Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
03-17-2010, 01:39 AM   #61
Veteran Member
GoremanX's Avatar

Join Date: Dec 2009
Location: Georgia, VT
Photos: Albums
Posts: 1,652
You didn't convert THAT one to sRGB (see? that setting just encourages mistakes)

I think the sharpness of that picture is just fine. I also think detail looks good, at least as far as I can tell at web resolutions. You realize of course that the *ist had pretty good image quality for a DSLR? It didn't improve by leaps and bounds in subsequent models, it was always just an incremental improvement.

If you really want to get an idea of what's going on as far as megapixels go, shoot in RAW and then compare the file sizes. As you've learned, comparing JPG sizes is very misleading and unpredictable, but RAW files tend to always fall within the same size range.

03-17-2010, 02:51 AM   #62
Veteran Member
justinr's Avatar

Join Date: Dec 2009
Location: Tipperary
Photos: Gallery
Posts: 394
Original Poster
These were taken before the great colour space debate started and I must admit that I hadn't realised that it had been settled.

Ok, First of all I'm sure that we all appreciate that jpegs are fairly elastic items and dependent upon subject complexity and light levels etc, but I still stand by my contention that a 10mp dslr should be producing significantly larger jpeg files than a 6million pixel dslr. If the compression ratio is similar (and why shouldn't they be?) then you would expect on average the smaller camera to create files 60% of the size of the 10mp camera. Or to put it the other way round I should be getting files approximately 1.67 times as large from the K10 than the ist. This is blatantly not happening, nor anyway near.

Just as a point of comparison my 22 million pixel Mamiya ZD is far more variable and kicks out jpegs of between 10 and 15mb, but I usually shoot to RAW on that anyway.

If Canon and Pentax used similar algorithms then my old 8mp Canon 30D should produce files 1.34 times as large as the ist, and lo and behold the average file size from it was around 3.5mb - 4mb, which is what I'd expect.

If the ist produces files of 2.5 to 3 mb then the K10 could be expected to create jpeg files of up to 5mb or 200 shots per 1gb card. Turning to my K10 manual it says that I can indeed expect to hold 200 shots on a 1GB card!

I have just taken some pictures of a similar scene out of the window with three cameras all set for max jpeg quality. All figures in MB's

K10
Pen RAW 13.3 Jpeg 3.48
DNG Raw 16.3 Jpeg 3.58
Jpeg alone 3.48

Ist.
Jpeg alone 3.48

Mamiya ZD
8.9*

K10 set to record at 6mp
2.45


Has anyone else a K10 that we could compare file sizes with?

* Which strikes me as being lower than normal, but the whole beast is a little unpredictable, hence the need for a reasonable dslr as well,
03-17-2010, 03:19 AM   #63
Veteran Member
GoremanX's Avatar

Join Date: Dec 2009
Location: Georgia, VT
Photos: Albums
Posts: 1,652
QuoteOriginally posted by justinr Quote
If the compression ratio is similar (and why shouldn't they be?)
See there's the error in your reasoning. There is no "ratio". JPG compression is way more complex than that. It has nothing to do with ratios or anything like that. JPG compression looks at your picture square-by-square (the size of the squares depends on which setting the camera manufacturer has chosen), discards the details which would normally be imperceptible under normal conditions, and then replaces that detail with whatever happens to be most prominent within that square. So the less detail in your picture, the smaller the file ends up being. The only thing the JPG compression level determines is:

a) how big the squares are

b) which details get wiped out

It's entirely possible that Pentax changed the JPG algorithm between the *ist and the K10D, resulting in more efficient file sizes. Again, check the RAW file size for a more accurate idea of what's going on. JPG file size is completely meaningless. It's even more meaningless across camera brands. You're looking for meaning where there is none.
03-17-2010, 04:31 AM   #64
Veteran Member
justinr's Avatar

Join Date: Dec 2009
Location: Tipperary
Photos: Gallery
Posts: 394
Original Poster
Yes yes we all know roughly how jpegs work but it is still a cold hard fact that the smaller the jpeg the the less information there is and since all displays, printers computers are capable of handling jpegs one assumes that there is a standard by which they are expanded again, and therefore a jpeg of 3mb will show the same detail irrespective of which camera they were taken on. Otherwise you are saying that a 3mb Pentax Jpeg somehow contains more information than a 3mb jpeg from anyone else, or indeed their previous models. How so? If I print from a 3mb K10 jpeg will I get more detail than from a 3mb ist jpeg?

