Resolution measurements - TZ30 (ZS20) - Many images

Started Apr 3, 2013 | Discussions
J C Brown
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Resolution measurements - TZ30 (ZS20) - Many images
Apr 3, 2013

Resolution vs. aperture plot for 100 ISO images recorded at 34 mm focal length from 1.1 metres

The following images show the arrangements used to assess the resolution of my TZ30 at short and long focal lengths using the test chart described in this post:

http://forums.dpreview.com/forums/post/50706153

LCD display for images recorded at 34 mm equivalent focal length

Test arrangement for images recorded at 480 mm equivalent focal length

View of LCD display for images recorded at 480 mm equivalent focal length

After adjusting the scale, image position and level to the desired accuracy and setting the white balance test images were recorded from a distance of 1.1 metres with a focal length of 34 mm, apertures from F/3.7 to F/8 and ISO values from 100 to 1600 and from a distance of 14.2 metres with a focal length of 480 mm and apertures from F/6.4 to F/8 at 100 ISO.

Central crops from all of these images are available here:

http://www.dpreview.com/galleries/6778033705/albums/tz30-zs20-colour-resolution-tests

Resolution at a short focal length

The following image was shot at a 35 mm equivalent focal length of 34 mm.

Image P1000147r

As illustrated in the above crop the resolution for each colour may be calculated by choosing the smallest E of each colour which can be easily recognised as an E, noting the value of its line thickness and dividing the height of the image in pixels by that value.

Thus for the TZ30 which has a sensor height of 3240 pixels, if the thickness of the lines in the smallest easily recognisable E is 1.4 pixels then the resolution will be 2314 LPH, (3240/1.4).

Resolution vs. Aperture

The results obtained from the seven shots taken at 100 ISO were entered in the above tables and used to create the following plots of resolution vs. aperture for the black Es and for black and the six colours.

As can be seen from these plots, for a focal length of 34 mm the maximum resolution for black and most of the six colours is about 2300 LPH from the maximum aperture of F/3.7 to an aperture of F/5 beyond which it declines steadily to about 1800 LPH at F/8 due to diffraction.

Resolution vs. ISO Value

To investigate the variation in resolution with ISO value the line thickness of the smallest recognisable E of each colour in the F/3.7 image recorded at each of the five ISO values was used as described above to prepare the above tables which were used to create the following plot which shows the variation of resolution with ISO for each colour.

As can be seen from the above plot, the variation of resolution with ISO value for the red, blue, black and magenta Es is very similar with the value dropping steeply from 2300 LPH to 2000 LPH then reducing gradually to about 1900 LPH. For the green Es the result is only slightly poorer but for the cyan and especially the yellow Es the result is very much poorer.

As may be seen from the above 1600 ISO image and from images P1000147, P1000154, P1000161, P1000168 & P1000175 in my TZ30(ZS20) Colour Resolution Tests Album, in addition to the reduction in resolution the increase in ISO value also results in increased spreading of the colour from the letters into the white area between them.

Resolution at maximum focal length

The following image was shot at a 35 mm equivalent focal length of 480 mm at 100 ISO

Central crop from image P1000286M showing the smallest easily recognisable Es

As illustrated in the above crop the resolution for each colour was assessed as described above and the results entered in the following tables. These show that the resolution at the maximum aperture of F/6.4 is about 2000 LPH and declines steadily to about 1800 LPH at F/8.

I hope that the information and test results provided in this post will be of some value to owners of TZ30 (ZS20) and similar cameras.

Jimmy

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J C Brown

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J C Brown
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Re: Resolution measurements - TZ30 (ZS20) - Badly distorted image
In reply to J C Brown, Apr 3, 2013

After I posted this thread I found that although the version of the original image in my gallery is correct the aspect ratio of the second image, which shows the test arrangement for the images recorded at 34 mm equivalent focal length, was very badly distorted.

Unfortunately my subsequent attempts to correct it were unsuccessful as was my attempt to post a replacement image. I have reported the problem via the feedback facility and am awaiting advice.

Please accept my apologies for any inconvenience.

Jimmy

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kkardster
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Re: Resolution measurements - TZ30 (ZS20) - Badly distorted image
In reply to J C Brown, Apr 3, 2013

That's OK - DPR's done that to me this week as well.  Thanks for the detailed work!

