Reflection ( Week 13 : 30 Mac 2011 )

Case Study 2 (the horrible dpi mistake)

What is resolution? 

In desktop publishing, resolution refers to :

1. dots of ink that make up a picture when it is printed on paper ( 300 dpi - 2400 dpi)

2. electronic pixels when displayed on screen (72 dpi -  96 dpi)

What is dpi?

1. number dots of horizontal and vertical per inch.

2. familiar term by printer, scanner @ digital camera.

3. measure of resolution.

4. measure of how a image is printed to a medium such as paper or scanned paper.

* Each type of display device has a maximum number of dots it can process and display no matter how many dots in the picture

* Example: 


  Laser printer : 600 dpi
  Windows computer monitor : 96 dpi
  Mac computer monitor : 72 dpi

* So, when picture has more dots than the display device can support :

  - the dots wasted
  - increase file size but do not improve the printing or display picture
  - Example:

    Laser printer : 300 dpi and 600 dpi
    Result : same quality printed but 600 dpi has larger file.

* So, when picture has fewerr dots that display can support:

   - picture not clear & sharp.
   - Example :

     Picture on web 96 or 72 dpi (resolution of computer monitor). If print a     
     72  dpi picture to a 600 dpi printer, NOT GOOD as in computer monitor       
     because printer does not have enough dot's of information to create a       
     clear and sharp image.  

4 main factors that determine image quality?



1. the quality of the recording device (camera optics and sensor, scanner's sensor)

2. the size (in pixels) of the digital image.


3. the digital format it is stored (lossless vs lossy compression)

4. the technical proficiency and the 'eye' of photographer. 

What print shops really mean by dpi?


> Print shops asked for a digital photo at 300 dpi means the photo that the photo will print at a certain paper dimension in inches at 300 pixel per inch PPI.


How to changes the dpi?


Adobe Photoshop  Method.


1. Load your image into Adobe Photoshop.


2. Select the "Image > Image Size" @ "Image > Resize > Image Size"


3. In the image size dialog window, deselect the "Resample Image" checkbox. (make sure the is no checkmark in that box)

4. In the "Resolution" box type in 300 (or whatever dpi you want).


5. Click "OK button".


6. Your image dpi has now been set to whatever you want (leaving the pixel dimension of the image unchanged)


7. Save the photo with a new name.


(this procedure change the dpi setting but size and resolution will be unchanged)