Megapixels – Are they important?

[Don Hoey]

treeve,

All sounds a bit odd to me. I suggest you post this and a pic in the Digital darkroom forum with details of your imaging program. People could then use that pic, and go through your routines and detail their results.

Don

[Don Hoey]

Originally Posted by miketoll

At what point does digital noise raise its head? For small sensors as found in compacts a lot of megapixels seems counter productive as the noise suppression algorithms needed seem to make the photos worse rather than better. The 6mp compact I use a lot of the time seems about the right compromise at the moment. SLRs with their bigger sensors will have a higher ceiling.

I agree. I think the mp race has gone a bit mad. I have just looked through DPR but have not found a test of a 10mp compact. I know they have commented on this subject though.

Don

[Don Hoey]

Originally Posted by Stephen Fox

50mm f1.8 was the lens of choice as resolution is high and could easily provide good results on both 4 and 12 Mpx cameras.

Totally understand the choice for this one Stephen. But I am sure lens quality will have an impact.

Perhaps I should have a go.

D2X plus Stevies £200 Sigma 28-200 compared to the D100 and 55 micro or 105 f2.5.

Don

[Adey Baker]

Originally Posted by treeve

Excellent article, a question I have wanted to ask ....
Something I note is that when stored in the camera,
a 9500Mp picture takes up 2.2 Mb. If I rotate the photo
it become 1.3mb; and if I alter the contrast, or something,
and save again, it becomes 800Kb. What is being lost,
if anything?

When you save as a 'JPEG' (jpg) file a certain amount of detail in the image is thrown-out, so to speak, to keep the file size small, but is then 're-invented' when you open up the image again.

Some of the finer detail gets lost and, though it may still look fine as a photo, what you've got is a sort of 'simpler' image so every time you alter anything you have to 'save' when you close the image down and by saving as a JPEG again you throw out detail from the 'simpler' image.

This is why the file size is now smaller - the simpler the image the more the system can throw out because it's easier to re-invent it back again (check the file-size for a jpg image containing a large area of one colour).

Doing it several times will just make the image worse and worse each time as more and more fine detail is lost so always save as an un-compressed file type such as 'TIFF' (tif)

[Don Hoey]

Originally Posted by treeve

and save again,

Adey is dead right and I missed this critical bit when I read the post. Depending on the program you are using you will have various levels of compression. This suggests that your program is using medium compression levels with each save. Try a pic where you perform all operations and only do a save at the end and compare final file size with one that has multiple saves. Also check if you can adjust the compression level in your ' save as '.

Paint Shop Pro 7 & 8 work like that. If ' save as ' is set at 10% compression then that setting is also applied to ' save '.

Don

[treeve]

Thank you very much for the advice Adey and Don ...
I had not noticed that part of the Paint Shop Pro 7 "save" system.
I keep all my digital jpeg pics as taken on camera, copied on to
two external drives and two DVD copies. Always have four originals
and then make adjustments on the PC and laptop to a secondary copy.
So nothing lost, as it were. A bit of tinkering under the bonnet of PSP.


Adey, you have raised another question for me, now.
My camera is set to record jpegs, which can produce 4.4Mb pics
on Fine setting, or 2.2 Mb on Normal. If I was to copy these across
from the XD card, and convert them to TIFFs is this feasible, or daft?
Is it better to save them on camera as TIFFs and what would the
equivalent file size be then? It doesn't matter for document copying,
what matters is to get as many reasonable frames on one card.
For other work, I have six XD 1Gb cards, so have plenty of space.
In a week away, I can easily take 1200 frames, to sift out the chaff
later ... better to grab that shot of a passing ship than to regret it
afterwards.

Best Wishes, Raymond

[Adey Baker]

You won't have any problems just opening and closing jpegs to look at, etc. The problem comes when you want to change them in any way, which then requires a 'save.' It's at this stage that saving them as tifs is most useful.

With the prices of memory cards so reasonable for 1Gb and above nowadays, the main reason to choose either jpg or tif or RAW (if your camera has it) is the speed at which your camera can write the file to the card.

many modern compact digicams just have jpg available which is fine for speed and for normal sized photos is not a great problem- saving a file just once as a jpg will not be too harmful

[Canis Vulpes]

Originally Posted by Don Hoey

Perhaps I should have a go.

D2X plus Stevies £200 Sigma 28-200 compared to the D100 and 55 micro or 105 f2.5.

Don

At all opportunities I tried to isolate the image sensor to provide valid results. Once different cameras are used with different lenses results become a little skewed. It would be interesting to see how a 6Mpx camera with a high resolution lens compared with a high count Megapixel camera with a mediocre lens performs. It is something I applied some though to but decided not to include in the article preferring to keep things equal between all test examples.

Looking at my fine detail test, it would have to be a poor lens on the D2X to be anything like my 6Mpx example with a decent lens at the right aperture.

[treeve]

Thanks Adey, I have had this camera under a year, still
not found all the features .... at least I have everything
saved as from camera. Best Wishes

[miketoll]

Originally Posted by Adey Baker

You won't have any problems just opening and closing jpegs to look at, etc. The problem comes when you want to change them in any way, which then requires a 'save.' It's at this stage that saving them as tiffs is most useful.........
many modern compact digicams just have jpg available which is fine for speed and for normal sized photos is not a great problem- saving a file just once as a jpg will not be too harmful

My compact is jpegs only so I always keep the original file and any alterations are done as a copy and saved in a lossless format (adobes own psd) so as to not lose anything. If I want to save space I could then convert back to jpeg which should result in no loss but still as a copy. The psd could then be deleted but I mainly just keep the psd and don't bother with the second conversion.