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Old Feb 11, 2003, 11:42 AM   #1
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Default Picture size v. file size

I am still mystified about the relative importance of picture size and file size.

I know of course that smaller files can't hold as much detail as big files, & this is demonstrated quite dramatically when you have a good picture in, say, a 750kb file and you try saving it in a 20kb file.

BUT when I look at the settings available on - e.g. the Olympus C2100UZ - I get puzzled. Two examples will illustrate. On the one hand I can set the camera so that it takes pictures 1600x1200 and records them in JPEG files that are about 500kb each. On the other hand I can set the camera so that it takes smaller pictures - e.g. 1280x960 - but that are recorded in JPEG files that are about 950kb - i.e. 50% bigger.

So - which of these two contains the more detail?
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Old Feb 11, 2003, 12:18 PM   #2
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Four things can affect file size:

1, Format e.g. TIFF or Jpeg etc.

2, The amount of detail in the picture (same picture, different light = different file sizes).

3, No (or # for you Americans) of pixels

4, Amount of compression (really only applies to Jpegs).

If I compress a 3mp picture enough I can reduce the file size to such an extent that the file size is smaller than a 2mp picture.

My camera (Oly 730) gives me a choice of compression settings (not SHQ) but in SQ1 I can choose Normal or High

Thats 90 pics in High and 255 in Normal for this memory card.

Therefore High is compressing much less than normal.

Hope this helps.

Get back to us if not and I'll try again.
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Old Feb 11, 2003, 12:41 PM   #3
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Default Re: Picture size v. file size

Quote:
Originally Posted by Herb
I am still mystified about the relative importance of picture size and file size.

I know of course that smaller files can't hold as much detail as big files, & this is demonstrated quite dramatically when you have a good picture in, say, a 750kb file and you try saving it in a 20kb file.

BUT when I look at the settings available on - e.g. the Olympus C2100UZ - I get puzzled. Two examples will illustrate. On the one hand I can set the camera so that it takes pictures 1600x1200 and records them in JPEG files that are about 500kb each. On the other hand I can set the camera so that it takes smaller pictures - e.g. 1280x960 - but that are recorded in JPEG files that are about 950kb - i.e. 50% bigger.

So - which of these two contains the more detail?
I would guess that the higher resolution (1600x1200) would yield the better detail, but it's also possible that the extra detail would be offset by the reduction in overall picture quality that results from heavy image compression.

Compression is used to increase the amount of data that can be stored on your camera's memory card. However, storing pictures as compressed JPG files, is something of a trade-off. JPEG is what's known as a 'lossy' compression scheme, meaning that some of the original information that you stored is corrupted (or lost) during the compression process. The heavier compression you use, the more pronounced this loss becomes.

Of course the ideal situation would be to store the image without compressing it, and for those photographers that insist on the absolute best results possible many higher-end cameras have settings to allow the image to be stored in an uncompressed state,
but most consumers aren't happy with storing just one or two images on thier expensive memory cards.

I hope that helps!
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Old Feb 11, 2003, 2:00 PM   #4
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Default Stilll puzzled

Yes, I understand that all sorts of factors like compression, and how detailed the subject matter is, and how bright, affect picture quality.

Perhaps I should have put my question differently. Suppose I have my camera on a tripod and take two JPEG pictures of a subject that's full of detail.

The first picture's taken at the 1600x1200 setting and 'HQ' - which gives a file of nearly 500kb. The second picture's taken at the 1280x960 setting and what Olympus call 'SQ - High Quality' which gives me a file of nearly 900kb.

In other words, when everything else is equal, what differences are there between the two JPEG pictures? Or is the answer - "It depends on other factors such as the subject matter"? And if it does depend on other factors, what are they and how do they operate?
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Old Feb 11, 2003, 2:00 PM   #5
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Another factor affecting JPG file size not previously mentioned is the subject of the picture. Photos with a lot of detail (leaves on a bush, feathers on a bird) are, everything else being equal will be much larger than one with less data, like sky or landscapes.
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Old Feb 11, 2003, 3:34 PM   #6
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What we are all missing, is that in all the different resolution modes (that's number of pixels in the image) a cam offers, the manufacturer is also attaching an arbitary quality setting: SHQ, Fine Medium etc. - and what does this mean?

They are pre-setting the variable amount of compression the cam applies as different factors in each mode, before saving the file as a JPEG. This compression factor is often shown in the EXIF data. Picture quality and stored file size are not easily related any more.

