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Gif's, dpi and stuff...
Do gif's have to be 72dpi?
CromeYellow




msg:850137
 4:37 am on May 21, 2002 (gmt 0)

Hi there

I'm currently compiling an ebook which is comprised mainly of black and white images.

There are quite a few of them, so I really have to keep the file size to a minimum to stop the ebook becoming unwieldy.

However, the book's main use is for printing, so the images have to be 300dpi to come out OK.

The smallest file sizes I can get are with gif's as there is only 2 colours involved. But whenever I save as .gif, it changes to 72 dpi.

So my questions are:

1) Is there anyway to make a 300 dpi gif?

2) If not, will a gif respond OK to being made 300/72 times bigger and then resized back down to the required size to get the resolution?

Or am I going about it all wrong :-)

Thanks for any help you can give,

All the Best

CY

 

mivox




msg:850138
 4:52 am on May 21, 2002 (gmt 0)

If it needs to be printed, you'd be better off using TIFF format. A 300ppi bitmap (B&W) TIFF shouldn't be TOO huge. Is it possible to have an "ebook version" and a "print version" with different image versions in each?

CromeYellow




msg:850139
 5:47 am on May 21, 2002 (gmt 0)

Hi Mivox

Thanks for the quick reply.

I've given it a go in tiff format and it's bigger than the jpeg.

The ebook is only of use when it is printed, so I've got to go for the 300dpi thing.

Hmm...

Thanks

CY

CromeYellow




msg:850140
 7:55 pm on May 21, 2002 (gmt 0)

Does anyone know about this?

"2) If not, will a gif respond OK to being made 300/72 times bigger and then resized back down to the required size to get the resolution?"

If I had a printer I would print it off and see. I don't :-(

Cheers

CY

mivox




msg:850141
 7:58 pm on May 21, 2002 (gmt 0)

I don't think you can create a gif in any resolution but 72ppi. At least not with any graphics software I've used...

What about BMP (bitmap) format? Have you tried that?

kingkelly




msg:850142
 8:07 pm on May 21, 2002 (gmt 0)

Bitmaps are even bigggggger... Im having the same prob.. My computer is slow, and am using Quark to put together a tiny 20 page book. I want the pictures on it to come out really nice, but if i use bmp or tiff, my comp will blow up, plus i still have to somehow bring it to the printshop. Right now im just using a big JPG (4500x1000) as the header, which will print out at 8.5"x2".

Will this turn out nicely?

tedster




msg:850143
 8:11 pm on May 21, 2002 (gmt 0)

You can save a tif file with LZW compression - it's the same "lossless" compression scheme used in the GIF format. The file size is about the same as GIF in that case.

Your idea for creating a GIF with larger dimensions and then resizing the image works with a browser - but I have never worked with ebooks, so I can't say for sure that this is your answer.

> The smallest file sizes I can get are with gif's as there is only 2 colours involved.

Now this is a major factor. With only 2 colors, unless the image lines are all perfectly horizontal and vertical, I'd imagine you will get the jaggies no matter what.

Are your source files only 2 color? Even if they look like two color to the eye, I'd suggest saving at 8 colors.

CromeYellow




msg:850144
 8:18 pm on May 21, 2002 (gmt 0)

Hi

It's nice to be in the same boat KingKelly - even if the one we're in is a bit leaky ;-)

Tedster - This is cool - you reckon a compressed TIFF might be the way to go. Excellent, I'll give it a try.

KingKelly - have you tried this with gif's? I'm not sure why you have to do this with a jpeg - can you not just make it the resolution you want?

Awaiting the next instalment with anticipation...

CY
I have been using 8-colour gif's and they look OK on the screen. Hopefully tomorrow I'll get a chance to print and see whether the old 'make em big and shrink em' technique works OK.

copongcopong




msg:850145
 4:17 am on May 23, 2002 (gmt 0)

as far as I could remember GIF was designed specifically for the web and since computer monitors do have 72 dpi (some have higher though), which may cause you to only have this option.

mivox




msg:850146
 4:46 pm on May 23, 2002 (gmt 0)

Welcome to the Graphics forum, copongcopong... that was my impression about gifs as well. One resolution to choose from. Like a Model T Ford: You can get it in any color you want, as long as it's black.

kingkelly




msg:850147
 12:16 am on May 24, 2002 (gmt 0)

Chrome: I use jpeg appose to gif since I do believe JPEGS have more colours than gifs. (gifs go up to 256 me thinks?)

Folks: To me, BMPs have the best image quality. Unfortuneatly, theyre bloody huge. Im using jpegs right now, but am thinking i should use Tiffs... Which is better? Why?

mivox




msg:850148
 12:24 am on May 24, 2002 (gmt 0)

Well, the original question specified B&W images, so JPG color resolution isn't really an issue...

TIF is a lossless image format... meaning it's bloody huge like BMPs. But, you can save TIFs in a compressed format (LZW compression I think) which saves some space.

JPG is a "lossy" image format, meaning the software saving the file discards image data it feels is unnecessary to the image. Every time you open and re-save a JPG you may be losing a little more of your image data, causing a long-term degradation in the quality of your file.

Which is why you should always keep a bloody huge "original" backup of any important images in a lossless format like TIF or BMP.

kingkelly




msg:850149
 5:06 pm on May 24, 2002 (gmt 0)

Thats bloody great!

Cheers!

tedster




msg:850150
 5:26 pm on May 24, 2002 (gmt 0)

> every time you open and re-save a JPG you may be losing a little more of your image data

Your on the money. The artifacts generate more artifacts and pretty soon...eecccch!

We were talking about the Pegasus editor here a while ago. One of its excellent features is the ability to open a jpg and flip it, or rotate it, and even crop it - all without degrading the image.

It does this by moving the actual data directly in the file, rather than decompressing the image, manipulating, and then recompressing the image, artifacts and all.

This is a trick that Photoshop can't do (well, I haven't checked out v.7 yet) and one that it darned well should. Pegasus has saved me lots of time when clients send jpg scans of slides but have them oriented incorrectly.

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