Scanned Image Format - Which Is Better

[omorah]

There has been some issues on what format is better or best for some kind of work in AutoCAD. For a Civil Engineering business, we sometimes scan maps to use as background or to enlarge to about twice the original size. But in about 90% of the times, it is just scanned to it's original size.

Some of the issues are:
1. What format should maps be scanned into?
2. Since we don't use Raster Design in my office, is it worth scanning into TIFF?
3. As in video or audio, AVI and WAV are larger files and unnecessary, while MPEG and MP3 would give a very perfect result that no human ear would notice
the difference.
4. Does the JPEG file lose it's quality so much that the quality of the file WILL lose it's quality after some years?
5. What is wrong in scanning a D-Size color map sheet in 200dpi-400dpi, in JPG, with long shelf life in mind?
Thanks

[Railrose]

Here is an excerpt from the Raster Design ATP class we just finished. Maybe it will help answer your question.

Dots per inch (DPI) is usually set for between 200 & 400. Since the cost of memory is dropping so much, we use 400 for bitonal images. It allows more detail in the image making it easier to complete lines & get text that can be read. Color & grayscale drawings may require a higher DPI of 600. Anything more is probably a waste of resources, including handling speed of the computer. The best test of whether the DPI is set properly, the average line in the drawing should be 2-3 pixels wide.
Next, is the matter of image formatting. TIFF is a good general-purpose format. It works well with compressed bitonal images. CCITT Group4 compression is well documented & works with most applications. It creates a high degree of compression. JPG formats can lose a lot of information during compression on bitonal images. It can render text & details as totally useless.

[arshiel88]

The file format depends on where you will use it and how you will use it. For bitonal, definitely TIFF. Bitonal images when inserted to autocad will adapt color that you set on it in AutoCAD. cool isnt it? JPEG on the other hand can have a higher compression, you can fade the image via image properties, but will not adapt autocad color since JPG is always a TrueColor and never a bitonal image. 32 bit TGA for rendered images, this will be able to store Alpha Channel.

On the size/dots per inch (dpi). This is relative to the computer you are using (at least in my experience and humble opinion). In the office I use a very old P4 2.20Mhz with 768MB RAM with 64MB VGA Card; and 300-400dpi images takes me forever to regen. (sigh, I hope my boss can read this. ) By experience, since we're dealing with big images, i dont have problems with 150dpi, but never ever use <=72dpi images for printing.For raster images, Quality is lost in resizing down and resizing up wont take it back.

On the Quality with regards to time (long shelf life), this will be with respect to technology. If I scan an image for 300dpi(which is fine) today and keep it for so many years, it will stay 'fine' as time goes by. But if you will compare it in relation to the more advanced solution, maybe the 'fine' for the past years may only be 'not bad' for the next years.

[jaberwok]

One thing to watch out for is that there are several flavours of TIFF. AutoCAD does not support all of them.

[omorah]

Thanks everyone for the great replies. Very interesting. I would like more information.
As in the first post, what happens (comparably) if the same image is scanned with the same properties, say 300x300, and the same compression, what will happen to the "shelf-life" of this image?

My issue here is that some of my co-workers would scan sheets in TIFF and end up with files as large as 40MB to 300MB. Is this really worth the waste of hard drive space on the network, if the same sheet can be scan in JPG in good resolution and still have really good result.

I am not saying that TIFF should be a second choice, but the issue is that it usually defaults to higher file size since most user don't bother to change the file-format setting before scanning.

Another question I would like answered is if a file's shelf-life is greatly altered after some years. Yes I am sure something happens to every file, but is it really significant to worry? I don't believe so.

[Railrose]

Thanks everyone for the great replies. Very interesting. I would like more information.
As in the first post, what happens (comparably) if the same image is scanned with the same properties, say 300x300, and the same compression, what will happen to the "shelf-life" of this image?

My issue here is that some of my co-workers would scan sheets in TIFF and end up with files as large as 40MB to 300MB. Is this really worth the waste of hard drive space on the network, if the same sheet can be scan in JPG in good resolution and still have really good result.

I am not saying that TIFF should be a second choice, but the issue is that it usually defaults to higher file size since most user don't bother to change the file-format setting before scanning.

Another question I would like answered is if a file's shelf-life is greatly altered after some years. Yes I am sure something happens to every file, but is it really significant to worry? I don't believe so.

As mentioned earlier, shelf life isn't much of an issue. It's more of the ability of the processors to better deal with the images with the improvement of technology. I wish we had a crystal ball to see what computers will handle 10 years from now. I work with images that were scanned 7 years ago. There is no difference in the image quality, just the software that can handle it. The only differences are in which ones lose quality when changing formats from something like jpg or tiff to pdf. All I can suggest is scan an image to different formats & compare the current quality & file size.

[omorah]

Thanks Drafter29 for your insight.
My goal is to explain to my co-workers that it really does not mater what format an image is scanned, I feel that what matters is how it is originally scanned. Persoanlly, I prefer to use JPEG, with a good JPEG's good property settings before the scanning.

As in video (AVI) and audio (WAVE) these files can sometimes be very large. If I can achieve a good result for the average human ear with a MP3 or WMA, why not? This is exactly my point to my collegues.
Thanks again.

[scott.wilcox]

Personally, I prefer PNG, since it offers lossless compression. The size of JPG, the quality of TIFF.

[Ed Jobe]

PNG is a good choice and is generally considered superior to jpg. "Shelf life" however, is not a consideration of degradation, like film fading. Things that might affect the life of the file a common to any long term data storage. Will the file still be there when you want it? Standards can fall out of grace and become replaced by new ones. However, you can usually convert formats at any time. Another consideration is editing. What formats does your editor support? Raster Design is a good program for use in acad, but is limited in the number of file formats it supports.