Scanning Tips

[Shannon]

• Printing - 150 to 300 dpi
• Web, PowerPoint presentations, email: 72dpi
• Line art: 300 to 600dpi
• High-quality photo archives: 300 to 600dpi. Keep in mind high-resolution images occupy a lot of space both in RAM and on disk.

 

[GilesGuthrie]

This is all dependent upon the ratio of original image size : final image size being 1:1. If you are changing the size, you need to change the resolution accordingly. Also, you're almost, but not quite there on the general philosophy.

Your scan resolution is dependent upon your output device resolution, not your input device resolution. This is where you get your figures from, but they're not as black and white as you make out. For example, if you're printing to a 2400dpi printer, you absolutely don't want to scan at 150dpi.

So, your scan resolution should be:
Output device resolution x size alteration.

Also, if you are genuinely scanning for high-quality photo archives, you should scan at the maximum resolution possible, since you don't know the final destination of the image, or indeed how much of your image will be used. If the user wishes to extract a small detail from your image, it will be no use if you have scanned at a lower resolution, because once they have picked their part and enlarged it, your resolution will have fallen dramatically.

I scan photo negatives at 2900dpi, which is equivalent to 12MP on a 35mm frame. This way I can print A4-size at over 600dpi without an issue. Each compressed TIFF file is 35MB.

I'd be interested to hear your views on image file formats - their strengths, weaknesses, and suitable uses.

 

[Shannon]

Originally posted by GilesGuthrie
This is all dependent upon the ratio of original image size : final image size being 1:1. If you are changing the size, you need to change the resolution accordingly. Also, you're almost, but not quite there on the general philosophy.

Your scan resolution is dependent upon your output device resolution, not your input device resolution. This is where you get your figures from, but they're not as black and white as you make out. For example, if you're printing to a 2400dpi printer, you absolutely don't want to scan at 150dpi.

So, your scan resolution should be:
Output device resolution x size alteration.

Also, if you are genuinely scanning for high-quality photo archives, you should scan at the maximum resolution possible, since you don't know the final destination of the image, or indeed how much of your image will be used. If the user wishes to extract a small detail from your image, it will be no use if you have scanned at a lower resolution, because once they have picked their part and enlarged it, your resolution will have fallen dramatically.

I scan photo negatives at 2900dpi, which is equivalent to 12MP on a 35mm frame. This way I can print A4-size at over 600dpi without an issue. Each compressed TIFF file is 35MB.

I'd be interested to hear your views on image file formats - their strengths, weaknesses, and suitable uses.

Cool.

Well, I just got that out of a magazine (Australian PC User) and posted it here....

As for my views on image file formats, I prefer jpg as I can put them up on the web and they don't take up much file space. Although, JPG is a lossy file and the more you save a JPG image, the more image quality you use. I try to stay away from GIFs as they are absolutely crap, but as we all know, for animations you need to save it as a Graphics Interchange Format. TIFF (Tagged Image File Format) file formats are good if you have harddrive space to burn. TIFFS are not a lossy file format like JPG but generally use no compression. But my favourite file format so far has to be PSD (Photoshop) but the file size of PSD's are huge. The good thing though, is it keeps your layers so when you open that image up in Photoshop again you can still edit your layers. As, if you save it as another file format (JPG for example) all your layers are merged and all you have when you reopen it is a background.

I think JPG/JPEG's should be only used for web, along with Compuserve GIF and TIFF for print.