A lower resolution picture with less compression applied may well give a larger file size than a higher resolution picture with more compression. For one thing, lower resolution will not take high compression. On top of this the scene detail also affects stored file size. A 3Mpix cam can produces an approx 24Mbit uncompressed image, so there's plenty of range in the compression factor to end up with a 1 or 2 Mbyte stored image.

This is all trickery and you're bound to ask which is better? It's sad that you might be paying for more Mpix, but higher JPEG compression is applied because the image can take more, so you don't moan at the large file sizes, and fewer pics on the card!

Your choice becomes quality limited by resolution (an even loss of detail) or quality limted by JPEG artefacts or usually a mixture of both! However, the higher the captured Mpix, the more compression can be applied to get a similar pic. When might you choose lower resolution image less compression? There might be some gain in those scenes with large plain areas of sky or colour where a slight softness might be compromised for smooth colour transitions - but this is a real guess.

This is the dilemma when choosing High MPIX medium or lower MPIX high quality, and get similar file sizes. With cheaper memory the lower quality options become redundant and you should aim to shoot highest quality for the media size you can afford.

As bigger memory comes, I see cams where users determine the compression factor. But the lesson here is when you compare all those cam pics from XMpix cams, how often do you ask what compression ratio is the cam using, and are both scenes shot with different cams the same and stressing for compression? I think Oly's publish their compression factors for each mode but many others hide it in loose description like SHQ, HQ - and hope you won't look further in your comparison! There are some 2Mpix cams which will give pics as good or better than 3Mpix cams.
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Old Feb 11, 2003, 3:41 PM   #7
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The 1600 x 1200 HQ pictures does. You can resize it to 1280x960 and you either won't be able to tell the difference in the two, or it will be sharper. I, too, am puzzled as to why the lower res pics are stored in such an inefficient manner. The bottom line? Take EVERYTHING in HQ or SHQ mode; if you later want to resize it, you can. Besides, you can CROP the 1600x1200 much more than you can the 1280x960. You lose that flexibility if you take smaller formats.
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Old Feb 11, 2003, 3:48 PM   #8
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lg.. I think we posted the same time!

Quote:
I, too, am puzzled as to why the lower res pics are stored in such an inefficient manner
See my earlier post, I'm not looking for efficiency, but higher quality gain and that means more pixels less JPEG compression, higher file sizes, until better compression comes along.
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Old Feb 12, 2003, 12:16 PM   #9
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Default Re: Stilll puzzled

Quote:
Originally Posted by Herb
Yes, I understand that all sorts of factors like compression, and how detailed the subject matter is, and how bright, affect picture quality.

Perhaps I should have put my question differently. Suppose I have my camera on a tripod and take two JPEG pictures of a subject that's full of detail.

The first picture's taken at the 1600x1200 setting and 'HQ' - which gives a file of nearly 500kb. The second picture's taken at the 1280x960 setting and what Olympus call 'SQ - High Quality' which gives me a file of nearly 900kb.

In other words, when everything else is equal, what differences are there between the two JPEG pictures? Or is the answer - "It depends on other factors such as the subject matter"? And if it does depend on other factors, what are they and how do they operate?
You should already know this; but the on the Olympus cameras, the 'Quality Modes' are settings for different levels of compression.

As I've stated, the higher resolution image (the 1600x1200) should have the greater detail (since the image is recorded with a greater number of pixels) but you may also find the level of artifacting caused by the heavier compression to be unacceptable. This is really a matter of personal choice. (And it also depends somewhat on the intended size of your final output)

I would suggest that you do a test, exactly as you've explained above (shooting the same scene from a tripod, in each mode) and compare the outcomes yourself to decide which mode is preferable.
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Old Feb 12, 2003, 1:40 PM   #10
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Default Two different settings

I've just followed Crispy's suggestion & taken some pairs of pictures.

One of each pair was taken by my Olympus C2100UZ set at HQ (which produces pictures 1600x1200 in files of about 440kb).

The other one of each pair was taken at the best SQ setting (the one that produces pictures 1280x960 in files of about 800kb).

I then -

1. Made TIFF files from these

2. Applied the same amount of sharpening to each (because I always use my camera at the 'soft' setting, having read that my comouter programs do it better than in-camera sharpening).

3. Re-sized the HQ pictures down to 1280x960 so that I could compare the result to the identically-sized pictures taken in SQ.

The results are very interesting. I can see no difference in detail or sharpness, but the colour in the SQ pictures is slightly better.
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