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Post by hallucygenia on May 18, 2005 15:53:00 GMT -5
Not really a photography question this, but I've been wondering about this for a while. What sort of resolution is it best to scan photos at for a website or slide show? My problem is that something can look fine on a normal size computer screen, and so would presumably be OK on a website, but I don't know how that would translate onto a large screen for a talk. I think I usually end up scanning at far too high a resolution, just to be on the safe side, which leads to very big powerpoint files.
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Post by Roy on May 18, 2005 17:52:56 GMT -5
Hi Lucy,
I think there are a number of things to consider here, but let's deal with the resolution of images for the web or a data projector first. Images intended to be viewed in a website need only to be 72 dpi (dots per inch also ppi - pixels per inch) which will look fine on your monitor.
If you intend images to be downloaded and printed via let's say an inkjet printer, then you should aim for a resolution of at least 150 dpi at the actual size of the intended print - higher resolution will of course give better print reults.
Another useful tip is that as you increase the size of an image by a factor of 100% the resolution is correspondingly halved (or doubled if you reduce the image size). For example an A3 image at 72dpi will reduce to A4 at a resolution of 144dpi and then A5 at 288dpi and so on.
As for data projectors, the majority on the market at present are SVGA, or "800 x 600pixels" at 72dpi - This is a very popular resolution today, because of their attractive prices and great images. <br> XGA, or "1,024 x 768pixels" - XGA projectors are generally more expensive, and are an equally popular resolution format to SVGA. They have become more popular as XGA resolution computers have become more plentiful. <br> SXGA, or "1,280 x 1,024" - SXGA products are high resolution, and notably more expensive than XGA. These products are targeted for high end personal computer users and low end workstation users. They are used primarily for command and control, engineering and CAD/CAM applications where acute resolution of small details is important. <br> UXGA, or "1,600 x 1,200" - UXGA is for very high resolution workstation applications that are detail or information intensive. These are expensive projectors that support a broad range of computer equipment. Relatively few products on the market have this native resolution. <br> In summary then I would say that the following factors will decide the resolution of your scans:
1. Thinking ahead - will you ever need to print the images you are scanning, and if so what size would you like to print them?. Lets say you decide that the A5 photograph you are scanning for your data projector slide show will also be printed in your forthcoming book at A4. Then the best thing to do would be to scan the photo at 600dpi and resize to A4 at 300dpi and then resize to a size of 1024 x 768 pixels at 72dpi for your slide show. That way you will only have to scan the image once!.
2. File format - as above, if you are going to print from the image then it is best policy to save it as a .tiff file. If you know you will only ever use it for a slide show then .jpg files with medium compression are sufficient and will be a much smaller filesize.
3. Colour or Black and white - If your image is a monochrome photograph and you would only want to present it as true black and white (ie.not sepia toned) then you only need to scan the image as a greyscale image. Colour RGB or CMYK scans contain much more data to render the colour in the image and by choosing to scan as a greyscale you will save up to two thirds of the file size. If your image is a line drawing then choose to scan it as 'Line Art' and even at a resolution of 1000dpi (recommended for print) the file size will be very small.
If you have access to Adobe Photoshop or a similar image editing software, you can always scale an image down in size to svga resolution. The problem comes when you have an image scanned at 72dpi and you need to print it at twice the size - the image will be very pixellated and have a blurred appearance.
Finally, as you mentioned Microsoft Powerpoint as a slideshow presentation package - the latest versions of Powerpoint have a facility to compress the completed presentation, which can be helpful if you need to email or ftp the file to someone.
Phew....
I'm sure I've forgotten something but those are the main guidelines for scanning resolution. It's a pretty wide subject really - there are so many different types of scanners, file formats etc. but we can cross those bridges when we come to them as they say......
BFN.
Roy.
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