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Bruce
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J C Brown
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Re: Resolution measurements - TZ30 (ZS20) - Badly distorted image
In reply to kkardster, Apr 3, 2013

kkardster wrote:

That's OK - DPR's done that to me this week as well.  Thanks for the detailed work!

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Bruce
You learn something new every time you press the shutter

Thanks very much for the positive feedback Bruce. I'm pleased to hear that the fault is with DPR and not due to an error on my part.

Jimmy

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Jerry045
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Re: Resolution measurements - TZ30 (ZS20) - Many images
In reply to J C Brown, Apr 3, 2013

That is an awesome amount of work Jimmy. Very comprehensive and very well done. One can certainly see the well documented fall-off of resolution due to diffraction at smaller apertures and high ISO's.

Thanks for putting so much effort into that work. It was obviously a herculean effort.

Now that you have your TZ30 totally characterized, you need to go out and get us some scenes of the Scottish countryside with it. Those picture serial numbers are awful low!!

Thanks again,

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Erik Ohlson
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Re: Resolution measurements - TZ30 (ZS20) - Many images
In reply to J C Brown, Apr 3, 2013

Amazing job!

It makes me feel pretty good about my own conclusions reached much less rigorously - shoot wide, minimum of ƒ4.5.

Noting that one anomaly with the cyan, possibly ƒ4.5 could be considered the "Sweet Spot".

Thanks for this one!

-Erik

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sherman_levine
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Re: Resolution measurements - TZ30 (ZS20) - Many images
In reply to J C Brown, Apr 4, 2013

Jimmy,

That's quite a comprehensive effort, and very well presented.

I finally understood from ...147M that you select the smallest row with a _single_ clear E, which makes total sense from the design of the sensor and the table, but did not quite imbed itself into my head until now.

That's a very objective (and rational) approach.

Sherm

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kkardster
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Re: Resolution measurements - TZ30 (ZS20) - Many images
In reply to J C Brown, Apr 4, 2013

Regarding your yellow woes, perhaps part of the reason it measures poorly is its yellow-on-white color combination and the difficulty that that low contrast combination presents to the human eye.  Perhaps half of the yellow Es should be displayed against a background with better contrast to increase the chances of identifying its minimum clarity.  (Of course, having to print both the foreground and background rather than just the foreground can lead to bleeding or encroachment - depending on how good your printing process is.)

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J C Brown
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Re: Resolution measurements - TZ30 (ZS20) - Many images
In reply to Jerry045, Apr 4, 2013

Jerry045 wrote:

That is an awesome amount of work Jimmy. Very comprehensive and very well done. One can certainly see the well documented fall-off of resolution due to diffraction at smaller apertures and high ISO's.

Thanks for putting so much effort into that work. It was obviously a herculean effort.

Now that you have your TZ30 totally characterized, you need to go out and get us some scenes of the Scottish countryside with it. Those picture serial numbers are awful low!!

Thanks again,

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Jerry

Jerry

Thanks very much for your very complimentary remarks. It is great to hear that my efforts are appreciated and that I have been successful in presenting my findings clearly.

With regard to your comment about the serial numbers of my test images being awful low, I guess I need to get out more.

On a more serious note I suspect that is partly due to my having too many other interests and commitments and partly to many years of being limited to two or three 36 exposure cassettes of colour slide film during two week vacations in my pre-digital years. I guess that in my case old habits die hard.

Jimmy

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J C Brown
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Re: Resolution measurements - TZ30 (ZS20) - For Erik
In reply to Erik Ohlson, Apr 4, 2013

Erik Ohlson wrote:

Amazing job!

It makes me feel pretty good about my own conclusions reached much less rigorously - shoot wide, minimum of ƒ4.5.

Noting that one anomaly with the cyan, possibly ƒ4.5 could be considered the "Sweet Spot".

Thanks for this one!

-Erik

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Erik,

Thanks very much for your kind remarks. I’m pleased to hear that the results of my tests agree with your own findings and make you feel pretty good about them.

In relation to your observation about the anomaly with cyan, it can on occasions be rather difficult to decide which of two lines of Es contains the smallest E of a particular colour which can be fairly described as being clearly recognisable as an E. In view of that I would recommend that you don’t read too much into the occasional point which lies outwith the general trend.

With regard to the use of maximum apertures with small sensor cameras I think you might be interested in the discussions in relation to these old "sweet point" related posts which I submitted on October 29th 2009 in response to BobT’s thread, “Do you take advantage of camera settings?”

