Using a histogram

[KerryG]

Want to help nail your exposure more often? If so, then you need to learn how to use your histogram. Our new article explains all the ins and outs of the powerful and underutilized tool.

L7 Foto - Using a Histogram

[peterst6906]

Hi Kerry,

Of all your articles so far, I think this is the one that lacks a bit of detail and could be more useful than it currently is.

Don't get me wrong, it's a good introduction and overview, but it isn't all the ins and outs.

As an example, you mention that a histogram to the left represents underexposure and one to the right represents overexposure, where in reality, a low key image will be correctly exposed and still be to the left and a high key image can be correctly exposed and be largely to the right.

That is only glossed over when you mention that there is no correct answer to what a histogram should look like.

Additionally, you mention the issue of ETTR, but you don't give many guidelines on how to achieve it. This is where I think you could provide more guidance and explain that if you shoot and the histogram is centred or left, you can increase the exposure in order to move the histogram to the right. You do that, but some practical examples with images would be really useful.

Also, I think it's worth mentioning that the issue of clipping on the right relates to details that are important. For example, you should let specular highlights clip so that you expose the detail in the image correctly. In the article you mention that you shouldn't clip data, but that isn't totally correct. Underexposing so that you don't clip specular highlights results in poorer images than if you let the specualr highligts clip and then capture the real information correctly.

I also think you mentioned briefly the issue of underexposing and that it is bad in a digital file, but I think this could also be expanded on by explaining the linear nature of a sensor response and the difference in the number of levels within each stop of the sensors dynamic range to show why having something to the left ends up compressing the data into a smaller set of levels and how it is bad for signal to noise level.

Finally, I think if you are talking about the histogram, it's also worth mentioning the highlights warning on most cameras in more detail than currently. In some ways it's better because it's giving a warning based on the linear data rather than the gamma corrected data like the histogram. So the blinking highlight warning is a more realistic indicator of sensor saturation at the specific pixels and is often more useful for RAW capture because the histogram on the camera will show clipping in a histogram, even when there is still room for data (~2/3 to 1 stop) on the sensor. For jpg capture, the histogram rules.

Regards,

peter

[KerryG]

Your points are well taken and I struggled a lot with how much detail to go into with this article. I feel that really learning to use your histogram and blinkies is one of the best tools you can use to improve the number of exposed shots, therefor I am already outlining a more advanced lesson on these topics as this one was really meant as an introduction to using your histogram.

Thank you very much for your feedback and I will be sure to cover all of those topics in the follow-up article.

[blumesan]

Originally Posted by peterst6906

Finally, I think if you are talking about the histogram, it's also worth mentioning the highlights warning on most cameras in more detail than currently. In some ways it's better because it's giving a warning based on the linear data rather than the gamma corrected data like the histogram. So the blinking highlight warning is a more realistic indicator of sensor saturation at the specific pixels and is often more useful for RAW capture because the histogram on the camera will show clipping in a histogram, even when there is still room for data (~2/3 to 1 stop) on the sensor. For jpg capture, the histogram rules.

Regards,

peter

Peter,
I have been under the impression that the highlight warning (on my D200), like the histogram, was derived from the gamma corrected jpeg image even when shooting in RAW. Is this not the case? Does it differ with other camera brands?
Cheers/Mike

[kevgermany]

Kerry, excellent introductory article, thanks. I support most of what Peter said, and your reply. In the follow-up it may be worth considering showing people how to tie in parts/features of the histogram to the subject (eg. peak for sky), which'd help the understanding of high/low key as well as other. I'm not a fan of clipping in camera, prefer to do it in pp. However for jpeg shooters it's really the only way.

[peterst6906]

Originally Posted by blumesan

Peter,
I have been under the impression that the highlight warning (on my D200), like the histogram, was derived from the gamma corrected jpeg image even when shooting in RAW. Is this not the case? Does it differ with other camera brands?
Cheers/Mike

Hi Blumesan,

I've always read that the highlights warning (I alsuse the D200) is from the sensor response, not the gamma corrected data, but now I'm digging deeper to make sure that is correct. I'll pm you when I know 100%.

Regards,

Peter

[Tom Swaman]

Fwimbw, I think you are all partially correct. What I suggest is that this subject needs to be broken down into two subjects, namely Understanding and Using Histograms and Guidelines for Using Histograms to Improve Your Exposure. The former topic is technical first and applications second. The latter topic is practical/applications oriented with simple-to-follow guidelines. If this separation is made for different types of photographers/ photographic interest folks, then the information becomes much more practicable IMHO.

Tom