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01-27-2009, 03:17 PM   #16
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Thanks for that, interesting. Seems i'll stick to shooting 3200 RAW and pping in Neat Image.

01-27-2009, 04:32 PM   #17
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QuoteOriginally posted by UnknownVT Quote
I was skeptical about pushing ISO1600 -
since film pushed normally is not as good as film with the higher ISO rating.
Right, and I think that's true of ISO settings that are "real" on the camera - that is, if they are implemented by actually amplifying the signal from the sensor before analog-to-digital conversion. For ISO settings that are implemented by first doing to the a-d conversion and then simply doubling the values, there would be no difference whatsoever, assuming your software *also* performed it's push by simply doubling the values, rather than using some other algorithm.

GordonBGood as well as others looked at the actual numeric contents of the RAW files, and this left no doubt: ISO 3200 on the 6MP cameras contained only even numbers. Clearly, it was simply doubling the values after a-d conversion.

But ISO 800 is "real" - done by amplification of the signal - and as such, could presumably do better than pushing ISO 400.

Now, note that if you run the experiment in JPEG, then ISO 3200 *should* win over the ISO 1600 push, because the camera can perform the push on the original RAW data before it converts to JPEG, and hence has a lot more data to work with. It's hard to imagine how that could come out to be a disadvantage.

But for RAW, there *should* be no difference, unless your PP software chooses to do something other than simply double the values when you push exposure 1 stop. Depending on how clever the software is, what it does might turn out to be better than the simple doubling method used by the camera, or not. But in general, I certainly wouldn't expect it to do worse on average. Either it would be the same if it does just double the values, or slightly better if it knows of a better way (maybe something involving fractals, who knows).

The new K-m/K2000, BTW, apparently does have a "real" ISO 3200.

Anyhow, I say this not to invalidate your test your results, but to point out that whatever effect you are seeing might indeed still be, in effect, measurement error.
01-27-2009, 05:24 PM   #18
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QuoteOriginally posted by Marc Sabatella Quote
For ISO settings that are implemented by first doing to the a-d conversion and then simply doubling the values, there would be no difference whatsoever, assuming your software *also* performed it's push by simply doubling the values, rather than using some other algorithm.
How does one push by doubling the values on a JPG and RAW, please?

I merely used the brightness/contrast to try to match the ISO1600 1 stop underexposed to the straight ISO3200 -
so I was surprised to see the ISO1600 1 stop underexposed JPG adjusted looking better than the straight ISO3200 JPG.

Thanks
01-27-2009, 07:55 PM   #19
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QuoteOriginally posted by UnknownVT Quote
How does one push by doubling the values on a JPG and RAW, please?
I would assume that most PP software would simply double the values pre-conversion on a RAW image when moving the "exposure" slider one stop higher, but I can't swear any particular program did it. Presumably, any program would do that if that was indeed the optimal solution, but might try something else if it thought it could do better.

With JPEG, I suppose the same is true, but I wouldn't expect the results to be as good.

QuoteQuote:
I merely used the brightness/contrast to try to match the ISO1600 1 stop underexposed to the straight ISO3200
What program? Neither "brightness" nor "contrast" seem like logical names to me to accomplish an exposure push, but between the two of them, I guess it would be brightness. Contrast is definitely different. Isn't there also something labeled "exposure" or maybe "sensitivity"?

QuoteQuote:
so I was surprised to see the ISO1600 1 stop underexposed JPG adjusted looking better than the straight ISO3200 JPG.
Me too, which is why I'm assuming this was just kind of random variation (what I called "measurement error"). I think what it really suggests is that the differences are so small, they are dwarfed by normal variation. That is, even using the same exact settings and taking the same shot several times in a row, you would probably find differences at least as great as what you were seeing.

01-27-2009, 08:32 PM   #20
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QuoteOriginally posted by Scrapalina Quote
Still using K100D (NOT Super) and love doing so. BUT looking to upgrade. It doesn't need to happen immediately.

Is there was a "good time" to buy?

And what Pentax models to consider?

Thanks in advance.
The good time is was when Adorama had the K20D and lens for $700 (though I never recommend kit lenses.)
01-28-2009, 01:17 AM   #21
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QuoteOriginally posted by Marc Sabatella Quote
What program? Neither "brightness" nor "contrast" seem like logical names to me to accomplish an exposure push, but between the two of them, I guess it would be brightness. Contrast is definitely different. Isn't there also something labeled "exposure" or maybe "sensitivity"?
It's a lot more simple-minded on my part -
JPG - I am just using a photo editor and adjusting the Brightness and Contrast to try to get the ISO1600 1-stop underexposed shot to look as close as I could get it to the straight ISO3200.

