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Bitmap File Size for 1024x768 Screen Resolution

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Nhmiller

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May 1, 2002, 3:20:55 PM5/1/02
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Would the file size I should scale down to be 1024 X 768 = 786,432? Or am I
supposed to multiply that by 3 for 24 bit color, so = 2,359,296? I have large
bitmap files which are scans of paintings, some as high as 100 megs, created to
make prints of the paintings. I want to display these on my screen as quickly
as possible but with the highest quality 1024x768 will allow. Then to have a
compressed file for a web site suitable for viewing at 1024x768 would I simply
save the 786KB (or 2.26 meg) file as a jpg?

If you are sending a Reply, please also choose the option (if you have it) to
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Neil Miller

Nhmiller

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May 1, 2002, 3:24:59 PM5/1/02
to
Would the file size I should scale down to be 1024 X 768 = 786,432? Or am I
supposed to multiply that by 3 for 24 bit color, so = 2,359,296? I have large
bitmap files which are scans of paintings, some as high as 100 megs, created to
make prints of the paintings. I want to display these on my screen as quickly
as possible but with the highest quality 1024x768 will allow. Then to have a
compressed file for a web site suitable for viewing at 1024x768 would I simply
save the 786KB (or 2.36 meg) file as a jpg?

Wayne Fulton

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May 1, 2002, 5:23:17 PM5/1/02
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In article <20020501152459...@mb-fd.aol.com>, nhmi...@aol.com
says...


Some BMP are 8 bit color and are compressed with RLE encoding.

Other BMP are 24 bit color and are not compressed. If 24 bits, and if 1024x768
pixels, the BMP file size will be near 1024 x 768 x 3 bytes, which is about
2.3 MB. If they are 10 MB, they are much larger than 1024x768 pixels. You
could resample a copy of them to 1024x768 pixel size if that is the goal.

Yes, you can also save a copy as JPG. Depending on JPG Quality factor, that
file might be 1/8 or 1/10 size then, but not maximum quality.

Even at 230KB, that's a pretty large and slow image for a web page (about a
minute each for many modems), and many web site visitors have screens smaller
than 1024x768 pixels. Around 600x400 pixels seems more reasonable.

--
Wayne
ful...@scantips.com
http://www.scantips.com "A few scanning tips"

Mac McDougald

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May 1, 2002, 5:30:30 PM5/1/02
to
In article <20020501152055...@mb-fd.aol.com>,
nhmi...@aol.com says...

> Would the file size I should scale down to be 1024 X 768 = 786,432? Or am I
> supposed to multiply that by 3 for 24 bit color, so = 2,359,296? I have large
> bitmap files which are scans of paintings, some as high as 100 megs, created to
> make prints of the paintings. I want to display these on my screen as quickly
> as possible but with the highest quality 1024x768 will allow. Then to have a
> compressed file for a web site suitable for viewing at 1024x768 would I simply
> save the 786KB (or 2.26 meg) file as a jpg?

All you had to do was save a file and then look at size, rather than do
the math, you know :-)

Here's what I wrote you in the other scanning group:

1024x768 24bit BMP file is about 2.3MB
Saving same as JPEG, using 75% quality in PhotoShop (toward best end) is
387KB
At 50% quality, 160KB


--
Mac McDougald
Doogle Digital - www.doogle.com

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