"Beware of the histogram display. It stinks."

[codepoet]

first ... the camera's LCD histogram places the metered exposure
for a pure blue screen differently (more to the left) than pure
red or pure green. That is observed when comparing o ev shots for
the three pure colors as well as comparing +3 shots of those
colors. It would seem blue is underexposed by at least 1 stop....
red and green only a partial f stop. One the one hand I'm not
surprised that metering isn't the same, but on the other hand I am
somewhat surprised. [BTW, the highlites flash on all these
monochrome targets ... but have to look again to see if the ev
threshold is different.]

What WB were you using? I suspect that the info from the 1005 pixel sensor is weighted by the WB factors to determine the exposure level.

If we knew the WB that you were using, we could determine how those factors would affect things.

second unexplained observation....as expected, the RGB histogram in
PS Levels shows a small spike on the right edge and large spike on
the left edge for each of these monochrome targets presumeably
saying one channel is blown and two channels are black( these are
the histograms of the created target screens...not the camera
capture of them...maybe I'll will look at that later). Contrast the
multispiked PS RGB histogram with the one-eyed LCD histogram.

What was the exposure length? Is it possible that you are seeing screen blanking or some other monitor affect because the exposure time was too shore compared to some of the CRT tracing going on?

 

[saintj]

While I appreciate Ken Rockwell's enthusiasm for the D70 and a few of his D70 tips lets keep in mind he is the same guy who basically says RAW files are a waste of time... wrong.

photoguy do yourself a huge favor and check out the most knowledgeable person I have found yet , a true D70 expert imho, Thom Hogan. His book is fantastic!

http://www.bythom.com/d70guide.htm

saintj

Reading a review of the D70 by Ken Rockwell, I came through these
writings.

 

[MMuddler]

What WB were you using? I suspect that the info from the 1005

pixel sensor is weighted by the WB factors to determine the
exposure level.
If we knew the WB that you were using, we could determine how those
factors would affect things.

Good question.... Auto WB! Woulda been a better test if I fixed it.

What was the exposure length? Is it possible that you are seeing
screen blanking or some other monitor affect because the exposure
time was too shore compared to some of the CRT tracing going on?

Had not thought of that this morning when I did this!Speeds were 1/40, 1/20 and 1/13 for 0 ev exposures on the green, blue and red screens respectively. No way to tell what the monitor brightness was for the individual color targets so its hard to give meaning to the different metering responses. Again, Blue was significantly to the left of the green and red histograms on the LCD.. The green D70 image has a slight color shift along the bottom edge giving credence to the issue of raster capture. I'll run the test again onite with longer shutter times and fixed WB.

--
Marabou Muddler

 

[codepoet]

Got me too,

I was thinking that CCD sensitivity might be a factor. I have done some tests with a gray card under bright sun. Looking at the raw (uncompressed but also unWB'ed) data from the sensor, all three colors do not have equal sensitivity. Green is the most sensitive, about a full stop more than red. However, Blue is half way in between so that doesn't seem to match your results.

Presumably, you calibrated monitor adjusts for phosphor intensity issues. I assume, there weren't incident light reflections on the monitor.

Hope somebody else can figure it out.

Had not thought of that this morning when I did this!Speeds were
1/40, 1/20 and 1/13 for 0 ev exposures on the green, blue and red
screens respectively. No way to tell what the monitor brightness
was for the individual color targets so its hard to give meaning to
the different metering responses. Again, Blue was significantly to
the left of the green and red histograms on the LCD.. The green
D70 image has a slight color shift along the bottom edge giving
credence to the issue of raster capture. I'll run the test again
onite with longer shutter times and fixed WB.

--
Marabou Muddler

 

[OldSkoOL]

Rockwell is very oppionated which is fine, a lot of what he says is useful but some things he says makes me think. As mentioned he said RAW is a waste of time, maybe for him it is... Perhaps he should explain his reasons more...



--
D70 Knowledge Base, curve downloads, my galleries
http://www.pbase.com/oldskoo1/the_curves
http://nikond70.tk

 

[geneinphx]

While I appreciate Ken Rockwell's enthusiasm for the D70 and a few
of his D70 tips lets keep in mind he is the same guy who basically
says RAW files are a waste of time... wrong.

photoguy do yourself a huge favor and check out the most
knowledgeable person I have found yet , a true D70 expert imho,
Thom Hogan. His book is fantastic!

http://www.bythom.com/d70guide.htm

Speaking of Thom Hogan, I've read through this thread and am quite surprised that no one has brought up this link in regards to his thoughts on the histogram problems of most of the digitals (not just the D70 and not just Nikon.)

http://luminous-landscape.com/essays/open-letter.shtml

Gene

 

[RomanJohnston]

If the historgrm sucks.....just another awesome reason to shot RAW and adjust in post process PSCS where you can see all the channels.