See: http://www.dpreview.com/forums/post/33532784

and on 1st November 2009 in response to R Adamczak’s thread, “No real 'sweet spot' on lens in small sensor cams?”  See: http://www.dpreview.com/forums/post/33562829

Jimmy

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Re: Resolution measurements - TZ30 (ZS20) - Many images
In reply to sherman_levine, Apr 4, 2013

sherman_levine wrote:

Jimmy,

That's quite a comprehensive effort, and very well presented.

I finally understood from ...147M that you select the smallest row with a _single_ clear E, which makes total sense from the design of the sensor and the table, but did not quite imbed itself into my head until now.

That's a very objective (and rational) approach.

Sherm

Sherm

Thanks for your very kind remarks. I am very pleased to hear that with the example of the Es which I have underlined in the …147M image you now understand fully the way in which I intended my test chart to be used to assess the resolution for each colour.

It is very satisfying to know that you now regard its use as a very objective (and rational) approach. I assume that as a result you will understand why I’ve been advocating its use as a means of obtaining quantitative rather than qualitative results.

Jimmy

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sherman_levine
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Re: Resolution measurements - TZ30 (ZS20) - Many images
In reply to J C Brown, Apr 4, 2013

J C Brown wrote:

sherman_levine wrote:

Jimmy,

That's quite a comprehensive effort, and very well presented.

I finally understood from ...147M that you select the smallest row with a _single_ clear E, which makes total sense from the design of the sensor and the table, but did not quite imbed itself into my head until now.

That's a very objective (and rational) approach.

Sherm

Sherm

Thanks for your very kind remarks. I am very pleased to hear that with the example of the Es which I have underlined in the …147M image you now understand fully the way in which I intended my test chart to be used to assess the resolution for each colour.

It is very satisfying to know that you now regard its use as a very objective (and rational) approach. I assume that as a result you will understand why I’ve been advocating its use as a means of obtaining quantitative rather than qualitative results.

Jimmy

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J C Brown

I regarded  it as such before....but now I better _understand_ the reasons for doing so

Sherm

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Re: Resolution measurements - TZ30 (ZS20) - For kkardster
In reply to kkardster, Apr 4, 2013

kkardster wrote:

Regarding your yellow woes, perhaps part of the reason it measures poorly is its yellow-on-white color combination and the difficulty that that low contrast combination presents to the human eye.  Perhaps half of the yellow Es should be displayed against a background with better contrast to increase the chances of identifying its minimum clarity.  (Of course, having to print both the foreground and background rather than just the foreground can lead to bleeding or encroachment - depending on how good your printing process is.)

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Bruce
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Bruce

Thanks for taking the time to consider the results of my tests and for passing on your thoughts about the much lower resolution values for the yellow Es and your suggestions in relation to increasing the contrast for these letters by using a grey background.

Having endeavoured to take a purely objective approach to such problems throughout my career I don’t regard these results for the yellow Es as “woes” but simply as limitations in need of a logical explanation.

Having been aware for several years of very similar behaviour in several different camera models I have given a good deal of thought to the various factors which could influence the lower values for the cyan and yellow Es.

In addition to the difficulty which you describe of the low contrast that the yellow on white combination presents to the human eye I have considered several other factors. These include the accuracy of the printed image which in addition the colour accuracy of all the letters including yellow also involves the whiteness of the paper on which the chart has been printed.

To achieve that with the highest possible accuracy when constructing the test chart I used combinations of the Zero and 255 settings for Red, Green and Blue in Photoshop Elements to set the three primary and the three secondary colours. As I don’t have access to professionally calibrated analytical instruments I have no means of measuring the accuracy of the printed colours and have had to rely on my own visual assessments.

The accuracy of the colours in the recorded image may also be affected by the properties of the light used to illuminate the chart, the accuracy with which the white balance has been set and the accuracy with which the grey level has been adjusted by means of the EV setting.

Assuming that as a result of the care taken with all of these factors and settings the image projected onto the sensor is reasonably accurate the accuracy of the recorded image may be affected very significantly by the properties of the sensor, the position of the individual Es in relation to the arrangement of the colour filters of the Bayer Matrix and the accuracy of the demozaicing software used to derive the recorded image.

As yellow is a 50:50 combination of red and green and cyan is a 50:50 combination of blue and green, the resolution with which the cyan and yellow letters is recorded is likely to be adversely affected by their positions in relation to the positions of the red, green and blue filters on the sensor.

