Shine Gonzalvez wrote:can someone explain the following....for printing pics i am using 300dpi...for uploading onto this forum i am using 72 dpi.....
I understand one file sae is bigger than the other..
1) why does there appear to be no loss of definition when reducing dpi to 72
2)what would happen if i got pics blown up and printed in 72dpi
3)if i was uploading a pic to Facebook what dpi should i use and why?
4) are any other dpi"s i should be considering and when should i use them and why
thanks in advance
5)does dpi have an affect on distortion of a pic
6) when should i not check the resample image box
thanks in advance
Shine, the problem is directly related to the destination of the image. On Displays
, they typically have between 72 and 96 pixels per inch. There will be little difference between monitors. The image size will change on screen only if you go from a small to a large monitor or from monitors with different resolutions.For example, I have an NEC 26" with a resolution 1920(w) x 1200(h). My monitor for retouching is my 27" Eizo with a resolution of 2560(w) x 1440(h). At pM we suggest 1700 pixels on the long side. Now, a pixel has a physical size. The information in the pixel though has no physical size. It can be small or large depending on the use. Monitor pixels do have a physical size all different depending on the quality etc. If I have a landscape image at 1700 pixels on the horizontal, we can see that both monitors will display the full image with using scroll bars. If we change the horizontal pixels to 2300, my eizo will still display the full image, however, now my nec won't and will use scroll bars to see the full image. So, monitor size AND the display resolution affect how the image is displayed.For Print
, it depends.. Due to the method of manufacture, differrent printer makers have different native resolutions. Native means what the printer will actually print at regardless of the ppi you send it. For my Epson printer its native resolution is 360ppi. This means that 360 pixels in the image will be printed in one inch. Of course, there will be much more to it than that but this is a simple explanation. If I send it an image at 180 ppi, the printer has to interpolate (makeup essentially) the inbetween bits of data to make it fit the 360 dpi. So, since my printer prints at 360dpi, if I send it an image at 180ppi, it makes up information and resamples it on the fly. It means that the PHYSICAL size of the print will be twice as big. This is because now we are talking actual physical sizes, as opposed to displays. If you send a 72 dpi image to a printer, the printer will print it 5 times larger than if the same image had been sent as 360ppi. 360/5 = 5
As a result of my printers native resolution of 360ppi, I set my Camera Raw and Photoshop/Lightroom prefernces to 360 ppi as well. This then gives me the correct size of the print automatically in the software.
For example, I have an image below. 3744x5616 pixels. At 360 ppi, the print size is 10.4" x 15.6"
However, by NOT resampling and telling PS that the resolution is 300ppi (for Canon and most other printers) we see that the same image not altered apart from changing the ppi willl print out at 12.48" x 18.72"
The fun starts when we want to print at my printers native resolution of 360ppi. AND I want it larger than 10"x 15". I could leave it to the printer to do that BUT, I feel that if I resize it myself in PS, I have control over the resizing, rather than the print driver which does a soso job.
In the image below, you can see that I specified a print 22" wide AND specified the 360ppi. The only thing that could then be changed was the number of pizels required. PS as a result worked out that for an image 22" wide, I needed 7920 pixels instead of the original 3744 pixels.
In the image below, I specified a print width of 22" and deselected the Resample checkbox. This resulted in the ppi dropping to 170.182 instead of 360. However, this will now be resized by the print driver which is not what I want.
Q1) why does there appear to be no loss of definition when reducing dpi to 72
For displays, the image is not changed whether it is set to 72 or 300 dpi. It is irrevelant for displays. Only printers.
Q2), what would happen if i got pics blown up and printed in 72dpi?
Depending on how the image is printed you MAY end up with very large images. It does depend on how you set the software up.
Q3) if i was uploading a pic to Facebook what dpi should i use and why?
Again, it's irrevelant. I use 1920 x 1080 in LR for export to FB. On High Def 1920x1080 displays, the picture can be shown full size without FB screwing it up. Others suggest different numbers. I use this and it works.
Q4) are any other dpi"s i should be considering and when should i use them and why.
DPIs are for printing use. Set your Epson to 360 in software. eg, LR, ACR and PS. For Canon and most others, set it to 300. Check your printer documentation to confirm the native resolution.
Q5) does dpi have an affect on distortion of a pic?
No, aspect ratio does, an image 3" wide and 2" tall has an aspect raio of 3:2. If you CHANGE that ratio, it will distort the image. Otherwise, PS and LR are pretty smart on resizing and will keep the aspect ratio of the image.
Q6) when should i not check the resample image box?
When you want to lower the ppi and have the printer do the resizing for you. I don't recomend this.