Will I Lose Quality When Resizing Images?

Posted by David Peterson on 16 Feb 2007 as Image Files, Tips

I received this email a few weeks ago from Jennifer E, one of my subscribers:

“Hi David, I need to download some of my photos to a CD. My question is, if I resize the photos to a smaller size, so I can get more of them on my CD, then I reinstall them into my computer and size them to the size when I took the photo, will I lose any quality? (size 3264×2448 down to 640×480 then back up to 3264×2448) Thanks, Jennifer
P.S. Your books and info are great. Every time I go through them again, I always find something new. I am so glad I found you.”

Here’s my reply:

Hi Jennifer,

First off, thanks so much for your kind words. I’m really glad you’re enjoying my books!

Original image

The short answer to your question: Yes, you will lose image quality. If you resize your images down to a smaller size, and then size back up again, your image will be a lot less clear. When you resize the image back to the original size, you won’t get the original image back.

Why is this? The amount of detail stored in an image depends on two factors. The first is the number of mega pixels in the image. The more mega pixels, the more detail your photo has. That’s why newer model cameras boast larger mega pixel numbers – these cameras capture a more detailed photo.

The mega pixel count is (simply) the total number of pixels in the image, and thus is related to the number of pixels in the width and the height of the image (pixels wide times by pixels high equals the number of million (mega) pixels in the photo).

The same image after
resizing down and
back again.

By resizing the size of the image, you actually reduce the mega pixel count of the photo. When you reduce the megapixel count, the computer can’t store all the detail any more (there simply aren’t enough pixels to do so). In Jennifer’s example, she was reducing the size from 3264×2488 (8 megapixels) to 640×480 (about 0.3 megapixels). Thus removing detail from the image.

Resizing the photo back to 8 megapixels means there are a lot more pixels in the image again, but the computer no longer has all the pixels needed to reproduce the original image. So it copes the best it can and makes an approximation.

So to store images for the long term, do not resize your images to save space. You’ll lose valuable detail in your photos that you’ll never be able to get back.

Oh, the other factor that controls the amount of detail stored in an image is the method you use to store the photo. See my tip on file formats for more information.

So thanks for the question Jennifer.

If you have a photography related question that you’d like to ask, post it on the comments below and I’ll do my best to answer it for you!

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9 Responses

David Peterson says:

March 23, 2011 at 2:18 pm

Hi Peter,

That’s almost right. If you save a photo in most paint programs (CS included), it will overwrite the original. Something you don’t want. Also, even if you copy a layer with your original photo, it’s also changed when you resize or crop your changed layer.

To be absolutely sure, make a copy of the original file and only work on the copy.

David.
Peter Balacua says:

March 20, 2011 at 4:38 am

Hi David,

I have some comments regarding resizing an image. You said if you re- size an image you lost some of the pixels and you can’t never get them back to your original image.

Using adobe photoshop to edit your photos, you must have to doplicate your layer so that your original image is not affected. Nomatter you make your resize image bigger or smaller the original stays as it was.

Another thing is that if you use adobe lightroom, as soon as your images
are imported on the library module, you can edit your image into the
develop module. Here you can resize your image as well make it bigger
or smaller and you can always hit the reset botton to make another
adjustment on the size of your image without affecting the pixel of the
original image.

So Jennifer, just in case you find this comment try to experiment this
tip of mine. If you have adobe photoshop or adobe lightroom . As they
always say, don’t take my words for it.

Peter
Hasmukh says:

October 11, 2007 at 8:26 pm

Hi,
To re size the photo I use Photoshop. Simply open your photo in to photoshop and click image followed by image size then simply enter the size you want in the size box and click enter then save in diferent folder. Please make sure you always keep your original photo somewhere safe because just in case if you want your original size back then it is always there for you. Hope this will help.

Hasmukh Gohil
Margaret Spence says:

September 30, 2007 at 12:31 am

Thanks for this subject I need help. A 10 mega pixel is so large should I save to c d then resize the ones on computer? if so HOW DO I DO IT. Thanks for all your fab advice.
Amy says:

June 19, 2007 at 5:06 pm

When I want to resize, I usually save the resized file as another file in another folder, that way I have my original and something smaller to send to family, friends and to post them on websites. I then might save both photos on a CD (along with most of my other photos, resized and not) so I have more space on my computer. If I need more space on a CD for my photos (because they do take up a lot of space) I just buy another CD, or buy a whole stack.
Ramesh Panicker says:

February 23, 2007 at 6:48 pm

Can anybody tell me how to resize the image taken by 3.2 mega pixel camera to 4″x6″( size in inches) for developing prints.
which software to use and the method please without losing image quality
Gary Lucken says:

February 20, 2007 at 3:48 am

I’m a newcomer to digital photography so this is probably a really dumb question.

But here goes anyway.

When I look at the “properties” of a digital photo in Windows picture viewer it gives one figure, eg 2.2MB, but when opened in photoshop it gives a much much bigger figure.

Why is that?

Kind regards.
Murray Hunter says:

February 18, 2007 at 10:48 am

If I downsize picture & increase p.p.i then resize & decrease p.p.i back to original will the quality be the same ?
Murray
Mike Sulman says:

February 18, 2007 at 3:04 am

Blank CDs are cheap so why resize the photos to fit more on a CD?