Zone System with ACR - strange result

<p>I'm wondering whether someone can shed some light on a few things.<br>

Background:<br>

When using adobe camera raw, it has been my understanding that the default settings are intended to give your image a little pop, straight out of the box.<br>

By proceeding with the +50% brightness, +25% contrast, and a slight s-curve (etc, etc) I thought that this would not be giving you an accurate (for lack of a better word) representation of your scene and you would be deviating from your metered exposure.<br>

***<br />I created a flat preset in ACR, I zeroed most of the sliders in the basic tab, and selected the linear setting on the curve adjustments and I've been using this flat preset to pre-process (for example) my source images prior to merging to HDRI. So this flat preset is for times when I wanted to minimize any Canon/Adobe 'look' from my images.<br>

***<br />I've recently adopted the Zone system for metering my scenes, and the in camera side of things has been working ok. Today I decided to analyse my photos. This included shooting an 18% grey card (more or less) with no exposure compensation.<br>

Problem:<br>

First step I took in camera raw was to use my flat preset, thinking that this would yield the most neutral of images for me to analysis. In Photoshop I took a colour sample of my grey card but the value was only about 38% (about 96,96,96 RGB), rather than the expected 50% (128,128,128).<br>

This seemed odd so I tried with the default ACR settings with yielded a value close to 50% (128,128,128). This is how it's meant to work as far as I'm aware.<br>

Does anyone know what is going on?</p>

<p>How much of the frame did your grey card fill up? How do you have the metering set up on the camera? This will affect exposure.</p>

<p>The percent isn't the important thing to look for, what you want is matching RGB values. </p>

<p>Once you get the RGB values to match, rather than focusing on the percentages of RGB values, I would recommend that you start using the histogram, you can make adjustments from there. You can find several good videos on YouTube = search for histogram adobe</p>

<p> </p>

<blockquote>

<p>When using adobe camera raw, it has been my understanding that the default settings are intended to give your image a little pop, straight out of the box.</p>

</blockquote>

<p>Not necessarily. If you were to implement for example, proper exposure for raw (ETTR), the default settings would look awful. Adjust and they look great. </p>

<blockquote>

<p>By proceeding with the +50% brightness, +25% contrast, and a slight s-curve (etc, etc) I thought that this would not be giving you an accurate (for lack of a better word) representation of your scene and you would be deviating from your metered exposure.<br /></p>

</blockquote>

<p>Nope, has nothing to do with the actual scene. All the processing in ACR is output referred not scene referred (see: http://www.color.org/ICC_white_paper_20_Digital_photography_color_management_basics.pdf)<br>

Raw is linear data, no equivalent to film which has an H&D curve so be careful here in trying to link the two. </p>

<p>When batch processing through ACR I do two runs: the first I allow ACR to auto-adjust all, the second I set to "default", with all sliders at zero.</p>

<p>I output jpegs with <em>both</em> settings, then review them. Toggling between auto and default version, I decide which I prefer, or if neither is satisfactory, then I'll experiment with settings.</p>

<p>I'll also create a list with the filenames: and note any that use anything other than auto. Finally, I'll delete all the jpegs, run a fresh set with the settings I've decided on, and exit ACR via "Done", to preserve the settings in the program.</p>

<p>With a typical batch the majority I'll just leave on auto, but not all: default will work for some, for some I need to manually play around with the sliders.</p>

<blockquote>

<p>This included shooting an 18% grey card (more or less) with no exposure compensation.</p>

</blockquote>

<p>If this mean you metered off the gray card, that is part of your problem. An 18% gray card needs about 1/2-stop adjustment per the instructions for the Kodak card and elsewhere. See http://www.bythom.com/graycards.htm</p>

<p>The expected 8-bit value for a gray card is 118 for Adobe RGB 1998 or sRGB and 98 for ProPhoto color spaces. Digital cameras are calibrated to a specific 18% gray target and adjusted to obtain the 118 value in the sRGB color space. See the CIPA DC-004 Sensitivity PDF which can be found on the Web. <br>

