Help needed with curves

Dick on Aruba

Here’s a picture that seems to have a “correct” exposure. Using +1.00 EV did make a histogram-shift to the right without blowing the highlights.

Here’s the picture:




Reading the RGB histogram from left to right, you notice that everything is well within the luminosity range. Here’s the RGB histogram:




The individual RGB histograms are also (from left to right) within the luminosity range but they peek well above the 255 reading them from bottom to top:

Red Curve:




Green curve:




Blue curve:




Is this, exposure wise, a bad thing and if so, what can I do to prevent this?

Personally I can't find the "bad" in "blowing" the 255 range on top of the histogram.



The picture without +1.00EV or undone any in camera modification will give
the same results and, of course, I shoot NEF.

[FONT=&quot]Dick.[/FONT]

Duffy Pratt

I'm not positive, but I think you are misreading the implications of the vertical component of the histogram.

The horizontal component is divided into 256 intervals, each representing one of the possible tonal levels in an 8 bit picture. The vertical component shows how much of the image has that particular level. When it goes over the top of the graph, it just means that the amount of the picture that lies in that tonal range falls outside the graph's ability to represent it. But that doesn't mean that anything is blown out.

If the entire scene were completely blown out, with no detail at all, then the histogram would show a straight line at 255 and nothing else. Similarly, a shot of total darkness should show a straight line at 0 and nothing else on the histogram. And a shot of an absolutely evenly lit grey card should have a single spike somewhere in the middle of the histogram and nothing else.

I hope this is clear. I'm pretty sure that I'm right about how histograms work. What I don't understand is why you are so worried about the histogram when the exposure is so obviously correct. If the histogram did say otherwise, that means something is wrong with it, not the exposure.

Duffy

jfriend

Peaks in the middle are not bad

Duffy Pratt wrote:

I'm not positive, but I think you are misreading the implications of the vertical component of the histogram.

I agree, I think you've got it right here Duffy. The vertical scale in the histogram s ONLY a measure of how many pixels are at that particular luminosity value. A tall steep and extremely high peak in the histogram that is not at the left or right edge just means that there are a lot of pixels in the image with the same luminosity. That's a characteristic of the subject and, as long as the peak isn't at the far left or far right edge, there is nothing you can or should do to change that with exposure settings. At the extreme, a properly exposed picture of an evenly illuminated white piece of paper would show one very tall spike in the histogram because the whole image consists of so few discrete tones and there's nothing wrong with that - that's a proper recording of the real scene.

Dick on Aruba

Duffy Pratt wrote:

I'm not positive, but I think you are misreading the implications of the vertical component of the histogram...

The horizontal component is divided into 256 intervals,...

... What I don't understand is why you are so worried about the histogram when the exposure is so obviously correct...

Thanks Duffy.

I think you're right.

I understand that the amount of pixels (botton to top) in a certain luminosity (left to right) may exceed the 255 range but I was not 100% sure. The Ron Reznick SureShot DVD's was not very specific about the vertical range but very detailled about the horizontal range.

Worried? Not really but "assumption is the mother of all fu....." Right!

Thanks again.

Dick.

Dick on Aruba

jfriend wrote:

I agree, I think you've got it right here Duffy...

Thanks John.

I feel better, It confirms that I did understand the histogram and was not living in assumption that I know something.

I was able to "nail" an exposure, I did not find any fault in any picture that was justifying the exeeding of the vertical 255 range. So...

It's always better to ask.

Dick

Jeanne Marie

I think I understand this as reading that the majority of the tonal range in the image lies in the midtones, spiking at the gray shows very little contrast. This is just how I understand it to work.

jfriend

That's right

Jeanne Marie wrote:

I think I understand this as reading that the majority of the tonal range in the image lies in the midtones, spiking at the gray shows very little contrast. This is just how I understand it to work.

That's right. This image has a fairly low dynamic range with not much distance between the brightest and darkest tones. Likewise, the tones that it has are concentrated in a fairly narrow range right near the middle. This is fairly common for images taken in full shade with no significant pure white or black items in the image. I find it's also common for images taken outdoors on a heavy overcast day.

This isn't bad. It's just the way the image occurs in nature. Sometimes these images gain more pop by adding contrast to them in PP (push in ends with levels or curves and/or add an s-curve). And, sometimes they just start to look unnatural when you do that because the eye knows what to expect. It varies by image and intended result.

rosselliot

do you know if you can adjust curves on photoshop elements?

how?

- RE

jfriend

Curves in elements 4

rosselliot wrote:

do you know if you can adjust curves on photoshop elements?

how?

- RE

Elements does not come with curves support. You can use levels to set the whitepoint and blackpoint in Elements and you can use the contrast adjustment to achieve something similar to an S-curve for enhanced contrast, but neither is quite as powerful as a curve.

There are some 3rd party add-ins that give you curves in Elements. There were a bunch for Elements 3, but Adobe made it a lot harder to offer curves in Elements 4. I've lost track of what works for curves in Elements 4 (I used to use Elements 3, but now I use CS2). Perhaps someone else who has figured this out in Elements 4 can chime in.

A quick Google search shows this dgrin thread on the subject and this flickr discussion about the same program.

Jeanne Marie

I applied levels and curves adjustment layers and applied some selective sharpening to get this. It could probably use some saturation adjustments and other tweaks, but the information is all there to work with.

jfriend wrote:

That's right. This image has a fairly low dynamic range with not much distance between the brightest and darkest tones. Likewise, the tones that it has are concentrated in a fairly narrow range right near the middle. This is fairly common for images taken in full shade with no significant pure white or black items in the image. I find it's also common for images taken outdoors on a heavy overcast day.

This isn't bad. It's just the way the image occurs in nature. Sometimes these images gain more pop by adding contrast to them in PP (push in ends with levels or curves and/or add an s-curve). And, sometimes they just start to look unnatural when you do that because the eye knows what to expect. It varies by image and intended result.

Dick on Aruba

Jeanne Marie wrote:

I applied levels and curves adjustment layers and applied some selective sharpening to get this. It could probably use some saturation adjustments and other tweaks, but the information is all there to work with...

Thanks for your suggestions.

I posted this almost unprocessed picture just as a sample. The "final" was actually posted on my SM account a good while ago and look like this:



As you can see that this is much closer to your suggestion than the almost unprocessed one in my first post...means to say that you're not far off.

The peeking vertikal curves...well...I was looking more for a confirmation than for an answer actually.

Dick.