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Old Feb 6, 2003, 1:03 PM   #1
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Default Picture File Size vs Application File Size

Iím curious. When opening a digital picture in an application such as Paint Shop Pro or Qimage it generally tells me the size of the picture. This application file size is always significantly larger than what my Window application shows. For example, Paint Shop Pro says one of my pictures is 793K while the property under Windows XP shows the file size at 112K.

Sometimes larger files can increase dramatically. A digital picture showing up under Window XP as 2.5 megs may be as large as 16 to 32 megs under an application which slows down the application. I made a mistake one time and accidentally resized one of these pictures to twice it size and crashed the system when the picture it was trying to resize got to 350 megs. Can someone explain this to a novice?
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Old Feb 6, 2003, 3:40 PM   #2
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The smaller file size is the file size on your disk. I assume you're working with JPEG files (.jpg). This file is compressed to take up less disk space. In order to manipulate the file, your photo program must uncompress the file and it is this larger uncompressed file size that you are seeing in the photo program.

Here's a tutorial that might be of some help:

http://www.shortcourses.com/editing/index.htm
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Old Feb 7, 2003, 12:09 AM   #3
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DUH! I should have known. Thanks for the help. Yes I was talking about JPEG files.

One quick question. How do I know how large a file will be in an application once its decompressed? For example, how could I tell that a 2.5 meg JPEG file will decompress into a 16 meg file in an application? While opening one or two pictures up does not affect the performance of my system opening 6 or 7 up does.

As advised here in many of the forums I have my 3.0 meg camera set at the large picture size. This gives me great pictures but BIG pictures.
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Old Feb 7, 2003, 9:21 AM   #4
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JPEG format has 8 bits per channel. Your file is most likely in RGB, it's 3 channels, 24 bits or 3 bytes for each pixel. If you use 3 megapixel camera you'll get 3M * 3 = 9 Megabytes. If you move to CMYK, 4 channels per pixel, image will become 12 Mb. Grayscale, 1 channel, will be 3Mb.
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Old Feb 9, 2003, 2:50 PM   #5
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I'm not sure about PSP or Qimage. Photoshop shows the uncompressed file size in the lower left hand corner of the window.
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Old Feb 9, 2003, 4:55 PM   #6
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Sergey..... You've left us a bit confused! I'ts not possible to calculate the uncompressed file size without knowing how much detail and how much JPEG compression is used in the camera.

A subtle point with many cams is the compression ratio does actually vary between modes and makes, making picture comparisons -like with like, more difficult. The calculation you gave was not for a JPEG image, but the image data before JPEG is applied!

I could heavily compress a pic. file to 1 Mbyte JPEG and it might come out 20M bytes opened in an editor - pic. quality won't be up to much though! you can try out all this, by saving a bitmap image as a JPEG at different compression ratios, look at the file sizes, then open them up in an editor and look at the quality. You can find out your cams compression ratio by looking at the manual or the EXIF data. But isn't it just as easy to shoot some typical pics and compare the file size on the card with the size when opened?

Harley...

Quote:
As advised here in many of the forums I have my 3.0 meg camera set at the large picture size. This gives me great pictures but BIG pictures.
You can never go back to shoot your pic again if you ever need that BIG print. PC memory is pretty cheap, so I'd up that and keep getting the best from your cam. The only reason you might want several pics open at once, is for batch work. Some editors offer the option to batch process by re-loading each file in the same window. If you're doing slideshows, keep the cam original files but consider making some downsampled copies to get the pc working faster.

The BIG pictures are down to how your monitor sees them, check out the size options in your editor and select 'fit to window', OK it's still consuming the same pc memory. Most editors will hold the same file size again in memory (so that's twice the uncompressed size) Anything less than 128Mb pc ram is a really a non-starter.
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Old Feb 10, 2003, 8:38 AM   #7
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Quote:
Originally Posted by voxmagna
Sergey..... You've left us a bit confused! I'ts not possible to calculate the uncompressed file size without knowing how much detail an2d how much JPEG compression is used in the camera.
Sorry for the confusion. The question was: "How do I know how large a file will be in an application once its decompressed?" and I answered this question.
Sergey

To make it more clear: it doesn't matter what compression was applied - the size of the image in application will be the same.
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Old Feb 10, 2003, 1:43 PM   #8
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Ok I understand where you're coming from:

Quote:
To make it more clear: it doesn't matter what compression was applied - the size of the image in application will be the same.
Depends what resolution setting was used to take the shot! Can't assume everybody is using max. So to apply your 'rithmetic you need to work the sums out on the image properties (image resolution data - not file properties).

What I assumed was that a Newbie sees a collection of compressed files on a card (taken at various cam settings), but hasn't opened anything in Photoshop and wants some idea what the uncompressed file size will be, so he knows in advance if the pc will crash out on resources!

I had this prob. with an older pc. and used a viewer (ACDSee or PicaView) first, set for thumbnail view only, to check image sizes. It can be the same problem when printing a JPEG file. You click on all the big print resolution numbers, feed in a highly compressed JPEG, but nothing tells you how much memory is needed to spool the print file, or how long it will take.

My advice still goes, if Harley is putting up with a poor pc, then capture at highest res. and downsample a copy to something the pc and printer can handle better if only printing up to 6X4. Then when the pc is upgraded, the high quality original pics are still archived.
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Old Feb 10, 2003, 3:00 PM   #9
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Thanks for the help. In Paint Shop the ratio is in the lower right hand corner. I forget where it shows up in Qimage and several other programs I have. They all differ a little.

My PC does fine if I have two or three files open but after that it sometimes can experience problems, especially if there are other applications open. What was surprising is that I sent a picture through email to several friends. Some email couldn't handle the traffic. Those who got it complained of the file size. I thought that I was sending a file of 500K when it really was over 2 megs. I shrink the pictures before sending now.
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