In spite of these limitations I believe that although my new colour resolution test cannot provide absolute values it does provide a useful means of making quantitative rather than qualitative comparisons of cameras and camera lens combinations.

Thanks again for your interest and for your helpful comments.

Jimmy

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karlreed
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Re: Resolution measurements - TZ30 (ZS20) - In sights into how to test..
In reply to J C Brown, Apr 5, 2013

Sadly, I stopped teaching software testing almost five years ago;  if I was still teaching, I'd be using your approaches (and Ken Rockwell's) to get students thinking about how to test.

In this case, you have put a huge effort into getting resolution tests that are as useful as the best professional results, and, they involve techniques we can use ourselves with a little difficulty.

What's more your images relate to images we may actually capture, in that we can see the colours and the image size as it is.

Warm Regards, and, I may even get one of these cameras just for fun.

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J C Brown
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Re: Resolution measurements - TZ30 (ZS20) - In sights into how to test..
In reply to karlreed, Apr 5, 2013

karlreed wrote:

Sadly, I stopped teaching software testing almost five years ago;  if I was still teaching, I'd be using your approaches (and Ken Rockwell's) to get students thinking about how to test.

In this case, you have put a huge effort into getting resolution tests that are as useful as the best professional results, and, they involve techniques we can use ourselves with a little difficulty.

What's more your images relate to images we may actually capture, in that we can see the colours and the image size as it is.

Warm Regards, and, I may even get one of these cameras just for fun.

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karl reed

Karl

Thank you very much for your interest and for your very complimentary remarks.

I am delighted to hear that you think that I’ve succeeded in creating a resolution test chart which in addition to being relatively straightforward to use allows acceptably accurate measurement of the B&W and colour resolution of digital cameras.

If you are interested in knowing more about the development and use of the chart you may find the following posts of interest. See: “Dpreview's OM-D E-M5 Review, Second thread”

http://www.dpreview.com/forums/post/41382128

http://www.dpreview.com/forums/post/41438422 and

http://www.dpreview.com/forums/post/41487280

With regard to your suggestion that "I may even get one of these cameras just for fun" I think that you might be pleasantly surprised by the quality of the results which can be obtained with such a small easily pocket-able yet very versatile camera.

Regards

Jimmy

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karlreed
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Re: Resolution measurements - TZ30 (ZS20) - In sights into how to test..
In reply to J C Brown, Apr 5, 2013

Hi Jimmy,

Funds are always an issue, I have a D200, D700 and a Sony RX100.

If I manage to sell the D200, I'll possibly look at the TZ30.

REgards

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Jerry045
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Re: Resolution measurements - TZ30 (ZS20) - In sights into how to test..
In reply to karlreed, Apr 5, 2013

Karl:

Let me second Jimmy's comment that it is a fun camera. I just purchased a ZS19 which is the same camera as the TZ30 minus the GPS. I have been having a ball with it. I don't know if you get the same opportunities down under, but I got mine refurbished at 1/2 the going rate through Amazon. I could not pass it up at that price.

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Re: Resolution measurements - TZ30 (ZS20) - Refurbished models.
In reply to karlreed, Apr 5, 2013

karlreed wrote:

Hi Jimmy,

Funds are always an issue, I have a D200, D700 and a Sony RX100.

If I manage to sell the D200, I'll possibly look at the TZ30.

REgards

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karl reed

Hi Karl,

You might wish to consider a refurbished ZS19 which is a ZS20(TZ30) without the GPS. For more information and to see some sample images see this thread posted by Jerry045.

See: http://www.dpreview.com/forums/post/51035223

Regards

Jimmy

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Ianperegian
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Re: Resolution measurements - TZ30 (ZS20) - For kkardster
In reply to J C Brown, Apr 8, 2013

Hi Jimmy,

Thanks for a very interesting thread, and thanks also for making your resolution charts freely available for people to use for their own testing.  i think your charts are very ingenious, and they provide a much more reliable way of visually assessing resolution than do the B&W "narrowing lines" charts that are often used on the review sites, as well as allowing different colours to be assessed at the same time.

I noticed kkardster's comment about the lower resolution of the yellow Es.  I wondered whether changing the background colour would have any effect, since I understand that in the demosaicing of a Bayer matrix the colour value of a pixel includes interpolation from the surrounding pixels.

