4

With Canon 650D (and presumably all the other Canon), I noticed that the picture style and full JPG processing is used to generate a review JPEG which is what the camera actually reads when reviewing images through the LCD (and actually, most RAW capable image viewers are using this thumbnail as well).

The problem is, assessing the image through this review JPG and its histogram which has varying degrees of contrast, saturation and exposure tweaks as well as a tone curve and other processing elements I just have no idea about, has resulting in my misjuding of the exposure in the RAW file, leading to over/under exposed images. Clearly these embedded JPG have their benefits; the camera need not reprocess the RAW to show you the review, when the camera gets it roughly right you can be lazy and just extract the JPG and use that.

So, how can I get my camera to show me something in the review image and histogram that is as close as possible to the actual RAW data I will have to work with?

  • See also What is UniWB? – mattdm Oct 12 '14 at 3:37
  • If you're worried about exposure, is not a histogram view what you want? – Patrick Hughes Oct 13 '14 at 14:53
  • @PatrickHughes yes, but the histogram is the histogram of the embedded JPEG after the camera has applied its rather aggressive (in my opinion) tone curve. – user1207217 Oct 14 '14 at 20:53
  • @user1207217 I totally forgot about that after-processing part, I spend too much time with film. Thanks for the reminder for the thread! – Patrick Hughes Oct 15 '14 at 3:03
5

You can use Magic Lantern to display RAW histogram in live view and image review. Head over to http://www.magiclantern.fm and download the version available for your camera. The installation instructions are different for each camera and can be found in their forums.

In order to view RAW histogram in the preview, you could shoot with the technicolor cinestyle picture style, or any other 'flat' profile.

Magic Lantern also has a ton of other features that will aid you in setting the right exposure, like zebras, warning dots on the histogram and an auto-ETTR mode (http://en.wikipedia.org/wiki/Exposing_to_the_right). It is slightly complicated, but definitely worth exploring.

  • I edited the answer to point out that RAW histogram is also available for image review. – user1207217 Oct 16 '14 at 21:41
  • Even then, the histogram displayed using Magic Lantern has the curves applied for whatever picture style you have selected. – Michael C Aug 2 '15 at 17:02
  • The "raw" data used for Magic Lantern's RAW histogram feature is from the low resolution video feed, not the full resolution raw data. – Michael C Mar 6 '17 at 1:22
13

You can't view a RAW image, because a RAW file is not an image, it is a set of monochrome luminance values. When the data is converted to RGB using demosaicing certain settings such as contrast, saturation, etc. are applied. There has to be a value for those settings. You are much better off learning to use the histogram (also drawn from the JPEG preview) to judge exposure rather than looking at the brightness of the LCD screen. A perfectly exposed image can look grossly overexposed if the LCD screen is at the brightest setting when you are in a darker environment, and I suspect this has more to do with your exposure problem than which picture style is selected.

The closest you can probably get to what you want is to select the neutral picture style. But be aware the images will look flat until you add some contrast, saturation, and work your light curves in post processing.

Here's an image of a scene with a very wide dynamic range when rendered with some highly customized light curves and +1.17 stops brightness adjustment to raise the shadows and then reign the highlights back in a little.
customized curves
Here is the same RAW file rendered with a fairly standard set of curves: the neutral picture style and no brightness adjustment.
neutral curve
Here is the same RAW file rendered linearly (no curve). The reason the gamma correction line is curved (in the shape of a near perfect curve for y=(√2)^x when x is between -10 and +4) in the histogram is because the exposure stop scale is exponential - there is really twice as much distance between each set of two stops as you move to the right as there was between the previous two stops. If the exposure scale were rendered that way, then the response "curve" you see would be a straight diagonal line.
enter image description here

I think it is obvious why the camera makers do not allow images to be rendered linearly on the rear LCD screen. But notice that the shape of the histogram is identical in the neutral and linear conversions. It is the response curve that has changed. Also notice that the very small totally saturated area is not very accurately indicated at the right edge in both the neutral and linear gamma correction histograms.
Closeup of the linear histogram.
histogram

Here is the final edited image after some additional, fairly aggressive tone mapping has been applied using Canon's DPP HDR module to the single RAW file as originally edited with the customized light curves.
enter image description here


Addendum (In response to comments below by user1207217)

Based on the following images, it is fairly certain the histograms rendered in DPP from raw files are based on a non-gamma corrected, linearly rendered TIFF preview embeded in each .cr2 file created by a Canon EOS camera.

The small (160x120) JPEG thumbnail preview: JPEG preview
There is also a full size JPEG preview image embeded in each .cr2 file that appears to have the exact same processing applied as the thumbnail, other than the obvious resizing.

And the slightly larger (592x395) TIFF preview (rendered as an unedited jpeg): TIFF preview
You can view the actual TIFF here.

  • 3
    I know I can't view a RAW image, which is why I asked "close as possible to the actual RAW data I will have to work with". In addition, I use the histogram, but the histogram is the histogram of the embedded JPEG and not of the RAW data. I tried various picture styles, but all of them are invariably blowing highlights that are not actually blown in the RAW, presumably because of some agressive tone curves in the camera processing. – user1207217 Oct 11 '14 at 20:55
  • 1
    @user1207217 "How can I make camera LCD show true RAW image?" – Michael C Oct 11 '14 at 22:30
  • And the rest of the question body? :) – user1207217 Oct 12 '14 at 2:21
  • And the last paragraph of the answer.... – Michael C Oct 12 '14 at 12:29
  • 1
    You still don't seem to understand. The 8-bit per color channel display on the back of your camera is not capable of displaying the 12-14 bit RAW files generated by a modern DSLR. There must be light curves applied and white and black point set before you have a viewable image. If you are that concerned about precise exposure of highlights, then get a light meter and use the zone system. – Michael C Oct 12 '14 at 12:35
2

Your best option is probably using the "Neutral" picture style, this will apply minimum processing with a flat tone curve and no sharpening.

This will give you the closest thing to a raw histogram available in-camera but it will make the jpeg look dull and lifeless - so you'll lose the ability to use the jpeg and preview for anything except judging focus.

  • I'm sorry but I can't agree - the tone curve is not flat and I am still finding an exposure (and contrast!) difference between a completely neutral RAW file and the Neutral style JPG extracted from said RAW file. With Neutral style changed to minimum contrast (-4) the exposure gets closer but even still there are contrast differences and midtones are pushed considerably (0.5-1 stop). Maybe the picture styles differ between Canon models? – user1207217 Oct 12 '14 at 12:26
  • 1
    How are you defining "completely neutral RAW file?" There is no such thing that can be displayed on a 24-bit (8-bit per color channel) monitor! It has to be converted and a light curve applied. If you use a "linear" response (some convertors will let you display one) you will get the nastiest looking dark image you have ever seen, but it is still converted to 8-bits toi be displayed on your monitor. – Michael C Oct 13 '14 at 6:22
0

I think that using the Neutral style and configuring the camera to use Adobe RGB instead of sRGB would give the closes possible representation for the "original RAW", but it's actually not anywhere near. And depending on the RAW processor you use, it could still be very different (LR process RAWs very differently than the Canon software, and so on).

Anyway, for burn-out zones and so on, the best option would be Adobe RGB color space.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.