Practice, Hibiscus, no frame, histograph

[JBW]

[xpatUSA]

Nice colors, Brian.

The histograph (sic) looks a bit odd, though.

[JBW]

but at least it's not jammed into underexposed

[xpatUSA]

The histograph (sic) looks a bit odd, though.

but at least it's not jammed into underexposed

Sorry, Brian, wasn't really talking about the shape or even which end it is. I was just a bit bothered by all that spikyness which really isn't obvious in the image itself but seems indicative of some severe post-processing that was not well-handled by the GIMP [?].

[Manfred M]

Brian - I'm with Ted on this one. The histogram you show with your image does not make any sense.

When I copy your image and look at the histogram I get this:




This is much more along the lines if what I would have expected; still a touch underexposed with specular highlights driving the right side of the histogram.

[JBW]

Brian - I'm with Ted on this one. The histogram you show with your image does not make any sense.

When I copy your image and look at the histogram I get this:




This is much more along the lines if what I would have expected; still a touch underexposed with specular highlights driving the right side of the histogram.

Okay, your histogram looks a lot like the one i see in Sony Express and the the figure I see when I adjust levels in Gimp. I am guessing it might make sense not to worry too much about the histogram in Gimp? And i dud adjust the exposure slightly into the underexposed region. You know me and slightly dark shots.

[Stagecoach]

I am guessing it might make sense not to worry too much about the histogram in Gimp?

Hi Brian,

But it may be worthwhile determining exactly what that graph Gimp is showing actually is and its purpose?

[Manfred M]

I am guessing it might make sense not to worry too much about the histogram in Gimp? And i dud adjust the exposure slightly into the underexposed region. You know me and slightly dark shots.

Dark shots - not an issue, but how you get there can make a real difference in final image quality. Deliberately underexposing your shot is definitely going in the wrong direction. A properly exposed image is going to have less digital noise than an underexposed one. When shooting, ideally you want an image that shows neither highlight clipping nor the loss of shadow detail.

In general, we humans are a bit less sensitive to the loss of shadow detail than we are to clipped highlights. So if you can't get a shot where you get into issues on both ends of the histogram, I would opt for a bit of loss of shadow detail. However, there is one exception to that "rule". If what you are are clipping are specular highlights in the image, these can legitimately be clipped without getting too concerned. Often these reflections are localized reflections of sunlight and I would be tempted to let these slip through in order to give me more shadow detail (and exposure) into the image.

If you want a darker image, then adjusting the gamma, adding a vignette or dodging the affected areas is the better way to proceed. I don't know how Gimp works, but in Photoshop the black point, white point and gamma can all be adjusted with either he levels controls or with curves.

[xpatUSA]

Brian, Manfred, a bit of loose terminology going on here. In the OP I see "Value" selected for the histogram but in Manfred's I see "RGB".

Here we are, "Value" and "RGB" histograms as shown in the Show Image utility:



But the GIMP histogram is still spiky, no idea why . . .

[Manfred M]

Brian, Manfred, a bit of loose terminology going on here. In the OP I see "Value" selected for the histogram but in Manfred's I see "RGB".

Here we are:


But the GIMP histogram is still spiky, no idea why . . .

Ted - I have very limited experience in Gimp, so haven't got a clue as to what it is doing. In Photoshop, I can display and manipulate each colour channel separately or handle the entire set of RGB values at once. In normal work, I will look at each of the channels separately to see where I clipped or lost shadow detail. The global RGB adjustments is fine for setting the black point, white point and gamma.

[xpatUSA]

Originally Posted by xpatUSA Brian, Manfred, a bit of loose terminology going on here. In the OP I see "Value" selected for the histogram but in Manfred's I see "RGB". But the GIMP histogram is still spiky, no idea why . . .

Ted - I have very limited experience in Gimp, so haven't got a clue as to what it is doing. In Photoshop, I can display and manipulate each colour channel separately or handle the entire set of RGB values at once. In normal work, I will look at each of the channels separately to see where I clipped or lost shadow detail. The global RGB adjustments is fine for setting the black point, white point and gamma.

Hi Manfred,

In the GIMP on my computer the histogram for the first (downloadable) image in the OP is similar to yours, i.e. without all the spikes and drops in the OP:



I can only conclude that the review image in the screen capture in the OP is not identical to the one actually posted.

[jcuknz]

The image as posted has a pretty even histogram with rather more[higher] in the b;ack end reflecting the dark foliage while the first thing which I noticed [ and looked for as I had a similar problem with a bright yellow locomotive ] was the excessive brightness of the left petal and using curves I simply dragged the centre point down and to the right, just a little way which improved the saturation of the whole flower.
Bearing mind my error with the previous flower where moving the white point to the end of the representation got a brighter punchier image it was not correct according to what Brian wanted ... so my conclusion is to watch the monitor and do not blindly follow the histogram and the final result should come from editing rather than in-camera adjustments resulting in an incorrect exposure.

