Greyscale Test

[Adrienne]

What happens if you take a shot with the lens cap on?

Oh my, I thought you were on to a winner there, but guess what?? 2,2,2!!!

A

[ricktas]

OK, your camera is compensating for the darkness. How do we overcome that? What settings are you using? Is the camera on full manual?

[Adrienne]

Thanks Rick...yep it's in manual, ISO is 100, Auto WB and on f8. I did submit all my RGB readings to my tutor and he said he would accept the 222, but I am a slight perfectionist and I want to know why the camera won't go to 0.

[kiwi]

How are you processing the image?

[Adrienne]

thanks for replying! I am using PS as the Nikon software doesn't seem to give enough info regarding RGB numbers...just histograms.

BTW I hope this doesn't post twice, I thought I replied but I came back to the thread and my reply wasn't there!!

A

[kiwi]

I wonder whether on import the image is being auto adjusted, if you are loading a raw file maybe.

[Adrienne]

Yeh thanks for that but the module notes made sure the settings on PS were on default and the WB set "as shot" and I'm not shooting raw.
I just wish I could get the RGB numbers through other software so as I could compare! Do you know of any other programs with a densitometer?

[arthurking83]

thanks for replying! I am using PS as the Nikon software doesn't seem to give enough info regarding RGB numbers...just histograms.

....

A

Two thoughts on this.

1.(software) Which Nikon software are you using? if ViewNX2(it has to be version 2!!) then the mouse pointer location wil give you a readout of the RGB values in the upper info bar(it may be coloured black if you use the default grey skin)
So if you have the image in the viewer pane, and not just looking at thumnails, just above the image view is a dark info bar, where you toggle on/off the histogram/info box and the pixel view size scale.
So as you move your mouse around the image (in this example on the shadows) you'll see the first two numbers are the pixel location(in the image).. so that as an example values 1024,900 indicate the pixel location on the image starting from upper left corner. The values in brackets are the RGB values for that pixel. PROBLEMS!! (that annoy me). If you zoom in to any of the zoom ratios, the mouse pointer turns into a hand. Great if you want to move the image around for pixel peeping purposes, but makes it hard to 'pinpoint' an exact pixel, or find the darkest shadow pixels. Using the full screen zoom factor on the scale makes it hard to be precise with your mouse pointer.(bloody annoying programming that is!) The hand still works as the pixel locator, but not very precise. ie. it still does what you want it too... but you have to have a lot of patience with it(I never use it for that purpose)
Oh! if you want to view the darkest shadows, press the S key on your keyboard. This shows lost shadow detail. if there is no dark spots on your white background(once you press the S key) you have no lost shadow detail(pressing the H key works in opposition and shows you lost highlight detail)
For that purpose, I use CaptureNX. When you use the histogram tool, click the enlarge icon on the histogram tool(small boat anchor looking widget) makes the histogram larger and hence easier to read accurately.
On the histogram tool, press the small Double Threshold tick box to enable the tick. Entire image shows black and white points on your image, if you have them. If not, once again.. you have no lost shadow detail and no lost highlight detail, you won't see the accompanying black or white speckles in the image. The image should turn grey with lost shadow and highlight details. You can also view the RGB shadow.highlight details by clicking Shift+S(for shadows) and Shift+H for highlights). These are not black/white points, but the colour version of lost shadows/highlight.
To view the pixlel RGB (or black/white points) values, drag the small slider at the bottom edge of the histogram, or simply type in a value in the boxes marked shadows or highlight. So if you type in a value of 5 for shadow detail, and you have the Double Threshold indicator still active, it will then show you the pixels that pertain to a value of 5 or less in black(on the image).
If you click on the 'Watch Points' arrow, the histogram then gives you another feature where you see the RGB values as you scroll the mouse pointer over the image, and you can use a sample area size or a point sample.. eg, you can set it to show pixel values on the pixel your pointer is on, or on an area, 3x3 or 5x5 pixels in size around your pointer. For more accuracy in pixel location, zoom in to 100%, or more, view.