I thought to try blue as the background since as you said, yellow is made up of red and green, and pure blue lacks both red and green.  I prepared a copy of your earlier Es chart with a blue background using PSE with the paint bucket tool (obviously the blue Es disappear).  Printing this chart at the correct size (75mm for the black line) with my Epson printer gave good resolution of the smallest Es, as shown in a closeup shot I took with my ZS20:

I attached the blue background chart print onto the chart board I'd previously prepared for testing my FZ38 and ZS20, as shown here .

I tested using my ZS20 at 51mm FL with the tripod adjusted to the correct distance so that the black line on the chart covered 400 pixels. Below is the resulting full sized image:

This is a 100% crop of the blue background chart beside the white background chart:

As can be seen, the blue background has had a marked influence on the Es, with the yellow Es being much better resolved, while black Es (and text) are poorly resolved.  It seems to indicate that yellow, cyan and probably other colours too, give better resolution when they are surrounded by particular other colours.  Also, I think the intensity of the background colour and the exposure would have some effect as well.

A conclusion could be that when taking shots of canaries, choose a blue sky background rather than a white clouds background!

Ian

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Re: Resolution measurements - TZ30 (ZS20) - For Ianperegian
In reply to Ianperegian, Apr 9, 2013

Ianperegian wrote:

Hi Jimmy,

Thanks for a very interesting thread, and thanks also for making your resolution charts freely available for people to use for their own testing.  i think your charts are very ingenious, and they provide a much more reliable way of visually assessing resolution than do the B&W "narrowing lines" charts that are often used on the review sites, as well as allowing different colours to be assessed at the same time.

I noticed kkardster's comment about the lower resolution of the yellow Es.  I wondered whether changing the background colour would have any effect, since I understand that in the demosaicing of a Bayer matrix the colour value of a pixel includes interpolation from the surrounding pixels.

I thought to try blue as the background since as you said, yellow is made up of red and green, and pure blue lacks both red and green.  I prepared a copy of your earlier Es chart with a blue background using PSE with the paint bucket tool (obviously the blue Es disappear).  Printing this chart at the correct size (75mm for the black line) with my Epson printer gave good resolution of the smallest Es, as shown in a closeup shot I took with my ZS20:

I attached the blue background chart print onto the chart board I'd previously prepared for testing my FZ38 and ZS20, as shown here .

I tested using my ZS20 at 51mm FL with the tripod adjusted to the correct distance so that the black line on the chart covered 400 pixels. Below is the resulting full sized image:

This is a 100% crop of the blue background chart beside the white background chart:

As can be seen, the blue background has had a marked influence on the Es, with the yellow Es being much better resolved, while black Es (and text) are poorly resolved.  It seems to indicate that yellow, cyan and probably other colours too, give better resolution when they are surrounded by particular other colours.  Also, I think the intensity of the background colour and the exposure would have some effect as well.

A conclusion could be that when taking shots of canaries, choose a blue sky background rather than a white clouds background!

Ian

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Hi Ian,

Thank you for your very kind remarks about my test charts and the reliability of measurements derived from them. Thanks also for the time and trouble you’ve taken to investigate kkardster’s suggestion about the low contrast of yellow on white by changing the background colour to blue prior to printing.

The central crop from the image of your full test chart demonstrates clearly that the colour of the background has a significant effect on the resolution of Es of different colours.

To illustrate the effect more clearly I’ve taken small crops from the area around the 1.5 pixel Es on both white and blue backgrounds, pasted them side by side into a single image and used the Print Screen option to make the individual pixels clearly visible in the following image.

Comparison of appearance and resolution of coloured Es printed on white and blue background

As may be seen from the composite image above the appearance of the green, cyan and yellow Es on the blue background is very similar to that of the red, blue, black and magenta Es on the white background. In addition the line thickness of the smallest recognisable Es of each colour is about 1.5 pixels which is consistent with the 1.5 pixel value derived from the graphical simulation described in my report on the resolution of the FZ50.

Your conclusions about the influence of background colour on the resolution of Es of different colours are also consistent with my experience of using bracketed exposures while trying to find the optimum exposure during some of my earlier tests.

These tests revealed that the difference in the shades of grey which resulted from a +/- 0.33 EV difference in exposure was sufficient to make a noticeable difference to the ability to clearly recognise Es of different colours and that for assessing resolution a light grey background was preferable to a white one.

Thanks again for your interest and for your interesting contribution.

Jimmy

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