I tend to believe with Ted that the histogram shown is not that of the image posted. Being a content measurement of the bright green foliage and the bright petals?

[JBW]

Okay folks this morning I went out and worked for half an hour or so to get the best looking in camera histograph I could get. Nicely balanced, no spikes and the shot looked good too. When I uploaded to Sony Express it still looked good. When I transferred it to desktop it looked good. When I opened it in Gimp... ugly.

Now before we annoy a moderator for talking about post processing in the wrong forum I will be posting the relevant information in the proper forum in a few minutes. Unless the thunder storm closes in.
B.

[Manfred M]

Okay folks this morning I went out and worked for half an hour or so to get the best looking in camera histograph I could get. Nicely balanced, no spikes and the shot looked good too. When I uploaded to Sony Express it still looked good. When I transferred it to desktop it looked good. When I opened it in Gimp... ugly.

Now before we annoy a moderator for talking about post processing in the wrong forum I will be posting the relevant information in the proper forum in a few minutes. Unless the thunder storm closes in.
B.

Brian - the histogram is not something you design, but rather gives you information about the image. I look at the file coming out of the camera as my raw material for image processing, regardless of which of the various file formats that my camera delivers (jpeg, tiff or raw) I end up using in post-processing. There are three pieces of information I draw out when I look at a histogram.

1. Is my exposure good? Generally I am looking for underexposure as that is a primary cause of digital noise in my end product. If I get a shot that technically overexposed, but does not show any signs of highlight clipping and I bring things back to the way I want them to look in post, this is called "Expose To The Right" or ETTR. I will occasionally shoot this way on purpose as it helps further reduce digital noise.

2. Am I losing shadow detail? When there is data at the "0" position (all the way on the left hand side) of the histogram, it shows how much pure black there is in the image, i.e areas of no colour. The occasional spot of pure black is not going to make a lot of difference in an image, but larger areas of pure black do not look that good.

In general, most photographers would prefer a small areas of loss of shadow detail rather than having highlight clipping.

If I do get blocked shadow detail, I may also be interested in which colour channel this is occurring in.


3. Do I have blown highlights in this image? In most instances, blown highlights are something most photographers will try to avoid, especially in skies, because this can look terrible in the image. There is really one exception to this; specular highlights, which are areas of reflected light. As an example whitecaps on waves are one area where nothing can really be done to eliminate them.

As with the blocked shadow detail, I will examine individual channels to see which one is blowing out.

[JBW]

Brian - the histogram is not something you design, but rather gives you information about the image. I look at the file coming out of the camera as my raw material for image processing, regardless of which of the various file formats that my camera delivers (jpeg, tiff or raw) I end up using in post-processing. There are three pieces of information I draw out when I look at a histogram.

It was a lot simpler when i was working ion instinct.

But as long as the teaching keeps flowing i will keep on chopping away at it.

now that just might be a mixed metaphor?
Brian

[Manfred M]

Every good, experienced photographer I know works on instinct; BUT they also use the tools at their disposal to ensure that things are working the way they should.

[xpatUSA]

Okay folks this morning I went out and worked for half an hour or so to get the best looking in-camera [histogram] I could get. Nicely balanced, no spikes and the shot looked good too. When I uploaded to Sony Express it still looked good. When I transferred it to desktop it looked good. When I opened it in Gimp... ugly.
B.

Nice detective work there, Watson. I've only just recently downloaded the GIMP and have yet to get to grips with it. I feel that you are on the right track and will await your post in the other forum.

Meanwhile it may be that, in the GIMP, the actual on-screen pixel size of the histogram is affecting it's rendering, especially it's width. Please bear in mind that calculation of counts for each level is for 0-255 levels. Therefore, the "perfect" width for the x-axis is 256px and next-most perfect will be 512px. Anything else and there will the dreaded interpolation involved. And never go below 256 wide, even though the histogram window's width can be adjusted.

In more advanced histograms such as RawDigger or ImageJ you can actually set the bin width, e.g. one vertical count bar in a 16-bit histogram could be set for 8 levels.

[JBW]

Nice detective work there, Watson. I've only just recently downloaded the GIMP and have yet to get to grips with it. I feel that you are on the right track and will await your post in the other forum.

Meanwhile it may be that, in the GIMP, the actual on-screen pixel size of the histogram is affecting it's rendering, especially it's width. Please bear in mind that calculation of counts for each level is for 0-255 levels. Therefore, the "perfect" width for the x-axis is 256px and next-most perfect will be 512px. Anything else and there will the dreaded interpolation involved. And never go below 256 wide, even though the histogram window's width can be adjusted.

In more advanced histograms such as RawDigger or ImageJ you can actually set the bin width, e.g. one vertical count bar in a 16-bit histogram could be set for 8 levels.

You obviously have a good understanding of the technical side of pp. This could make coming to grips with Gimp a lot easier than a newbee like me found it. I do know that after two years I am still finding better ways to do things in Gimp. have fun.