The reason that 128 is not the expected value is that all color spaces contain a gamma correction. That value is 2.2 for sRGB and Adobe RGB 1998 and 1.8 for ProPhoto.<br>

The CIPA document shows the calculation used to get the desired 18% gray value. To get the ProPhoto value, you substitute 1.8 for the value of gamma. The standard uses a gamma of 2.2.<br>

P.S. I am a digital camera Zone System practitioner.<br>

Allyn</p>

Hi guys

 

Much appreciated for the replies. Thanks

 

@Tudor - approx half the frame was taken up by my A2 sized card. Metering set to spot. In this case aim aiming to

acheive specific values if I can.

 

@ Andrew - Ill have to read up on output and scene refereed. I'm commuting at the moment. What I was trying to

troubleshoot is whether my flat curve was best to use when evaluating zone values in my image.

 

@ Mendal - thanks, I'm usually happy working in ACR, it's just I've never been so pendantic tryin to obtain specific values.

 

@ Curt - interesting, I thought a meter made everything mid-grey - I had a quick scan on the link, and will have a good

read tonight.

 

@ Allyn - that's also very interesting. It's good to know how they calibrate. I'm using sRGB, I had a play with adding some

colour space nodes but I was trying to get my 38% grey to 50%. I'll have a read of that PDF.

 

I'll be back once I've read all this info. This problem came about when I was experimenting to try and meter and acheive

specific values as per the zone system. I want to apply this to colour, helped my my trusty munsell color atlas app. I did

an art course a year ago and I was really interested by the theory of chroma and value. Anyway thanks again. Dave

<blockquote>

<p>What I was trying to troubleshoot is whether my flat curve was best to use when evaluating zone values in my image.</p>

</blockquote>

<p>The raw data or the image as you render it from a raw processor? The correct values are those that produce an image appearance as you desire, I don't see the point of setting sliders that do anything but that. Also see: http://www.lumita.com/site_media/work/whitepapers/files/pscs3_rendering_image.pdf<br>

Rendering the print is a big part of the photo processing and that's what happens in a raw converter when you move those sliders. I don't see how a flat appearing image or one that isn't ideal is useful. </p>

Hi

 

I agree that the flat preset has little value in regular photography but if I'm aiming for specific values on screen then my

thinking is that's a good start?

 

Note: I work as a digital artist, producing 3d environments including texturing and lighting. The purpose of this study is for

both photography and work. I'm interested to see if I can draw attention to particular hues through achieving optimal value

for that hue to reach high chroma, and also vice versa - so I can negate a distracting hue.

 

This can be done with a hue sat, but for me I see the value in understanding this in more detail. :)

Ok, I think I get what's going on....

 

The proper use of the grey card is NOT for exposure, it's for achieving proper white balance.

 

Spot metering is extremely useful in situations where you truly need it, backlight situations is an example. However I

would never use it as a default.

 

What I have started doing is this: In a given light and location intake one shot with a grey card for color balance accuracy.

Depending on the light I will take bracketed shots. Normally 3, but can range up to 10. Some times I just pick the best

exposure, other times I use HDR, but with a natural setting . I'm not looking for that HDR extreme look

<blockquote>

<p>The proper use of the grey card is NOT for exposure, it's for achieving proper white balance.</p>

</blockquote>

Not for shooting raw, that be a spectrally neutral off white. Raw is linear encoded, half of all the data is in the first stop of white (highlight), film and JPEG is not linear, there's a curve (H&D or gamma/TRC). You can use a gray card for raw to WB but it's not ideal and can produce color casts. It's called <em>White Balance</em> and <em>Gray Balance</em> for a reason.

 

Exposure for raw and exposure for the JPEG are not the same. The data isn't the same. The processing isn't the same.