It's all good.

Roman

--
http://www.pbase.com/romansphotos/

http://www.romansphotos.com

 

[saintj]

http://luminous-landscape.com/essays/open-letter.shtml

Gene

Brilliant find Gene, that link had completely escaped me.

saintj

 

[saintj]

Roman how about a run-down on those lenes, look like a hell of a system..

http://www.pbase.com/image/32525769

saintj

btw I see you have that 70 set to 'auto' I'm shocked! ;->

 

[Leon Wittwer]

That is pretty slick. Some cameras, even with color histograms, only flash when the luminance channel blows and don't flash when only a color channel blows.

Leon

Indeed the blinking will occur if only one channel is nearly
overexposed or overexposed.

Since luminance is a weighted average, you can have one channel
overexposed but the average will not exceed its maximum value, and
no pixel will be counted at the far right of the histogram.

Thierry

--
Leon
http://pws.prserv.net/lees_pics/landscapes.htm

 

[Leon Wittwer]

I know, the PSP histogram reads fully blown in whatever colour but
the LCD never flashes! Odd eh?

This likely means that the LCD blows only when the luminance channel blows. I one color dominates, then you can blow out the color channel without blowing out the luminance channel. That is why color histograms are useful, to see blowouts of individual color channels.

--
Dave H
First thing I do in the morning is smile.....get it over with

--
Leon
http://pws.prserv.net/lees_pics/landscapes.htm

 

[kdean]

I don't have a problem with the histogram.

Reading a review of the D70 by Ken Rockwell, I came through these
writings.

"Beware of the histogram display. It stinks. The histogram display
is defective in design and therefore less than useless because its
inaccuracy can lead you to make heinously overexposed images that
still read AOK. The problem simply is that the histogram display of
the D70 (just like the D1H and D1X) only displays the green
channel."

How far is this true? Is this a real problem when you are shooting
in the field? As far as I know, histograms are very important to
check the accuracy of exposures. Then, why did Nikon do this to the
D70 (if what Mr Rockwell says is true!).

I'm no expert, so may be someone may throw more light on this
issue! I've just ordered a D70 and this histogram thing is worrying
me a bit!

 

[Leon Wittwer]

After looking at dave's experiment I started something (intended to
test Dave's no-flashing-highlites result) that gave me some
observations along the way that I don't quite understand
yet......regarding the LCD histogram versus the PSCS histogram
(viewed thru Levels at RGB view).

I see a couple of things described below but i'd be interested in
hearing if you can see them for yourselves with my set up since
I'm not sure if I've messed up...

I created full screen color patches in photoshop... pure red, green
and blue. e.g. red green blue 255,0,0 etc. And then I shot them
on my calibrated monitor with the D70 fullscreen out of focus at ev
+0 and ev +3, +4 and ev +5. I've got Foto's provia loaded.

first ... the camera's LCD histogram places the metered exposure
for a pure blue screen differently (more to the left) than pure
red or pure green. That is observed when comparing o ev shots for
the three pure colors as well as comparing +3 shots of those
colors. It would seem blue is underexposed by at least 1 stop....
red and green only a partial f stop. One the one hand I'm not
surprised that metering isn't the same, but on the other hand I am
somewhat surprised. [BTW, the highlites flash on all these
monochrome targets ... but have to look again to see if the ev
threshold is different.]

Isn't this explained by assuming that exposure is working on luminance? Blue has the least luminance and green has the most.

second unexplained observation....as expected, the RGB histogram in
PS Levels shows a small spike on the right edge and large spike on
the left edge for each of these monochrome targets presumeably
saying one channel is blown and two channels are black( these are
the histograms of the created target screens...not the camera
capture of them...maybe I'll will look at that later). Contrast the
multispiked PS RGB histogram with the one-eyed LCD histogram.

I later created Red Green, RedBlue and Blue Green mixes......
255,255,0 and 255,0,255 and 0,255,255 targets ....confirmed when
looking at individual channel histograms. And I expected to see
the RGB histograms for each of these blended targetss to show a
large spike at the right edge for the two colors that were
saturated and a smaller spike on the left edge for the one channel
at 0. But that observation was only seen for RedBlue and RedGreen.
The BlueGreen combination produced RGB histogram spikes of ????
equal magnitude on the left and right edges. The one black channel
was Red and it appears to have as much weight as the maxed out Blue
and Green channels combined. Hmmm...sure that is easily explained
but that caught me by surprise.

Before i look at the RAW output I want to get past the two issues
above. Any thoughts or explanations?
--
Time to get dressed and go to work!

Marabou Muddler

--
Leon
http://pws.prserv.net/lees_pics/landscapes.htm