Pixels..

I can understand losing pixels when an image is cropped but I don't understand losing pixels when an image is down sized.When an image is cropped ,a part of it thrown away so some pixels are lost.But when down sizing an image ,there are no parts of the image which are thrown away,so what happens to the pixels ,why are they lost?
And if some pixels are lost because of down sizing,does it mean that the image quality gets worse?

Simple Binnur - my camera has a sensor that captures 7360 x 4912 (36MP). My computer display is 1920 x 1280 (about 2MP); than means every time I render an image on my computer screen, I am effectively throwing away 34MP. In this case, the "throwiing away" is temporary, as the original file still exists, and the downsampling occurs only while the image is displayed

If you download a file to photo site; even more and I use the same size as per my screen, then these pixels are actually "thrown away" permanently as the image that is stored at these sites will be at the reduced image size.

Thank you Manfred,what if I down size a file in my computer ,in this case do I still throw away the pixels and do I lose the original file?

Quote:

---

Originally Posted by GrumpyDiver

Simple Binnur - my camera has a sensor that captures 7360 x 4912 (36MP). My computer display is 1920 x 1280 (about 2MP); than means every time I render an image on my computer screen, I am effectively throwing away 34MP. In this case, the "throwiing away" is temporary, as the original file still exists, and the downsampling occurs only while the image is displayed

If you download a file to photo site; even more and I use the same size as per my screen, then these pixels are actually "thrown away" permanently as the image that is stored at these sites will be at the reduced image size.

---

If you overwrite the original file (i.e. use the same filename as the original), yes. If you give it a new filename, then no, you will still have the original file.

Quote:

---

Originally Posted by bnnrcn

I can understand losing pixels when an image is cropped but I don't understand losing pixels when an image is down sized.When an image is cropped ,a part of it thrown away so some pixels are lost.But when down sizing an image ,there are no parts of the image which are thrown away,so what happens to the pixels ,why are they lost?
And if some pixels are lost because of down sizing,does it mean that the image quality gets worse?

---

Hi Binnur

When you downsize an image, you effectively replace the original set of pixels with a new (smaller) set of pixels. Each pixel in the smaller sized image is estimated from several pixel values from the original image. There is a loss of resolution that will show up if you enlarge the image substantially.

You would normally keep the original file and save the downsized version as a separate file.

Dave

So what is the optimum file size for a proper photograph Manfred? We keep downsizing or enlarging our photos but there has to be an optimum size.

Quote:

---

Originally Posted by GrumpyDiver

If you overwrite the original file (i.e. use the same filename as the original), yes. If you give it a new filename, then no, you will still have the original file.

---

Thank you Dave:)

Quote:

---

Originally Posted by dje

Hi Binnur

When you downsize an image, you effectively replace the original set of pixels with a new (smaller) set of pixels. Each pixel in the smaller sized image is estimated from several pixel values from the original image. There is a loss of resolution that will show up if you enlarge the image substantially.

You would normally keep the original file and save the downsized version as a separate file.

Dave

---

There really is no such thing as optimal size, as it depends on your final use. The optimal size to display an image on your phone's screen is going to be a lot different from if you were planning to print an image to 1m x 2m. In fact, if I look at my images and were to print them on my photo printer at full native resolution (i.e. 36MP at 360ppi / 142 pixels / cm), I would end up with an image that is approximately 20cm x 30 cm.

If you are saving images out of your camera; save the best quality image you can, as that lets you rework the image to final the final size. I always work my images at full native resolution and then create the output from that edited file.

What I understand from your explanation is that the image quality also depends on your camera's capability.My camera shoots photos in 4272x2848 pixels ,so my photos are much more affected by cropping or by enlarging than yours because they have already less pixels.Is it correct?

Quote:

---

Originally Posted by GrumpyDiver

There really is no such thing as optimal size, as it depends on your final use. The optimal size to display an image on your phone's screen is going to be a lot different from if you were planning to print an image to 1m x 2m. In fact, if I look at my images and were to print them on my photo printer at full native resolution (i.e. 36MP at 360ppi / 142 pixels / cm), I would end up with an image that is approximately 20cm x 30 cm.

If you are saving images out of your camera; save the best quality image you can, as that lets you rework the image to final the final size. I always work my images at full native resolution and then create the output from that edited file.

---

Quote:

---

Originally Posted by bnnrcn

What I understand from your explanation is that the image quality also depends on your camera's capability.My camera shoots photos in 4272x2848 pixels ,so my photos are much more affected by cropping or by enlarging than yours because they have already less pixels.Is it correct?

---

At a high level, that is correct, but it's really a lot more complex than that. First of all; I am shooting a full-frame image, while your camera is a crop frame; so that comes into play.

The other key issue is (again) the final image size. If we are preparing an image for a Smartphone, the difference would not be as great as if we were looking to to a large print.

Binnur, a good practice is to always leave your photos at full resolution until you prepare them for their final display. For instance, I would recommend downloading photos from your camera, making copies of the ones you want to edit, and edit the copies. That way you always have a full-resolution, untouched original file to return to if the edit goes badly.

For me, downsizing is the last step. How far I downsize depends on where the image will be displayed. 960px wide or high (whichever is longer) looks good on Facebook. But for prints, I would use the full available resolution.

I agree with Lex. I would put it this way: only reduce the size of the file when you have a need to. For example, if you are going to display on the web, you have to downsize because the resolution of computer screens is so much lower than the number of pixels in a full image from a modern camera. You have to downsize to attach a file to e-mail. For printing, there is rarely a reason to downsize. If you print yourself, good software will take care of this for you. If you send to a lab, ask them. I print most of my own, but when I don't, I use Bay Photo here in the US, and they ask specifically that you send them the largest file you can.

When I do need to downsize, I keep the full-size image as well.

Thank you Lex and Dan,I'm quite clear about the subject now and I will keep the advices in mind:)