<p>Andrew - interesting point! What do you use to achieve accurate color when shooting raw?</p>

<blockquote>

<p>What do you use to achieve accurate color when shooting raw?</p>

</blockquote>

<p>Raw is <strong>not</strong> a true color image, so that's not possible. This is what a raw file looks like, far from accurate (accurate being colorimetrically correct):<br /> <img src="http://www.digitaldog.net/files/raw.jpg" alt="" /><br /> http://www.digitaldog.net/files/raw.jpg<br /> The question: What do you use to achieve <strong>pleasing</strong> color when shooting raw, is the subject of many books, articles and seminars. Can't be answered until we define the raw converter as a start.</p>

<p>The article on <em>Rendering The Print</em> I referenced above is a must read!</p>

<p>Hi<br>

So after a bit more reading.... I have a headache. :)<br>

I'm aware of a lot of these technical aspects, gamma and the like, but I'm still not wrapping my head arpund it.<br>

First of all, it seems that my camera follows the 12% grey calibration theory i.e. my mid exposures are yielding a 38% grey in sRGB space. This is using the flat conversion in ACR profile I mentioned earlier.<br>

12^2.2 = 38%</p>

<p>I was please to see something that I could make sense of (unless this is a coincidence).<br>

I did a test, shooting 11 images, spanning from -5stops to +5 stops at 1 stop increments with my 5D mk3. The values are in sRGB space, after a flat ACR RAW conversion (!), they are percentages of a greyscale version sampled in PS.<br>

5 <--- -5stops<br>

7<br>

12<br>

18<br>

26<br>

37 <----- this is my mid exposure<br>

48<br>

65<br>

75<br>

98<br>

clipped +5 stops</p>

<p>Do these values make any sense - I can't see how I'd relate this to the zone system. Sorry if I'm missing the point.</p>

<p>Just thought of something.... Is the problem related to the fact that I'm using a 'zone system' with 10 zones, and my camera has a higher dynamic range than the ten zones? so they'll never correlate?</p>

<blockquote>

<p>So after a bit more reading.... I have a headache. :)</p>

</blockquote>

<p>I'll bet! </p>

<blockquote>

<p>The values are in sRGB space, after a flat ACR RAW conversion (!), they are percentages of a greyscale version sampled in PS.</p>

</blockquote>

<p>And differences using ProPhoto RGB? I'll bet. </p>

<blockquote>

<p>I'm aware of a lot of these technical aspects, gamma and the like, but I'm still not wrapping my head around it.</p>

</blockquote>

<p>You don't have to. Tone mapping to taste will make all those zone numbers useless with regards to consistency. Understanding the motivation behind tone mapping as an attempt from memory to put back what the initial Raw preview takes away is part of the creative process. </p>

<p>If you're looking for a turnkey by the numbers process shooting in uncontrolled available light at various contrast, dynamic ranges and exposures, you don't have a sophisticated enough capture system to pull it off. Nobody does, unless you're shooting in the studio.</p>

<p>You might want to start thinking about your camera as just a data collector of photon charged sensor pixel sites that happen to come together as a reasonable facsimile to the original scene as you remember in the form of a preview rendered by software as a starting point for further edits. </p>

<p>I had to adopt this POV and figure out how ACR's editing tools acted on the preview that got me closer to what I remembered of the scene. You have so many rendering options in the Raw space that it's almost the equivalent of sculpting reality or the memory of it.</p>

<p>Look at all the various renderings of the courthouse below I came up with figuring out what a combination of curves and sliders will deliver.</p><div></div>

<p>Reckon <a href="http://topdownvideos.com/training/tone-mapping/">George Jardine's <em>Exposure & Tone Mapping</em> tutorial</a> might be insightful.</p>

<p>David, what Tim and Tomek suggest are spot on. I think you're digging a big rabbit hole here. It be useful if we understood what you're hoping to accomplish. </p>

<p>Very informative video, Tomek.</p>

<p>Did you or anyone gleam from that video a by the numbers turnkey process way of creating a pleasing image without trying to hunt for it in the Raw converter? I didn't.</p>

<p>That video showed a very clear conceptualization of how the numbers relate to the toe and shoulder of film and digital encoding, but I still couldn't figure out a way to remember all that and use it so I can get good looking consistent results. Now I have a headache. ;)</p>

<blockquote>

<p>Did you or anyone gleam from that video a by the numbers turnkey process way of creating a pleasing image without trying to hunt for it in the Raw converter? I didn't.</p>

</blockquote>

George is a friend and associate so I think I can say with some confidence that his goal in this video was simply to attempt to explain what's going on <em>under the hood</em>. Not to correlate that understanding into a user producing a better appearing image per se. Stick with whatever techniques you use to make the image look better.