RAW - I used Pentax Photo Lab 3 version 3.51 for the shots I posted previously - although I suspected the Sensitivity slider on the Other Settings Panel probably was incremented in stops (that version was not marked) -
I merely used it like a Brightness control.
For those previously posted RAW shots -
ISO3200 RAW - I used the adjustments on the Other Settings panel to get it the best looking I could.
ISO 1600 1-stop underexposed RAW - I used the adjustments on the Other Settings panel to try to get this shot to be as close visually as I could to the adjusted ISO3200 shot.
Then for both shots I used my photo editor to tweak the shots to get the best visually for me.

I have just now downloaded the latest version of Pentax Photo Lab 3 Version 3.61 - the Sensitivity slider is now marked as +1 etc - I am assuming stops.

So I re-did my RAW shots - using Lab 3 version 3.61 (under Custom Processing ie: NOT Full Auto Precessing)

ISO3200 straight - without any adjustments, ISO1600 only +1 on Sensitivity slider, no other adjustments -
100% crops (actual pixels) RAW -

these do look close but look kind of lack-luster - I definitely would do more post-processing of these images.

So I did some adjustments to "enhance" the images in my photo editor (actually only auto level and sharpen) which helps emphasize any differences -
100% crops (actual pixels) RAW after auto levels and sharpen -

I think the ISO3200 shot looks marginally just a fraction better than the ISO1600 1-stop underexposed Pushed shot... but there is very little in it.


QuoteOriginally posted by Marc Sabatella Quote
I would assume that most PP software would simply double the values pre-conversion on a RAW image when moving the "exposure" slider one stop higher, but I can't swear any particular program did it. Presumably, any program would do that if that was indeed the optimal solution, but might try something else if it thought it could do better..
With Pentax Photo Lab 3 - RGB values are shown at the mouse pointer position.

I picked a fixed point near the center of the image and read the RGB values -
ISO3200 RAW
No adjustments - R=151, G=148, B=117
ISO1600 1-stop underexposed RAW
No adjustments - R=105, G=93, B=64
+1 on sensitvity - R=150, G=138, B=107

hmmmm.. there are Odd numbers on the ISO3200 RGB values.
Also when the ISO1600 was increased by 1-stop on the sensitivity slider (therefore doubled?) - the RGB values also had Odd numbers.

Perhaps the RGB values are not the numeric values of the RAW file?

I think this does show on RAW ISO1600 1-stop underexposed and pushed 1-stop in Photo Lab 3 is about the same ISO3200 straight.

However I cannot figure out how to increase/push JPGs by 1-stop I can only make adjustements in my photo editor - the crudest is simple Brightness/contrast adjustments. But I can just use levels and "stretch" to get the "best" visually then add sharpen -
100% crop (actual pixels) JPG - Stretch/auto levels +sharpen

in these JPGs - the ISO1600 1-stop underexposed "Pushed" still looks a lot better.

Thanks for the conversation.

Last edited by UnknownVT; 01-28-2009 at 02:15 AM. Reason: info about editing
01-28-2009, 07:23 AM   #22
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Thanks everyone.

By no means do I need to upgrade as my K100 is a little gem.

However, my son asks me for my camera often and thought it may be time to upgrade and get a second body.

When is Photokina?

Since our camera is strictly for personal use. Would it make sense to find another 100d / 100dSuper / 200d?
01-28-2009, 07:53 AM   #23
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Good question. You could probably find a great deal on a NOS or a used K100DS right now. If the idea is to have two cameras so that your son can have is own I couldn't think of a better camera to get started with to learn photography. The only issue you should keep in mind is that when his birthday and Christmas come around you need to make sure you aren't buying him lenses for you to "borrow"

01-28-2009, 08:19 AM   #24
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Of course not!

Thanks.
01-28-2009, 11:46 AM   #25
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QuoteOriginally posted by UnknownVT Quote
It's a lot more simple-minded on my part -
JPG - I am just using a photo editor and adjusting the Brightness and Contrast to try to get the ISO1600 1-stop underexposed shot to look as close as I could get it to the straight ISO3200.
OK, but *which* photo editor? Maybe someone who uses the same program as you could suggest the best way to do it in that program. Shouldn't require the use of two different sliders, though - if you're using two sliders, you're doing something very different than what the Pentax firmware is doing when it pushes ISO 1600 to emulate 3200. But since you are doing your push post-conversion rather than on the RAW data, again, you can't possibly expect to do as well in simple push. If you're liking the results better, I think it's because you *are* going beyond a simple push and are also playi$gn with contrast.

