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Thread: Joining a matrix of tiles to make digital map

  1. #11

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    Quote Originally Posted by Bhikkhu Pesala View Post
    How is this ever going to work?

    How big are these images that you're joining? If 1,000 x 1,000 pixels, that is 1 Megapixel. An image of one million megapixels is not going to load in IrfanView. Even those high resolution NASA images are only 256 Megapixels.
    Hi B,

    I don't know how, but I'm sure it can be done, people are doing it all of the time.

    In my first message I asked for command line, or scripts, so perhaps it is done by compressing as it proceeds. The finished image of 1,00,000, images won't be megapixels, but much smaller.
    Cheers, C.

  2. #12
    Moderator Enterprise User Bhikkhu Pesala's Avatar
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    Pixels cannot be compressed. If you discard pixels you must lose resolution. PNG compression is pretty good, especially with images with few colours, which is likely to be the case with your (Google Map?) images. However, that reduces the size of the image on disk, not in memory. To reduce the RAM needed one can either reduce colour-depth or reduce resolution; either way one loses data.

    How big are the images being joined together? If they are a typical screen shot, they may well be more than 1 Megapixel.

    Click image for larger version. 

Name:	1 Megapixel Image.png 
Views:	6 
Size:	12.2 KB 
ID:	5690

    Perhaps someone will pass by who is good at writing batch files, but first let's discover if your project is even feasible.

  3. #13

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    Quote Originally Posted by Bhikkhu Pesala View Post
    Pixels cannot be compressed. If you discard pixels you must lose resolution. PNG compression is pretty good, especially with images with few colours, which is likely to be the case with your (Google Map?) images. However, that reduces the size of the image on disk, not in memory. To reduce the RAM needed one can either reduce colour-depth or reduce resolution; either way one loses data.

    How big are the images being joined together? If they are a typical screen shot, they may well be more than 1 Megapixel.

    Click image for larger version. 

Name:	1 Megapixel Image.png 
Views:	6 
Size:	12.2 KB 
ID:	5690

    Perhaps someone will pass by who is good at writing batch files, but first let's discover if your project is even feasible.
    Hi B,
    I'm not so good at this sort of thing, and always need help for this sort of 'blockage' to my ideas.

    As well as asking forums etc, I have a mate who's also trying. He's a bit more savvy, than me. I give him feedback as I get more information, and he says he's writing an algorithm? and I notice his explanation includes re-sizing plus some other 'clever' words.

    I opened one image in Irfanview, then saved it as a JPG. Here it is:
    C
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	1 image.jpg 
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Size:	12.1 KB 
ID:	5692  

  4. #14
    Moderator Enterprise User Bhikkhu Pesala's Avatar
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    Even at 256 pixels, which is 16 squares to a megapixel, your final image will be 1 million/16 = 62,500 Megapixels. I think you're unlikely to succeed and will end up breaking your country into a thousand strips of 62.5 Megapixels.

    Saving as JPG just reduces the quality and increases the file size for such images. Use PNG instead, it will be smaller on disk. By reducing the colours to 256 very little colour information is likely to be lost. The attached image is only 7.55 Kbytes on disk, although the same dimensions as your image, which is 12.15 Kbytes on disk.

    Click image for larger version. 

Name:	256 pixel image.png 
Views:	5 
Size:	7.6 KB 
ID:	5694
    Last edited by Bhikkhu Pesala; 05.12.2019 at 10:31 AM.

  5. #15

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    Quote Originally Posted by Bhikkhu Pesala View Post
    Even at 256 pixels, which is 16 squares to a megapixel, your final image will be 1 million/16 = 62,500 Megapixels. I think you're unlikely to succeed and will end up breaking your country into a thousand strips of 62.5 Megapixels.

    Saving as JPG just reduces the quality and increases the file size for such images. Use PNG instead, it will be smaller on disk. By reducing the colours to 256 very little colour information is likely to be lost. The attached image is only 7.55 Kbytes on disk, although the same dimensions as your image, which is 12.15 Kbytes on disk.

    Click image for larger version. 

Name:	256 pixel image.png 
Views:	5 
Size:	7.6 KB 
ID:	5694
    Hi B,

    Ok.

    Let's see how my mate gets on.

    Thanks, C.

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