Dispelling a Myth: Viewing RAW is Impossible

"There is not much sense in RAW viewers - one can't view "RAW images" anyway because RAW is not an image at all".

Yes, how often do we hear this myth: RAW is not an image. This particular misconception is extremely convenient and is often used as an excuse by those trying to explain why it is only natural that most image viewers display embedded JPEG instead of RAW, JPEG-based histogram instead of RAW histogram, and over- and underexposure overlays derived from JPEG previews instead of calculating over- and underexposure indication based on RAW data.

The culprit here is that a JPEG is considered to be instantly viewable, because it contains a "processed image", while a RAW needs conversion ("development"), as it is a "latent image". Well, first of all, a JPEG can't be displayed without heavy pre-processing, more on this later. Second, the time needed to convert RAW is not a reason to refuse displaying it; instead, it is the reason to put some effort into speeding the conversion up.

In fact, RAW is an image, but in a less familiar format. What is said to set RAW data apart from traditional images:

1. "The color on RAW data is wrong"

This is a "color space mismatch" issue.

Every image has a "color space" implicitly or explicitly associated with it, and it needs to be respected. To display an image correctly we need to convert it from the associated "color space" to monitor color space, otherwise the color looks off and may even look funny.

A RAW image is recorded in the sensor's "color space." So nothing is really new here. As usual, all we need to do is assign adequate "color space" to the data. This color space is derived from sensor characterization, pretty much the same way we do it with scanners.

2. "RAW images are very dark"

In fact it is a mismatched Gamma (γ) issue.

RAW images are linear, that is they have γ=1.0 and thus look dark (underexposed) and flat if the correct Gamma γ=1.0 is not assigned to data.

This is not really a difference because any popular image format can be coded with any Gamma value. To display an image correctly, be it RAW, TIFF, JPEG, or PNG, we always take Gamma into account, otherwise the image looks either under- or over-exposed, with wrong contrast.

It is quite obvious that to solve 1. and 2., all one needs is banal color management. It is the same for TIFF files and for RAW files.

3. "RAW data is mosaicked"

Yes, it is most often mosaicked (Bayer pattern RGBG) data, meaning we don't have RGB triplets for each pixel. No big deal. With JPEG images we also do not have full color data at each pixel location; moreover - internally, a regular JPEG does not even contain RGB data. It contains something like YCbCr 4:2:0 data, which needs to be interpolated before displaying. In both cases - either JPEG or RAW - we need to apply some unpacking and interpolation procedures to display the image. However, JPEG is a recognized image format, and thus RAW also should be recognized as an image format.

4. "RAW is open for interpretation; and not a final image"

Well, even more reasons to display RAW for culling.

Generations of photographers have found contact sheets and index prints indispensable -- while contact sheets and index prints do not represent the final photo, they are very useful for culling based on 5 criteria: subject, composition, exposure, focus, grain (noise, if we are in digital domain). Good index prints are not "interpreted" in any way, instead they look a tad dull and undersaturated, as they try to convey everything we captured, from details in deep shadows to details in extreme highlights, without any clipping, compressing, and other artistic tools we apply for final prints.

That's what a RAW viewer is for, too - to allow selecting images based on full information available in RAW data, displayed on your monitor. Not to mention that selecting RAW shots is a task different from processing them, and as such it needs a different set of tools.

In summary, to display a RAW image one needs to use an adequate color space (white balance is a part of this), the internal data format, one must account for linear Gamma, compose RGB triplets, and it is very important to know how to unpack RAW data fast enough to not cause discomfort. That is what we do in FastRawViewer.

FastRawViewer gives you a fast, accurate viewing of the actual image data you captured. No compression, no color gamut limitations imposed by in-camera processing, no deceptive histogram, and all over- and under-exposure warnings right from RAW data.


Adobe Lightroom either displays my Nikon photos as .NEF, supposedly raw files or as .DNG, referred to as digital negatives. So are we not seeing the raw file & its histogram in Lightroom?

When any setting / user control is changed, Lightroom displays the changed histogram, and the image view changes also; while raw data doesn't change. That means that neither the raw data, nor raw histogram are displayed in Lightroom.

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