QuoteQuote:
Then for both shots I used my photo editor to tweak the shots to get the best visually for me.
This could be a huge source of the sort measurement error I'm referring to. You want to take yourself out of the equation as much as possible. Move the sensitivity slider up to +1, and do nothing else. do this for about 5 different shots (and have 5 different shots at ISO 3200, too), then compare blind - *without* knowing which is which - to see if you can reliably out which re the 5 best and which are the 5 worst. If you really feel the need to do the test correctly.

QuoteQuote:
With Pentax Photo Lab 3 - RGB values are shown at the mouse pointer position.
...
hmmmm.. there are Odd numbers on the ISO3200 RGB values.
Yes, but RGB values are by definition post-conversion. When i said Gordon looked at the RAW values, I mean he looked at them *before* conversion to RGb. The conversion process involves applying WB info as well as downscaling from 12-bit (or whatever) to 8. So it's to be expected that you'll see the full range of the 256 values possible in JPEG. The question is, are you seeing the full range of 4096 values possible in RAW, and the answer was no - it was clearly just bit-shifted.

So measure all you want, but there's no getting around what the RAW files themselves prove- ISO 3200 is just a pushed ISO 1600. If you aren't getitng results as good, something is wrong with your methodology.

FWIW, I don't see any difference worth commenting on in your pics - it would be hard for me to imagine them being anything other than normal variation. Except in your last JPEG samples, in which it looks like the focus was slightly off on the ISO 3200 example. Which is also part of where normal variation comes from, and why I suggested running a number of tests if you're going to do it at all.
01-28-2009, 12:39 PM   #26
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QuoteOriginally posted by Marc Sabatella Quote
OK, but *which* photo editor?
FWIW, I don't see any difference worth commenting on in your pics - it would be hard for me to imagine them being anything other than normal variation. Except in your last JPEG samples, in which it looks like the focus was slightly off on the ISO 3200 example. Which is also part of where normal variation comes from, and why I suggested running a number of tests if you're going to do it at all.
Thank you for the explanation - my photo editor is PhotoImpact 8.

The first experiment was to just process the shots to get them to look the "best" visually to me -
ie: like I was just producing final photos -
I do very much realize that this is open to too many variations, so UNscientific -
but it does give me an idea of how well my photos could look potentially -
I really was just trying to find out if using ISO1600 1-stop underexposed would give me results that were as good as just shooting ISO3200 - in JPG.

I added the RAW as an afterthought - and I merely used Pentax Photo Lab 3 v3.51 like a photo editor to try to get the best visually looking image(s) I could - as it was, I ended up having to do a bit more tweaking in PhotoImpact 8 to get them as close as I could.

Once you explained what you were looking for - I re-did my processing to get a bit better control (second set) - especially for the RAW shots, as I now understood the sensitivity slider - so at least in RAW, I produced images that could be directly compared without complicating things. BUT I still did a minimal tweak/enhancement in PhotoImpact 8 as a separate set - just to get the results to look presentable to me - which I think actually helped emphasize the slight differences.

re: possible focus issues with ISO3200 JPG shot -
I have several ISO3200 JPG shots since I re-did my shots twice and did multiple shots at ISO3200 JPG - all my shots were tripod mounted, shake reduction Off, 2sec delay timer, central spot focus and focussed multiple times (to confirm) before shooting - all my other shots at ISO1600 and all the RAW shots (at ISO3200 and ISO1600) seem to show very good focus - all the ISO 3200 JPG seem to show a bit "soft" -
here are 4 separate shots at ISO3200 JPG taken at 2 different sessions - note there is an aperture difference 2 at f/4.5 and 2 at f/9.
All the shots were just cropped - auto-level and sharpened in PhotoImpact 8

100% crop (actual pixels) ISO3200 JPG -


there is a difference between f/4.5 shots (wide-open?) and the f/9 - but I think this shows there probably aren't any focus problems -
it's just soft because of being ISO3200 JPG.

Last edited by UnknownVT; 01-28-2009 at 01:01 PM.
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