resize images without losing accuracy ?

Discussion in 'Digital Discussion & Q&A' started by kmool, May 29, 2007.

  1. kmool

    kmool TPF Noob!

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    Hi guys

    I am new here , so I really dono if this is the right place to post .

    I need to resize some images so that I can add them for a book .

    For example

    Original
    [​IMG]



    resized

    [​IMG]

    The problem is that the resized image is not readable ? any help so that I can resize and read the text ?

    Thank you
     
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    What software are you using to resize the image?
     
  3. fmw

    fmw No longer a newbie, moving up!

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    Some software will allow you to do what you want. Some will not. If yours will not, then you can resize a copy of the image and save the original for another time and another type of software.
     
  4. The_Traveler

    The_Traveler Completely Counter-dependent Supporting Member

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    You need to remember that you are viewing at 72 DPI and printing is done at 250 so it is crucial that you size the image so that it has enough pixels to print legibly at the actual dimensions you want.

    If the original is fully sized as we see it at 1254 - it will flow off the screen when viewed but will print at about 5 inches wide (at 250/bpi).
     
  5. EOS_JD

    EOS_JD TPF Noob!

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    When you resized I think you just selected the image and dragged in the corners.....right? It's better to resize by editing the number of pixels in the image file.

    Are you resizing to print or for viewing? If to view on the web, resize to 800 pixels on the longest edge. If for printing what size do you need the image to be?
     
  6. skieur

    skieur TPF Noob!

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    If you look at image size in Photoshop, PaintShop Pro or whatever editor you are using, it generally shows a large inch size as in 30 inches by 20 inches or whatever and 72 pixels per inch in another section.

    The approach is to up the pixels per inch as in change 72 to 300 ppi or whatever number that reduces the image size to about your printed page size as in 8 by 10 or perhaps smaller.

    The result is better printing quality and an appropriate image size.

    skieur
     
  7. EOS_JD

    EOS_JD TPF Noob!

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    You do not need to change the ppi at all. In a case above, just switch off resampling and change the image size to the size you want to print. The ppi will amend itself and so long as it is around 200ppi or higher it'll print perfectly fine. In fact the above image will probably print fine at less than 200ppi. Perhaps if it was a photo you may want higher if you were only printing a 10x8.

    What we need to know is the use you are putting the image to.
     
  8. skieur

    skieur TPF Noob!

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    When you switch off resampling you lock the aspect ratio or constrain proportions which does necessarily give you the print size you want, so this does not necessarily work. Adjusting the ppi, gets you closer to the size you want and with 8 by 10 when the image involves print 300ppi or greater would be best.

    skieur
     
  9. EOS_JD

    EOS_JD TPF Noob!

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    Best thing to do then is use the crop tool to adjust the aspect ratio. Set the image size you want (in inches, mm, pixels whatever) in the boxes at the top of the screen. Leave the resolution box blank to avoid interpolation.

    If you want a 10x8 just insert the figures into the boxes as 10in x 8in and drag the crop tool over your image. If you need a particular resolution (like 300ppi), you can also add this into the resolution box but be aware this will interpolate (up or down) your image.

    I prefer to leave the resolution blank because for small images up to 10x8 even with cropping I generally get more than the 240ppi-300ppi I require. For larger images, because they are viewed from slightly further away, you can print at much lower resolutions without any noticable drop in quality.

    I was sort of guessing the ratio of the above image wasn't going to change so that's why I didn't mention this earlier but using the crop tool is the easiest and quickest way to resize any image.

    The figure of 300ppi is described as the highest quality you need because your eyes can't resolve any higher than this figure (I'm led to believe) but as I noted above you can still print at lower resolutions and you'd be hard pushed to see any difference between 240ppi and 300ppi. the larger the print the further away it will be viewed and therefore the less the resolution can be. My 19"x13" prints are printed at 180ppi and look amazing. I can hardly see much difference even close up.

    Hope this helps.

    Regards
    Jim
     
  10. PatriK-b

    PatriK-b TPF Noob!

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    What you are showing here is a resize vs resample issue.

    There are many ways to change the size of a picture, we can categorize them in two categories:
    The first one, known as resize, used for exemple if you change the img size constraints in html, it just takes n pixels out of m if you want to resize from m to n.

    The second, will compute every pixels in the new image, as a mathematical result from several pixels in the source image. And here you will find different algorithms (splines, lanczos, hermite,...)

    First method should never be used, as you will get poor (but fast) results.

    Let's take an example:
    if you have a image with a b&w pattern of pixels: bwbwbwbw
    and you resize it to 50%
    you will get bbbb or wwww
    if you resample it to 50%
    you will get gggg where g=gray

    Independently of the algorithm you use, you will get a blur effect on resized text and lines because of edge smoothing by resampling algorithms.

    Ihih.
     
  11. skieur

    skieur TPF Noob!

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    Whether you can use the crop tool or not, depends on how close you can come to the correct aspect ratio without using it. Images with text such as the example at the beginning are not very flexible to being cropped. :wink:

    skieur
     
  12. EOS_JD

    EOS_JD TPF Noob!

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    Not sure what you are saying here but if I'm right it's the second one (resampling) that is the one you should avoid in your scenario. Resizing does not affect the original image (other than cropping some away).
     

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