Resolution and Compression on digital cameras

  Carafaraday 14:29 03 Aug 2003

I have a Canon A70 and am trying to get to grips with the whole process of digital photography. Could someone kindly explain the difference between Resolution and Compression, and what difference is made by altering one or the other (or both).

  DieSse 15:32 03 Aug 2003

Resolution refers to the number of pixels - dots - in the image. Note that this is independant of the viewed size of the image. The sensor in the camera will have a maximum number of pixels it can handle.

If you reduce the number os pixels in the picture you take, there are literally less dots. This makes a difference as you increase the viewing size, as the number of pixels stay the same, they will get larger. Remeber that the average computer screen, at say 800x600 pixels = 480,000 pxels in total - at 1280x1024 resolution it has 1.3m pixels.

Compression is an algorithm applied to the storage of the data in the picture, to reduce the size of the file. The more compression, the smaller the file. Compression actually lose information from the picture, so the more compression, the more information is lost. But NOTE, it does not change the nuber of pixels in the image.

  anchor 18:04 03 Aug 2003

My recommendation for the best results, (and giving a reasonable capacity on your media card), would be to use "large" for your image size, (2048 x 1536 pixels), and "fine" compression.

If you really need to squeeze more images on your card, then drop the image size to "medium 1", (1600 x 1200 Pixels), keeping compression on "fine". If you are absolutely desperate to get even more images on your card, then change compression to "normal".

  GPC 18:11 03 Aug 2003

Sending pictures via Email.
My pictures are typically as large as 700 or more megabytes and they take too long to upload or download.
They are in jpg format. Is there any software or procedure that I can use to minimise these file sizes?

  DieSse 18:46 03 Aug 2003

You should start your own thread, in order to get notified of replies, and save the originator of this thread getting notified of answers to you.

The problem is your pictures are too large in terms of numbers of pixels - try resixing them in a photo- package to a size of approx 00 pixels wide.

JPEG file are alraedy compressed - you could alter the jpeg settings for more compression, but this will degrade the picture quality - yu can experiment with how much extra compression, and what effect it has on quality and file size to reach what you consider is the best compromise.

But the resizing is the correct and best answer.

  Carafaraday 19:02 03 Aug 2003

Thanks for your detailed reply.
Would it be possible to print out an A4 sized pic from Med 1 + normal, or would that only be ok for say a 3 x 5 inch pic? I am presuming that you have a similar camera - if so, I'd really welcome any advice as to settings etc -= the whole world of digital photography is very new to me.

  GroupFC 21:05 03 Aug 2003

I have the A70 (as "anchor" will testify), but I too, am relatively new to digital photography.

This just to say that when I find the time I intend conducting an experiment by taking a picture of the same subject at all resolutions and compressions so that i can see for myself what the difference is!

So far I have only used medium 1 "fine" (1600 x 1200), and medium 2 "fine" (1024 x768). I have to say that I was a little disappointed with the medium 2 results, but that may be due to my general photography skills!

As yet I haven't printed any photos other than a few test shots, but I would have thought that if you are going to print at A4, you will need the highest resolution, but as anchor said this is of course a trade with the card capacity.

  Carafaraday 22:41 03 Aug 2003

Let me know when you have the results of your experiment - in the meantime I'll go for the best possible with the idea that I can always reduce the size of the file if I want to send by email or whatever.

Any other comments from other Canon A70 users welcomed.

  anchor 14:27 04 Aug 2003

Hello Carafaraday: Welcome to the world of Digital photography.

If you want to get a "good" A4, then follow my recommendations to use "large" image size, and "fine" compression.

The example you quote of Medium 1 and normal, would be adequate for a 5 x 3 inch. Remember, one the advantages of digital photography is the ability to crop unwanted parts of the picture. To do this, you would need a better quality original.

Compact Flash cards are quite cheap at the present; (64Mb £12.35, and 128Mb £17.55 + 95p postage from here);
click here),
so why not get the best results you can with extra cards. By the way, they also sell high power rechargeable NiMh batteries at a good price.

I now have the Canon S50, but have been a keen digital photographer, (with various cameras), for about 4 years.

  hssutton 15:00 04 Aug 2003

Pixels are expensive and memory is cheap. Don't compromise your picture quality, get the best that your camera can give, buy extra memory and follow "anchors" advice,

  961 17:38 04 Aug 2003

hs sutton is right. Your camera will take large size compactflash cards and they are not expensive.

If you are going to take a picture with this camera which has a super lens and will take terrific quality pictures, then why use anything other than the highest quality that the camera will produce, i.e. Large and superfine. This will produce top quality A4 pictures, even if cropped, always assuming you use a good photo printer and good photo paper.

To send pictures by e-mail you need to reduce the size of the file to about 120Kb, which can be done by many photoeditors such as Photosuite

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