<p>I know the intent behind that video, Andrew.</p>

<p>My statement was more directed toward getting the OP to try to use the information in that video to create a functional processing system whether there's one to be derived or not. The video actually makes it obvious that George wasn't going to show how to create a pleasing looking image as it relates to mapped zones.</p>

<blockquote>

<p>I know the intent behind that video, Andrew.<br>

My statement was more directed toward getting the OP to try to use the information in that video to create a functional processing system whether there's one to be derived or not.</p>

</blockquote>

<p>Might be a good idea to actually let the OP view the video and ask question if he feels it's necessary, not attempt anything further. <br>

You asked (didn't you)? <em>Did you or anyone gleam from that video a by the numbers turnkey process way of creating a pleasing image without trying to hunt for it in the Raw converter?</em><br>

I provided an answer but then you write<em>: I know the intent behind that video. </em>What then is the point of that post?</p>

<p>I found George Jardine's video to be very well done. He made one point I would like to make in a slightly different manner. There are three Zone Spaces of interest to the Zone System Photographer: The Scene Zones (unlimited), the Camera Texture Zones (found by testing), and the Print Zones (Ansel Adams 10 zones which have so far not changed in the digital world). A digital photographer is either mapping the Scene Zones to a screen image (for the Web) or to a print via Lightroom or its equivalent.</p>

<p>With regard to the values obtained by photographing a gray card, I performed an experiment with two of my cameras (Nikon D800, Sony A7R). In both cases I photographed two ways: First I let the camera pick the exposure in Aperture Priority, ISO 100. Then I used a Sekonic L-758 meter to determine the exposure and photographed in manual mode. The target was a Sekonic 18% gray card produced by Musell Color. Adobe ACR was used to measure the 8-bit gray scale values in ProPhoto color space. The results were interesting: D800 autoexposure 163; Manual exposure 98. A7R autoexposure 67; manual exposure 109. The expected value is 98.</p>

<p>This experiment confirms my belief that only a hand held light meter reading combined with manual exposure mode will yield predictable results when using the Zone System.</p>

<p>With regard to using gray cards for exposure setting, the card is a reasonable substitute for an incident meter only if the card is in the same light as the subject. This is true in a studio but not in general for a landscape.</p>

<p>For my photography, knowing the texture range of my cameras, I meter something whose zone I know or desire and adjust the exposure given by the meter to match that zone. For example, I might meter a highlight such as a cloud and increase the Zone V exposure indicated by the meter by an amount to reach the highest texture zone my camera can record. Thus if my camera's highest texture zone is 7, I would add two stops to the meter reading.</p>

<p>At its most trivial level, the Zone System can be seen as the scientific way to expose to the right. Scientific because you are relying on the measured response of your camera rather than an 8-bit histogram produce by the camera from a JPEG image.</p>

<p>In post processing, knowing that I have captured all the data my camera is capable of, I manipulate the image in Lightroom to obtain the print I desire. This is no different than the original Zone System in which film processing was altered in order to capture the scene range and dodging and burning was used during printing to reproduce the original scene or vision.</p>

<p>I hope these notes help. Absolute numbers are not the goal. Producing a good image is.</p>

<p>Allyn</p>

<blockquote>

<p>This experiment confirms my belief that only a hand held light meter reading combined with manual exposure mode will yield predictable results when using the Zone System</p>

</blockquote>

<p>What about altering the raw processing? For example, for grins, say you upped the exposure 1 stop over what the meter recommended, then after capturing raw, you lowered the Exposure slider about 1 stop. IOW, Expose to the Right and normalize development. You get similar values? See any difference in shadow noise? </p>