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Author Topic: Exported image files much bigger than expected.  (Read 2747 times)
The View
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« on: June 07, 2007, 03:09:26 AM »
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I just exported nine images to a CD.

Original size RAW was 6 megapixels, converted to DNG at import. Adjustments.

But the nine images took 300 megabyte disc space.

Why did the images get so "fat"? I thought the adjustments in Lightroom were only stored as commands, not as whole pictures?
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Henry Goh
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« Reply #1 on: June 07, 2007, 03:12:43 AM »
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I just exported nine images to a CD.

Original size RAW was 6 megapixels, converted to DNG at import. Adjustments.

But the nine images took 300 megabyte disc space.

Why did the images get so "fat"? I thought the adjustments in Lightroom were only stored as commands, not as whole pictures?
[a href=\"index.php?act=findpost&pid=121545\"][{POST_SNAPBACK}][/a]

Did you happen to see what was the resolution you exported at?  On export you should see a screen for where the file is to be exported etc.  Somewhere at the lower section you should be able to see the resolution.

Henry

BTW you said you exported so that means LR should write out the full file to CD not just tags...
« Last Edit: June 07, 2007, 03:15:16 AM by Henry Goh » Logged
61Dynamic
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« Reply #2 on: June 07, 2007, 11:13:53 AM »
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300MB is what you should expect for 9 images exported as uncompressed 16bpc tiffs (or psd).

Why the increase in file size? There are three things.

1) A raw file is only a third of a final image. Due to the color filtering on camera sensors, the total amount of raw data is only the equivalent of a single channel. The rest of the data needs to be interpolated (an educated guess) to fill in the gaps for each red green and blue channel.

2) The kind of compression used has an effect.

3) The raw data is either 12bpc or 14bpc, usually 12 if it's a 35mm SLR. Tiffs and PSDs can only be either 8bpc or 16bpc so that 12/14bpc data gets placed in that 16bpc file and the gaps in the data are filled. Each pixel in each channel goes from having 12 bits describing it to 16. The final result is a file with more ones and zeroes describing your data and thus a larger file size.


If you want to reduce the hard drive space used there are a couple things you can do but they come at a cost. The first is to export at 8bpc but then you loose data and flexibility in editing. The second thing is to use compressed tiffs. this will nock your files from around 36mb each to just over 20mb each. However, there is a noticeable performance loss when saving and opening.
« Last Edit: June 07, 2007, 11:16:50 AM by 61Dynamic » Logged
The View
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« Reply #3 on: June 08, 2007, 06:28:05 PM »
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Thanks for the replies.

61Dynamic, this was very informative.

I just wanted to know what happened (if I didn't do anything wrong, like with those old word processors, whose files grew bigger and bigger with every correction you made).

Now I know that everything is OK. Thanks.
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The View
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« Reply #4 on: June 08, 2007, 06:30:45 PM »
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Actually, regarding STORAGE, what storage do you recommend?

At this time I have an iMac g5 2.1Ghz 20", but I will upgrade withing the next six to eight months.

So I don't want to buy expensive storage now, just basic for back-up.

What do you think of this drive for back-up?

It's a Seagate 250gb with 5 years warranty.

http://www.newegg.com/Product/Product.aspx...6822148233#spec
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61Dynamic
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« Reply #5 on: June 08, 2007, 06:45:31 PM »
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That'll do the trick for basic backups. You might want to consider a firewire drive though. They do perform noticeably faster (everything else being equal) and don't cost much more.

Also check out SuperDuper. It's a braid-dead simple backup utility.
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The View
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« Reply #6 on: June 08, 2007, 11:53:06 PM »
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Thanks for the software recommendation.

I guess I'm going to get a fire-wire drive.
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The View
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« Reply #7 on: June 17, 2007, 06:45:21 PM »
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I actually found out why the files were so large.

They were because I converted them to PSD for a client who wanted it in that format.

When I - after my back-up hard drive crashed - backed up images to CD and DVD, I saw, that 6MB RAW images with all the corrections were just 5MB large (e.g. 130 images had 650 mb).

I don't know why they are now smaller, but maybe that has to do that I converted them to DNG.

In PSD every alteration seems to significantly enlarge a file, while in a DNG file there are just changed instructions for a software on how to display the image, which do not increase file size.

Why 130 6MB DNGs only have 650MB - no idea. Maybe DNG is more efficient than the native (Pentax) RAW format.
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61Dynamic
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« Reply #8 on: June 19, 2007, 08:16:07 PM »
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Maybe DNG is more efficient than the native (Pentax) RAW format.
[a href=\"index.php?act=findpost&pid=123392\"][{POST_SNAPBACK}][/a]
You'd be right. Sometimes the compression used in DNG is noticeably more efficient than the manufacturer's.
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