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  1. #11
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    Default Re: Fuzzy pictures in slideshow

    [QUOTE=gwpriester;522704]Yeah, I hear you, Paul. My thinking is when you export an image from Xara at 96dpi with a zoom factor of 100% it is 1:1 and should appear at the same size and resolution when you see it in a browser./quote]
    My suggestion is that the browser couldn't care less what the dpi is. All browsers care about are pixel dimensions.

    Ah, maybe it was this. For print, what matters is the actual pixel dimensions. So if I export an image that on the screen is 960 x 768 at 300ppi the actual size in pixels is 10" x 8". But if I take the same image an post it on the web, the size is 3000 x 2400 pixels, larger than most monitors
    yes, that's because for print purposes you specify a physical size and the number of pixels to create per inch.

    I think I'm failing to get across that dpi is irrelevant online. Pixel dimensions rule online and dpi is totally ignored for images and doesn't exist in some formats.

  2. #12
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    Default Re: Fuzzy pictures in slideshow

    I think I'm failing to get across that dpi is irrelevant online. Pixel dimensions rule online and dpi is totally ignored for images and doesn't exist in some formats.
    Exactly, dpi is meaningless. Pixel size is all that matters.
    Egg

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  3. #13
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    Default Re: Fuzzy pictures in slideshow

    I think what does really cause confusion is that people prepare print documents and then want to output bitmaps that satisfy the print requirements and these are expressed in DPI for the physical medium. So the 4inch square print image is going to be exported from Xara at perhaps 300DPI resulting in an exported image 1200pixels wide and high with (depending on the format) a DPI setting of 300.

    On the web and in the digital display world DPI doesn't matter at all. So that 4" image in print is just a 1200pixel wide image.

    On my screen, which has by default a 1440 pixel width, it will almost fill the screen horizontally and be too tall to see the bottom. On other people's screens it will be different physical sizes according to their display.

    If we had a document set up with pixel sizes rather than physical ones, then DPI has no relevance at all. When exporting for a web page, the DPI has no relevance for display. If you were exporting an image for print or re-import to a print document, then DPI is then important again, because when importing an image the only way to know what physical size the image represents in a print document is the DPI setting and the pixel size.

  4. #14
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    Default Re: Fuzzy pictures in slideshow

    I don't understand how dpi cannot be relevant for images on the web. I've attached a number of images - these were from hi res tiffs - the first is an image 100mm wide @ 300dpi and the second 100mm wide @100dpi - both resized in PS and saved as quality 10 jpgs. The third image - a screen capture, shows both images at 100% - obviously the one is larger, but the quality of the images appears to be the same. The last screen capture shows both images at the same size on screen with a vast difference in quality. So if you want high quality images on your website viewed at a certain size, the dpi of the images is very important.

    Click image for larger version. 

Name:	300dpi 100mm.jpg 
Views:	121 
Size:	72.1 KB 
ID:	106334Click image for larger version. 

Name:	100dpi 100mm.jpg 
Views:	132 
Size:	70.3 KB 
ID:	106333Click image for larger version. 

Name:	100%.jpg 
Views:	126 
Size:	62.4 KB 
ID:	106332Click image for larger version. 

Name:	same size.jpg 
Views:	127 
Size:	88.2 KB 
ID:	106335

  5. #15

    Default Re: Fuzzy pictures in slideshow

    Did you read through this article posted earlier?
    I might help clear things up.
    PS: Xara use DPI but really mean PPI.

    http://www.scantips.com/no72dpi.html

  6. #16
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    Default Re: Fuzzy pictures in slideshow

    Quote Originally Posted by letsgofishing View Post
    I don't understand how dpi cannot be relevant for images on the web.
    Checkout Steve's link.



    the first is an image 100mm wide @ 300dpi and the second 100mm wide @100dpi - both resized in PS and saved as quality 10 jpgs.
    I think this is core to the problem people have with DPI.

    You explain that the images have physical a size - 100mm. This is only possible because your document has a notional physical size because it represents a tangible physical medium, such as a sheet of paper. Photoshop is representing a physical medium on the screen.

    When you export these images for printing on the paper, the quality of the image when printed depends on the physical properties of the printer and the amount of detail present in the image. A typical choice during export is 300DPI, which means that for every physical inch that you wish to print, the software will provide 300pixels. For a less detailed print, 100DPI will provide 100pixels for each inch of the image according to the size you have made it.

    So, the export process is taking a physical size, destined for a physical medium, using the DPI setting to create an image with enough pixels to print at the quality that you have specified. So the DPI setting changes the pixel size of the image.

    When it comes to showing those same images on a computer screen, the representation of the image is no longer related to the original physical size in the document, but is simply the pixel dimensions that the image was saved at. The computer does not look for DPI information it simply looks at the pixel size. Any DPI information is ignored.

    Your watch example has images varying in size because photoshop is combining the physical size that has been specified, with the picture density that you require for printing, to create an image of the correct pixel size to facilitate printing.

    If your computer screen took notice of DPI, then all of the watch images would appear at the same size. They all vary in size because the screen is only interested in pixel sizes. Many image formats do not have DPI information stored in them at all.

    DPI is important for the export process when translating a physical measurement into a pixel size. After that it doesn't matter as far as screen displays are concerned.

  7. #17
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    Default Re: Fuzzy pictures in slideshow

    Quote Originally Posted by pauland View Post
    Checkout Steve's link.





    I think this is core to the problem people have with DPI.

    You explain that the images have physical a size - 100mm. This is only possible because your document has a notional physical size because it represents a tangible physical medium, such as a sheet of paper. Photoshop is representing a physical medium on the screen.

    When you export these images for printing on the paper, the quality of the image when printed depends on the physical properties of the printer and the amount of detail present in the image. A typical choice during export is 300DPI, which means that for every physical inch that you wish to print, the software will provide 300pixels. For a less detailed print, 100DPI will provide 100pixels for each inch of the image according to the size you have made it.

    So, the export process is taking a physical size, destined for a physical medium, using the DPI setting to create an image with enough pixels to print at the quality that you have specified. So the DPI setting changes the pixel size of the image.

    When it comes to showing those same images on a computer screen, the representation of the image is no longer related to the original physical size in the document, but is simply the pixel dimensions that the image was saved at. The computer does not look for DPI information it simply looks at the pixel size. Any DPI information is ignored.

    Your watch example has images varying in size because photoshop is combining the physical size that has been specified, with the picture density that you require for printing, to create an image of the correct pixel size to facilitate printing.

    If your computer screen took notice of DPI, then all of the watch images would appear at the same size. They all vary in size because the screen is only interested in pixel sizes. Many image formats do not have DPI information stored in them at all.

    DPI is important for the export process when translating a physical measurement into a pixel size. After that it doesn't matter as far as screen displays are concerned.
    Many thanks for that explanation Pauland....

 

 

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