2.(camera)Now! as to why you see no 0,0,0 black pixels.. the only reason I can think of is that Active-D Lighting(ADL) is still enabled in the camera, and possibly in Auto mode. This will try very hard to affect the exposure to the point where it'll try not to produce 0 valued blacks. Of course you still can, but it tries even harder to counter your efforts again.
Now even though PS can't effectively see(or read or understand) Nikon's in camera features, the camera still effectively adjusts exposure to suit it's ADL function, even in Manual mode. It works in degrees of ability.

you said that you used Auto WB. Use manual WB.. any value, but try daylight. Turn off ADL(if it's on) and aperture makes no difference(if you're doing the lens cap test). F/4 and 1 sec exposure with lens cap on will give you only black pixels across the entire image, especially at ISO100.
As a side note, if you use AWB, the camera attempts to balance out the pixel values so that you don't get many lost pixels due to colour balance.
Eg. if in late afternoon sunset conditions, the camera naturally tries to make a scene look more blue that it is, as red pixels blow out much easier than the blue channel does. So for sunset scenes, I adjust WB values(raw images of course) to something like cloudy(with a Temperature value of say 6000-7000K, depending on scene.. and possibly a tint adjustment as well) Doing this then blows the red channel out, and many red pixels are lost(easy to recover with contrast saturation lowering in PP).. But where the histogram initially looked good in exposure terms the processed image now has blown a red channel. Image in camera was too blue. Using AutoWB effective adjusts exposure but in the RGB channel level.. ie. blue pixels tend to underexpose more, so the camera sets a WB value to counter this. Luminance(green channel histogram) effectively stays the same(move a touch this way or that, but close enough to unchanged, even after WB processing adjustments.
Finally just to be 100% sure.. do you have AutoISO disabled as well? Sounds like you have because you can't use ISO100 with AutoISO enabled anyhow.. but it's better to ask than to assume. Default settings is that AutoISO is set to off anyhow.
But the first place to check is the ADL feature.

[arthurking83]

If shooting jpg then the camera is definitely processing the image, before you get it into PS.

Non Nikon software, generally don't recognize any of the camera settings if you shoot NEF mode. ie. thirdparty software allows you to see only the raw data your sensor captured(that's part of my dislike about it, and hence my preference for Nikon software).

shoot raw

[Adrienne]

Phew!! Thanks so much, I have just downloaded NX 2 (I didn't realise I didn't have it, just Nikon transfer.. duh) Just had a quick play with my images and now I am down to 1,1,1. Already an improvement! Tomorrow is another day where I will fiddle with the ADL and the white balance (although the assignment specs were to keep it in auto). AND set to shoot in raw.

Thanks Arthur, I really appreciate your in depth advice!

Merry Christmas to you all, it's been a consuming technical day!

Adrienne

[arthurking83]

..... (although the assignment specs were to keep it in auto). ....

I don't fully understand the Auto mode reasoning, but if you are using any Auto mode, are you allowed to use any user adjustable variables as well?

Auto mode is really no different to full manual mode(if you understand it properly) in that even in Auto mode, you can meter off any part of the scene(using any of the three metering modes available) and use exposure compensation to achieve the exposure you want.
So (I'm only assuming) that the assignment is trying to teach you to achieve a true black point using exposure compensation, as most Auto modes will try to prevent that(and hence give you 1,1,1 or 2,2,2 black points).

There are differences in the types of Auto modes available as well. There are the true Auto modes(Scene types) that set all variables such as shutter/aperture/ and so forth, and then there are the semi Auto modes like Program mode and Shutter and Aperture Priority modes. The semi auto modes only take into consideration the exposure of the scene(as set by you, the operator).

[Adrienne]

I couldn't tell you why they want the camera in auto white balance but the aim of this part of the assignment was to create a zone ruler and learn
the DR of the camera. To help the student become familiar with exposure and pre-visualisation. (?)

[arthurking83]

AH! sorry ... my mis interpretation... WB in Auto... not.... camera in Auto mode! (got it now )