography, primarily for newcomers but also for film-days old timers who have made the transition, so that we might all speak the same language. I am hoping this post will help preclude misunderstandings such as what appeared in a recent thread where a poster thought he was perhaps turning a JPEG into a RAW file because he was able to open and manipulate the image in RAW editing software (LR, if I recall correctly).

To begin let's clarify that RAW and JPEG (along with PNG, TIFF, etc) are storage file standards or specifications that essentially define/describe how the binary pixel brightness data from the sensor are organized in the file, so that an image processor (or printer) can convert that data into something viewable on the computer (or on paper). And since these terms are file specifications, technically the "thing" that one sees on the computer or on paper is neither RAW nor JPEG, nor PNG, nor TIFF, etc.

So my question to the photo or computer technophiles is, "What is the correct term to describe what one is looking at on the computer screen when examining a digital file?" I don't know if there is a specific term, so I will just use the term "image" for the remainder of this post.

I use a Mac, and when I use the Finder to look at my folder contents I see thumbnails of my ".JPG" files but just an icon for the ".ARW" files. I suspect the finder is "too dumb" to extract the JPEG thumbnail from the RAW file. But even lowly software such as Preview will open the RAW file and present me with an image, and I can use the rudimentary editing tools in Preview to make adjustments to the image and save the result as TIFF, PNG, PDF, JPEG etc. While the original RAW file was about 17 MB and the corresponding SOOC JPEG was just over 5 MB, the TIFF is over 128 MB, so clearly the richness of the data varies between file formats. But regardless of what format I save in, I am still seeing the same "image" on my screen.

Of course, more sophisticated editing software will show thumbnails of both file types and will open both for editing. The point I am making is that RAW and JPEG merely identify which file was used as the source of the data that is being displayed as an image on my computer.

Going back to the camera, my Sony has an EVF, so I am seeing a WYSIWYG presentation of what my image might look like on my computer. Of course, I can set the camera to save the data as RAW, JPEG, or both, but what am I really looking at in the EVF or on the rear screen? Am I looking at a visual presentation of the JPEG as it will be stored, or could I be looking at the RAW? If I set the camera to store only RAW, am I really looking at a presentation of the RAW, or am I seeing the JPEG that is automatically embedded in the RAW? I suspect the camera is limited, just like the Finder on my Mac, to dealing only with the smaller JPEG data.

What about cameras that don't use an EVF, but may allow live view as an option and certainly provide in-camera review of the images? I suspect they, too, are just presenting the image as derived either from the JPEG that is embedded in the RAW file or from the JPEG that is specifically designated as a storage format.

In any case, it boils down to understanding that one is never really looking at a RAW or JPEG file directly; rather, the computer or camera is using one of those files as the source of the data to present an image to the user.

So I ask again, is there a technical term other than "displayed image" to describe what one is looking at, or do we just leave it that?

JF

twowindsbear

Maybe qualify further as 'displayed image' and 'printed image?'

rmalarz Loc: Tempe, Arizona

John, "displayed image" is quite good. It describes what you are being shown after software, either in camera or photo editing, determines what to show you.

The differences between file formats is quite a bit different. jpg is a lossy compression algorithm, tif is not, but can be depending on the save options one chooses within editing software.

The myriad of different image formats would require reading the specifications of each to determine the quality of image one would get by saving to any of those. I, personally, am more familiar with jpg and tif as those are the two with which I deal most of the time.

gif images are quite good for illustration, comic strip for example.

Again, the "preview" image is derived from the RAW data the camera collects upon actuation of the shutter. This image is subject to the coding embedded in the camera to translate the RAW data into a preview image. Image editing software has its own translating coding to render the jpg preview image from RAW data.

The save as function in editing software has the necessary algorithms to translate the data to other formats. So, if you have a jpg image, for example, and want to save it as a tif, the software has the necessary translating code to do so.

I hope this answers some of your questions. If not, let's carry on the conversation.
--Bob

rebride

Raster graphics image.

