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How to read the histrogram
Over and over from the good photographers I read, "CHECK the HISTOGRAM". Well maybe not so strongly put but ok, I've seen the light. How do I read the chart on the back of my Nikon? Can some one briefly explain or point to a good tutorial? The word "histogram" is used so often that search functions here (and in Google) are not much use. The D-70 owners manual tells me how to find the chart but not how to read it. I understand that a lot of area off the chart is not a good thing. Are there zones for Red Green and Blue? Does the chart read right to left? Is the subject one so deep I should hold the question for the photo class I'll take when I leave my day job for the much longed for retirement?
Thanks in advance and please don't take offence the off the cuff comments. I prefer to use JPEG large because I do not enjoy the post production work. I’m sure a good understanding of this subject will improve my work.
Thanks in advance and please don't take offence the off the cuff comments. I prefer to use JPEG large because I do not enjoy the post production work. I’m sure a good understanding of this subject will improve my work.
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Start with this article at Luminous Landscape, then maybe this one at Nikonians.
I do glance at my histogram frequently. I'm generally looking only at the ends of the histogram for underexposure or overexposure.
- If you see a gap at the right end of the histogram, you are underexposed and should increase exposure until the histogram gets near the right edge (without making a spike at the right edge).
- If you see a spike at the right edge of the histogram, it usually means you are overexposed and you should reduce exposure until the spike goes away. The spike is a bunching of values all at 255 which means you have clipped the data and lost detail.
- If your camera's histogram shows you the individual color channels in the histogram, that is even better and you make sure that none of the individual color channels are clipped.
- If you see a spike at the left edge of the histogram and the histogram goes all the way to the right edge also, that means that have a high dynamic range scene (more range than the sensor can record). The spike at the left edge means you have shadows with no detail. At this point, you have to decide what is more important in the shot (highlights or shadows) and optimize the exposure for that, sacrificing the other.
The shape of the histogram in between the ends has no right, wrong or correct shape. It's just a characterization of the distribution of tonal values in your image and different images will have different distributions. I am just looking at the ends.Homepage • Popular
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Basically, what the histogram is supposed to show is a distribution of tones recorded by the camera. In order to avoid "clipping"* an image and provide the best exposure, you want to keep the tones close the right side of the histogram without actually going too far to the right.
I find the histogram plus the highlight "blinkies" to be the best way to expose in the field. You want the histogram to the right and without the blinkies in the image. (Unless there are areas of the image that don't need detail. In that case, blinkies are OK in the areas without detail.)
Once you deviate from daylight, you need to pay special attention to the histogram as the tonal distribution becomes "biased" in one color direction or the other.
This is where it is extremely important to review your images with software histograms, especially software that can display separate RGB histograms.
Where you see the histograms pushing both the left and right sides, the tones are probably beyond the ability of the camera to record in a single exposure. In that case, either decide which tones are most important (shadow or highlight mostly) and adjust your exposure accordingly to capture those tones, or use multiple bracketed exposures and HDR technique.
I have a few examples of different histograms here:
http://www.dgrin.com/showpost.php?p=666259&postcount=9
Just keep in mind that the combination of "shoot (the histogram) to the right" combined with no (or very few) "blinkies" will generally yield the best exposure unless the scene has too much dynamic range for your camera to record in a single exposure.
*Clipping is defined as those areas which lack detail.
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There is not RGB histo's on the D70. I'm not sure of the exact term (luminosity?) but I think of it as a graph with the horizontal axis being 'brightness' of a pixel going from darkest to brightest, and the vertical axis being a count of how many of those pixels.
Let that sink in a minute, then apply it to a photograph.
So if you're out on a sunny day and you intentionally overexpose a frame (say a 1 second exposure on ISO 400 f/8.) When you look at the picture in the screen you'll notice it's almost completely white (if not completely white). Therefore you'll expect the histogram to have a ton of bright pixels, and virtually none that are dark. So your graph should be VERY heavy on the right of the histogram. (Heavy on the right of the histo is tell-tale blown highlights and overexposure).
Alternatively you're out taking pictures of fireworks. You've got it dialed in perfectly and the histogram shows a ton of pixels counted in the dark end (left) and just a little sliver on the top end. However you know this is OK because counting the pixels there are a ton that are black/dark and only a few where the light from the 'works hit the sensor.
Going deeper....
Now slice the histogram into 3 vertical sections, evenly spaced (there is a setting to turn this on/off on the D70 - it's called 'grid' I think.) The middle slice is where the action is, and where you want (on a normal day - not fireworks) to find the majority of your pixel count. The section to the left are your 'shadows' and to the right your 'highlights' (you should recognize these terms from your favorite image editor.) A normal, outdoor, sunny picture of the dog should look something like a mountain with it's peak in the middle section of the histogram.
Now consider & diagnose...
If the mountain shifts to the right, that means you're losing highlights - overexposure.
If the mountain shifts to the left, that means you're losing shadows - underexposure.
& the tricky part...
The A # 1 thing I look for is to make sure there are never high pixel counts at either extreme end of the histogram. When you see this it means it has exceeded the dynamic range of the sensor. When this happens image subtlety is thrown out the window. Instead of a dark brown the sensor sees it as black, or instead of summer lime green the sensor sees white. Here you have to make a decision, is it ok to blow a highlight in this frame to make the important part well exposed?
Consider... you're doing a portrait of a very dark-skinned individual wearing very light clothing, say a white t-shirt on a bright sunny day. Is it super important to correctly expose the shirt so that the wrinkles and other nuances are visible, or is it better to overexpose the shirt (blowing highlights) to correctly expose the face? Obviously, blow the highlights and get the face, 100% of the time. [on a side note, this is a great time to use you're exposure adjustment tool - the +/- button - to make a quick, simple adjustment without having to take a ton of test shots to dial in.]
Lordy I hope this made some sense... Good Luck!
"Your decisions on whether to buy, when to buy and what to buy should depend on careful consideration of your needs primarily, with a little of your wants thrown in for enjoyment, After all photography is a hobby, even for pros."
~Herbert Keppler
John