Now as far as RAW is concerned I have always been brought up to believe that a RAW file is a fixed entity for each camera as it is with the Mamiya and the DNG files from the Pentax. If you are referring to Pentax RAW then that is a compressed file and will vary. It's not what I call a RAW file at all, but these things change with the wind. For what it's worth the Pentax RAW file for the ist is 10.8mb whilst for the K10 it is 13.3 for a similar scene.

I have written to Pentax asking for their views, I'll let you know the outcome.

03-17-2010, 04:47 AM   #65
Veteran Member
GoremanX's Avatar

Join Date: Dec 2009
Location: Georgia, VT
Photos: Albums
Posts: 1,652
QuoteOriginally posted by justinr Quote
Otherwise you are saying that a 3mb Pentax Jpeg somehow contains more information than a 3mb jpeg from anyone else, or indeed their previous models. How so? If I print from a 3mb K10 jpeg will I get more detail than from a 3mb ist jpeg?
Yes of course it could contain more information if it's compressed efficiently. If you really understood how JPG compression works, you'd realize this whole line of questions is pointless.

QuoteOriginally posted by justinr Quote
Now as far as RAW is concerned I have always been brought up to believe that a RAW file is a fixed entity for each camera as it is with the Mamiya and the DNG files from the Pentax. If you are referring to Pentax RAW then that is a compressed file and will vary. It's not what I call a RAW file at all, but these things change with the wind.
You are completely wrong. A RAW file is in fact a pixel-by-pixel recording and there is no lost data whatsoever. Pentax PEF files are losslessly compressed. There is no loss of data. Compression doesn't mean loss of detail. Otherwise, every zip file you download would be missing data. DNG files are uncompressed on the K10D, but compressed on the K-7. In your case, you can directly compare DNG file size and see a correlation. JPG files, on the other hand, use lossy compression. Stuff gets thrown out every time you save it.

I'm really not sure what bizarre conclusion you're trying to reach with all this. Do you think maybe someone swapped camera sensors on you? You're taking megapixels way too seriously.

Last edited by GoremanX; 03-17-2010 at 05:06 AM.
03-17-2010, 05:03 AM   #66
Veteran Member
sterretje's Avatar

Join Date: Dec 2008
Location: Roodepoort, South Africa
Photos: Gallery | Albums
Posts: 3,534
QuoteOriginally posted by GoremanX Quote
...JPG files, on the other hand, are losslessly compressed. Stuff gets thrown out every time you save it.
Please correct, it's lossy
03-17-2010, 05:06 AM   #67
Veteran Member
GoremanX's Avatar

Join Date: Dec 2009
Location: Georgia, VT
Photos: Albums
Posts: 1,652
QuoteOriginally posted by sterretje Quote
Please correct, it's lossy
ack! I haven't slept all night Fixing original post...
03-17-2010, 05:28 AM   #68
Veteran Member
justinr's Avatar

Join Date: Dec 2009
Location: Tipperary
Photos: Gallery
Posts: 394
Original Poster
Why am I questioning all this? Only because it is completely and utterly contrary to what I have been told, read and experienced over the years.

If Pentax RAW files are not losslessly compressed then why do they vary so much in size? If, as you say, they are a pixel by pixel record of the image falling upon the sensor then I'm curious to know why I have over 3mb difference in Pentax RAW file size from the same camera?

A camera needs to record three things from a sensor-

The pixels position
The filter layout
The intensity of light hitting the pixel.

I don't think there is anything else, but I fail to see where there is scope to condense this information without throwing some of it away. If it's possible then how is it done other than knocking out empty bits of code I suppose, but information showing nothing is still information.

