Project 2: Digital image qualities
Exercise 5 - Sensor linear capture
I have spent a lot of time trying to figure out how to change a jpeg to 16 bits/channel, as suggested in the course material. I am using Photoshop Elements 7 and going through (Image>Mode>) does not offer me an option to convert to 16 bits, only 8 bits. After asking in forums and trying to figure it out from my book, I shall presume that it’s not possible, and continue the exercise without converting it. I have also found the example curve missing from the course material here.
So, let’s get started:
To adjust colour curves, I go into (Enhance> Adjust Colour > Adjust Colour Curves>)
I have spent a lot of time trying to figure out how to change a jpeg to 16 bits/channel, as suggested in the course material. I am using Photoshop Elements 7 and going through (Image>Mode>) does not offer me an option to convert to 16 bits, only 8 bits. After asking in forums and trying to figure it out from my book, I shall presume that it’s not possible, and continue the exercise without converting it. I have also found the example curve missing from the course material here.
So, let’s get started:
To adjust colour curves, I go into (Enhance> Adjust Colour > Adjust Colour Curves>)
Picture 1: The original
Picture 2: Here the colour curves are adjusted to imitate what the image would look like before the camera’s processor works on it. It is therefore imitating a linear capture. The image is darker and in the histogram the tones are squashed to the left.
Picture 3: Here the colour curves are adjusted to imitate what the camera’s processor would do. This image is lighter and the histogram is more similar to that of the original picture.
The side effect in lightening the image as in picture 3, can be that noise is exaggerated.
The side effect in lightening the image as in picture 3, can be that noise is exaggerated.
What I also have learnt from this exercise is that adjusting the curves, changes the appearance of the histogram.
Exercise 6: Highlight clippings
In this series of photographs, the second image contains an exposure where highlight clippings just appear. In the following photos the exposure has been decreased by one f stop at the time.
In this series of photographs, the second image contains an exposure where highlight clippings just appear. In the following photos the exposure has been decreased by one f stop at the time.
1: 1/60 sec - F/6.3
This is the best image as the colours are saturated and the sky appears clearly. I think the image could be improved further if the colours were saturated in Photoshop. Click here to see my attempt. |
As the exposure increases, the visual information of sky is lost, and the colours are overall less saturated, they appear bleaker. Michael Freeman discusses the topic highlight clippings on his blog. He finished with the exclamation "Clipping is good - discuss!" as they might say in an exam.
I think we have be aware of clippings and how to avoid it. But even though stock agencies would reject a clipped image, we might sometimes want the highlight or shadow clipping to exist. Photography should be more than just measurement of the histogram. It's every photographer's artistic right to include clippings, even though it mighn't be appreciated by everyone. It's important though to know the rules on how to avoid clippings, before you can break them.
I think we have be aware of clippings and how to avoid it. But even though stock agencies would reject a clipped image, we might sometimes want the highlight or shadow clipping to exist. Photography should be more than just measurement of the histogram. It's every photographer's artistic right to include clippings, even though it mighn't be appreciated by everyone. It's important though to know the rules on how to avoid clippings, before you can break them.
Exercise 7 - Your tolerance for noise
The following images have been taken at different ISO settings to examine of ISO effects noise in the picture. The noise reduction has been set to off in all images.
The following images have been taken at different ISO settings to examine of ISO effects noise in the picture. The noise reduction has been set to off in all images.
Exercise 8: Camera dynamic range
In the first image I meter the brightest point, the white paper, using the spot metering setting in the camera. In Photoshop, I measure the brightest pixel value, and the value is 240.
1/4000 F 6.3 |
In the second image I meter the darkest point in the shadow in the hall way. The darkest pixel value is 15
1/125 F 6.3 |
How do I calculate the difference in f stops between 1/4000 and 1/125? As I turn the “wheel” on the camera it goes: 125, 160, 200, 250, 320, 400, 500, 640, 800, 1000, 1250, 1600, 2000, 2500, 3200, 4000. Does this mean that the dynamic range is 15 f stops? No, because I have counted the clicks on my digital camera and I should be counting according to the scale of the old mechanical days, which halves all the way down. Each stop lets in half the amount of light:
4000
2000
1000
500
250
125
This means 6 f stops between 4000 and 125. If a top end DSLR has a dynamic range of 9-10 stops, a 6 f stop range for my entry level DSLR seems plausible.
4000
2000
1000
500
250
125
This means 6 f stops between 4000 and 125. If a top end DSLR has a dynamic range of 9-10 stops, a 6 f stop range for my entry level DSLR seems plausible.
Exercise 9: Scene dynamic range
Out of a series of photos with different exposure, this shows details in the shade and only contain only a slight blown hightlight in the clouds. I prefer losing some visual data in the white clouds, and keep the area in the shade visible.Using the spot metering, I measure the brightest point to be 1/800 at f6.3. The darkest point in the shade was 1/25 at f6.3. This means a dynamic range of approximately 5 fstops.
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This image contains the highest contrasts in this exercise and can be described as a high dynamic image. Here it is a question of where you want to lose the information, if you want to sacrifice the clouds or the dark area under the bridge. I chose to meter for the sky and to keep everything in the upper part of the image visual. The brightest point of the sky was metered at 1/1000 at f6.3 and the darkest point under the bridge was metered at 1/8 at f6.3. All visual data is lost under the bridge. This means a dynamic range of 7 f-stops, which is clearly more than my camera can manage.
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Exercise 10: Colour cast and white balance
The images above were taken in full sunlight conditions. The different white balance settings makes the sky in particular look very different. The image with the shade white balance looks the worst, looking yellow, wheras the sun light white balance looks the best with saturated colours. The auto white balance is very close, only just a little bit less saturated.
The images above were taken in cloudy light conditions. It is difficult to see the difference in white balance on the rose because of its orange colour. It is easier to see on the background and the sky. The sky in the image with sunlight white balance looks too blue, as it was a grey and cloudy day. The shade white balance looks too yellow. It is more difficult to say if the image with the shade white balance or the auto white balance is the best, but the sky looks more grey in the one with shade white balance, so this one gets my vote this time.
The images above were taken in shady light conditions. I presumed that the shade white balance would look best here, but I think it looks too yellow. The best version is the auto white balance in my opinion. Maybe I didn't take this in the "right kind of shade"?
The images to the left were taken with mixed lighting: sunlight/tungsten. Natural light would give a blue light and the bulb gives a yellow light.
In the first image, using sunlight whitebalance, the evening sky appears pink and the lamp gives a cosy yellow shine. This is my favourite. In the second image, the tungsten white balance corrects the yellow shine from the lamp, but also makes the sky too blue. In the third image, the auto white balance corrects both the daylight and the tungsten light nicely. It looks quite natural. It is a question of personal preference and what you are trying to acheive. I like the first image the best, because it gives the inside a cosy feeling looking out on the calm evening sky. |
Assignment 2: Digital image qualities
All details about this assignment are in my report to my tutor.
All details about this assignment are in my report to my tutor.