Ol' Frank Loc: Orlando,

All of this stuff is way over my layman's head, however I understand and appreciate the term "displayed image" and will just use that.

jcboy3

"Displayed image" is a well used term for the visual presentation of an image.

Most image formats have a direct translation into a "displayed image" (e.g. JPG, TIFF, PNG). The contentious point of discussion about RAW formats is that there is a lot more processing required to generate a representative "displayed image". Some image viewers will do minimal processing, without performing optical or color corrections. But in general the RAW images are converted to an intermediate format before displaying them.

In addition, RAW is a generic term; each camera manufacturer has its own image format (e.g. NEF for Nikon, ORF for Olympus, and so on). So the specific comparison is between JPG and a particular RAW format such as NEF.

All RAW formats that I am familiar with contain an embedded JPG image that is created by the camera with the specific camera settings used at the time the picture was taken (picture mode such as "vivid", white balance).

As far as the ability to view the images on the Mac, perhaps this is another specific RAW format issue. The RAW formats I use are displayed as icons and preview on the Mac just like other formats such as JPG.

JohnFrim Loc: Somewhere in the Great White North.

Bob, my intent was to have an informative conversation for the benefit of readers, not just me, and the devil is sometimes in the details.

Maybe I am splitting hairs here, but you said that "… the "preview" image is derived from the RAW data the camera collects upon actuation of the shutter. This image is subject to the coding embedded in the camera to translate the RAW data into a preview image. Image editing software has its own translating coding to render the jpg preview image from RAW data." You are implying that previews in-camera are decoded from the RAW data, but I was under the impression that a RAW file has an embedded JPEG (Edit: just saw another post from jcboy3 that confirmed this), and it was that JPEG that gets displayed on the camera display. It does not matter in the end, but I do like to be technically accurate. So, do you know for certain that the camera decodes the RAW for preview?

Going back to your other posts in which you showed a rather off-color image that you PPed to look fantastic ( :thumbup: ) did the display on the camera also look like the greenish posted image (which is a JPEG)?

brucewells Loc: Central Kentucky

John, for Windows machines, we can download and install codecs that allow the Windows Explorer to display thumbnails of the images, instead of an icon. I have to think it is very similar for Apple machines, but I don't know.

While Nikon and Adobe both provide codecs for their particular file formats (Canon and others probably do, as well), there is a very inexpensive product named FastPictureViewer ($10-15) that will allow the display of all formats. I've used it successfully for years.

Hope this helps someone.

Apaflo Loc: Anchorage, Alaska

Pretty close!

There are actually two parts, one is a "data format" standard, the other is a "file format" standard. Often they are very tightly linked and hard to differentiate. But the TIFF standard is a good template to learn the concept as it is well differentiated between the two. For example almost all RAW file formats are actually the TIFF file standard, but have nothing to do with TIFF data formating standards.

Incidentally raw sensor data is not image data, but RAW files (thanks to the TIFF format) are able to store the raw sensor data and one or more JPEG formatted image data sets that are used for previewing.

Its kind of like saying that a bucket is a device for storing/carrying things. We can fill it with milk, oil, or with water. Or we can compartmentalize the bucket by carrying bottles. The bottles might have water or milk in them, and both can fit in the bucket at the same time.


Absolutely correct. What the computer does is extract a data set from the file. It has to know about the file format, and it also has to know about the specific data format. So it reads data from the file and then that data is converted to a data format computer can use directly.

Note that with a RAW file that is not image data! The sensor data, once stored in computer memory has to be interpolated to get one specific image. But any one set of raw sensor data can correctly be interpolated to nearly infinite number of specifically different images. Image data specifies only one image. Raw sensor data specifies a set of sensor data, not an image.

With a JPEG, TIFF, GIF or PNG etc data set the image data is converted to perhaps an intermediate format for a given program. Each editor, as an example has it's own format. But just for display it is converted to what might best be called "RGB image data", because virtually all printers and monitors use RGB formatted data. That is not necessarily true though, and there are printers that use CMYK data, vector data, or perhaps something else.

But "image data" would be a (very loose) term that covers them all, and "RGB data" fits what is usually meant.