03-17-2010, 05:40 AM   #69
Veteran Member
GoremanX's Avatar

Join Date: Dec 2009
Location: Georgia, VT
Photos: Albums
Posts: 1,652
QuoteOriginally posted by justinr Quote
If Pentax RAW files are not losslessly compressed then why do they vary so much in size? If, as you say, they are a pixel by pixel record of the image falling upon the sensor then I'm curious to know why I have over 3mb difference in Pentax RAW file size from the same camera?
Easy...

open up Notepad, type a bunch of A's in it like this:
aaaaaaaaaaaaaaaaaa

dozens of them. Save the file as "bunchofas.txt"

Now start a new file again, this time type a real sentence that includes about the same number of characters as the first file. Save that one as realsentence.txt

Zip up each file separately. The one with a bunch of A's will be significantly smaller than the one with real words. Why? Because of the repeating pattern, which makes it easier to store more data in the same amount of space.

That's why losslessly compressed files vary in space, because they combine repeating patterns into one block with information on where that repeating pattern resides within the file. It's actually way more complex than that, but this is a good starting point. From this, you get more and more advanced compression algorithms that do a better job of compressing data.
03-17-2010, 05:59 AM   #70
Veteran Member
justinr's Avatar

Join Date: Dec 2009
Location: Tipperary
Photos: Gallery
Posts: 394
Original Poster
As I said, information that says there is no information is still information!

It therefore follows that if the record of what one particualar pixel recieved (nothing, for instance) is amalgamated with the records of other pixels and cannot be seperated out afterwards, ie it is assumed to be the same, then definitive information has been lost.

I agree, it may not make a hoot of difference to the end result but to my mind it is still, strictly speaking, lossy compression.

Anyway, I'm off to the local Paddy's day parade now to give the K10 another go.
03-17-2010, 06:06 AM   #71
Veteran Member




Join Date: Jan 2009
Location: Budapest
Posts: 821
Justinr, just drop the jpge file size thing 'cause you clearly got it all wrong and don't seem to understand how it really works. Jpg file size doesn't mean and matter much, to begin with. Your K10D uses higher and/or better compression than you ist, that's all.

Damn Brit, you adobergb snob Adobergb is just a tiny bit wider than srgb, and it's mostly in the less usefull range. Use Prophoto or Wide gamut if you want a significantly wider color space... not that the end results will be significantly better than using srgb all the way, but do whatever floats your boat
03-17-2010, 06:14 AM   #72
Veteran Member
sterretje's Avatar

Join Date: Dec 2008
Location: Roodepoort, South Africa
Photos: Gallery | Albums
Posts: 3,534
RAW files are compressed without loss (so lossless) and nothing is thrown away.

I did a test with a K10D versus a K100D and 18-55mm AL-II lens at 18mm. The jpeg filesizes are very comparable (around 3 MB each).
03-17-2010, 06:17 AM   #73
Veteran Member
justinr's Avatar

Join Date: Dec 2009
Location: Tipperary
Photos: Gallery
Posts: 394
Original Poster
I've just had a reply from Pentax who tell me that on a three star setting the jpeg size will be about the same as the ist and I should shoot on the four star setting for a slightly larger file size. Unfortunately there is no four star setting!

Thank you Simico for telling me I'm stupid, I wasn't aware of this until now (although the wife drops the occasional hint) but it seems I may not be alone.
03-17-2010, 07:14 AM   #74
Senior Member
kari's Avatar

Join Date: Feb 2010
Photos: Albums
Posts: 149
QuoteOriginally posted by justinr Quote
I've just had a reply from Pentax who tell me that on a three star setting the jpeg size will be about the same as the ist and I should shoot on the four star setting for a slightly larger file size. Unfortunately there is no four star setting!

Thank you Simico for telling me I'm stupid, I wasn't aware of this until now (although the wife drops the occasional hint) but it seems I may not be alone.
If you're worried that it's shooting at 6MP instead of 10 look at the resolution, not the file size!
03-17-2010, 10:03 AM   #75
Veteran Member
justinr's Avatar

Join Date: Dec 2009
Location: Tipperary
Photos: Gallery
Posts: 394
Original Poster
Whatever the debate about jpeg size I'm a lot happier with todays results from the K10 having adjusted my techniques a little-



Still some soft focussed ones amongst the the files but I think this was because I didn't allow enough time for AF to work or too close etc.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
camera, dslr, jpegs, photography, sharpness, shots
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Can I use smc Pentax-A lenses on my *ist D/*ist DS? Ole Pentax DSLR and Camera Articles 3 05-18-2007 10:23 PM



All times are GMT -7. The time now is 11:35 PM. | See also: NikonForums.com, part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top