And you are absolutely right that it is not TIFF, RAW, JPEG or whatever. Ideally when viewed on a monitor the "RGB data" from any given image would be exactly the same regardless of which format it had been saved to a file in, but that is only true with lossless compressed files and merely close to true when lossy compression is used.


This brings up another can of worms! Encoding efficiency is different for different data formats.

The RAW data, which once again is not image data, encodes color using the Bayer Color Filter Array method and an exact color is not recorded and also the color for any specific location is distributed over data from multiple locations and the "key" to which location is not stored in the data, but is determined by an externally stored pattern of the data. That is why a RAW sensor data file is so much smaller than a TIFF image data file. The TIFF file is storing an exact color for each location and there is nothing kept external to the file. But it won't compress as well as JPEG does either.

Computer data encoding, like encryption and compression, is not something an average photographer needs to understand. It's a distraction that prevents learning photography!

Rongnongno Loc: FL

Couple of comments...
1) raw is NOT a standard
2) What a camera displays on the view finder is a highly compressed JPG sampling* of what has been captured if after the fact. During the live preview this is a compressed video sampling.

When viewing a 'raw' from anything but an editor you only view then embedded JPG, never the raw file itself. The quality of the embedded JPG is set in camera by your own JPG quality selection. What this mean is really you do not need to shoot raw + JPG. (do a test - change the JPG setting and capture the same scene).

It gets worse... Some editors were using the JPG not the raw and of course reduced the quality to 8 bit...

----
* A camera histogram is based on this sampling. One of the reasons it should not be trusted especially when 'shooting raw'.

dsmeltz Loc: Philadelphia

"Displayed image" is irrelevant. It is rooted in what can be shown right now. A raw image has data which may or may not be "displayable" right now in a single screen. A RAW file has more than that. A RAW file has future potential that is not limited by your narrow view. So I disagree with your premise that these formats are "storage file standards or specifications that essentially define/describe how the binary pixel brightness data from the sensor are organized in the file, so that an image processor (or printer) can convert that data into something viewable on the computer (or on paper)." That limitation misses the point entirely. Just because your current display or your current program cannot produce a fully realized image does not mean that the full potential of a RAW file should not be preserved.

Apaflo Loc: Anchorage, Alaska

The in camera generated "preview" image is a JPEG.

It is of course interpolated and then formatted as a JPEG by the camera from the raw sensor data. But it's use beyond that, whether on camera preview or during post processing preview displays is just the same as viewing any other JPEG image.

Bill_de Loc: US

"Rather, it is about clarifying some of the terminology associated with digital photography, primarily for newcomers but also for film-days old timers who have made the transition, so that we might all speak the same language."

Really? :roll:


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rmalarz Loc: Tempe, Arizona

John, to answer your question, yes, the preview looks like the SOOC image. Which is also the reason for my comment in one of my posts that the histogram and chimping are pretty much useless to me.

If you case you care to read some additional information regarding the technique and principles used for that initial image, I have the original article I wrote located here:

http://www.uglyhedgehog.com/user_page.jsp?upnum=1527

--Bob

JohnFrim Loc: Somewhere in the Great White North.

Well, that's certainly what I was hoping. So far I think the conversation has been informative.

For example, I now understand the subtle distinction between data format and file format; I now appreciate that sensor data is not image data per se; and I will never again call RAW a standard.

I fully get it that some folks are not interested in low level details, and if they refer to the displayed image on their computer screen as a JPEG I can live with that. Similarly, I can overlook F16 vs f/16 for aperture even though the latter is technically correct and makes it clear why f/4 lets more light enter the lens compared to f/11. There are, however, some folks on UHH who present themselves as experts and speak with an air of authority, yet they are clearly wrong in what they are saying, often due to the incorrect use of terminology. The point of this post is to raise awareness about terminology because when taken out of context it could lead to false interpretation.

I consider myself quite knowledgeable in several technical areas, but I am here to learn as well as share, and I really appreciate when someone points out where I am wrong, especially where accuracy in terminology enhances clarity and understanding. I hope at least some others feel similarly and are being helped by this discussion.