Resizing Photos

[meobeo u]

For the record, I looked up what jpeg artifacts actually are and what causes them, and that has not helped me to answer this question. My apologies if this is a really dumb question.

Say I have a jpeg image fresh off my camera, and I want to reduce the file size so that I can upload it somewhere (including but not limited to this forum). If I open the file in MS Paint, resize it by 50% in both directions (so the image is shrunk overall by a factor of 1/4), and re-save it as a jpeg, does that cause any loss in quality OTHER than removing three-fourths of the pixels?

If yes, then how can I reduce the file size of a jpeg image without corrupting it (beyond the obviously-unavoidable reduction in resolution)? Do I just need to be using more sophisticated software than Paint? I obviously don't intend to use Paint for any "real" photo editing; I'm just wondering whether using something else is necessary for this particular problem. The Windows 10 "Photos" app appears to be able to crop a jpeg without introducing artifacts (thank goodness), but it doesn't resize.

If no (or perhaps "no you idiot, why would you even think that"), then what kind of editing and re-saving does introduce jpeg artifacts? I've always avoided them simply by saving edited images in any format other than jpeg - even if the image was a jpeg to begin with - usually png; but that doesn't work when resizing an image to reduce the file size, since png has a higher data density than jpeg.
Lee!

 

[D7K]

In MS Paint - I believe you can just use the resize option, check the maintain aspect ratio box and enter the pixels you want for say the longest side... for web maybe 1000/1200 for use on this site for example, as you've checked maintain aspect ratio it will automatically fill the height pixels and you're done... I find it easier to determine what is the max pixel size for the site you want to upload to and use that. If it's a portrait image then just enter the maximum height in pixels that the site allows and again the width will auto-fill as you've selected maintain aspect ratio...

 

[Ysarex]

For the record, I looked up what jpeg artifacts actually are and what causes them, and that has not helped me to answer this question. My apologies if this is a really dumb question.

Say I have a jpeg image fresh off my camera, and I want to reduce the file size so that I can upload it somewhere (including but not limited to this forum). If I open the file in MS Paint, resize it by 50% in both directions (so the image is shrunk overall by a factor of 1/4), and re-save it as a jpeg, does that cause any loss in quality OTHER than removing three-fourths of the pixels?

Yes. The original JPEG compression grid embedded in the photo will interact negatively with the resampling process.

If yes, then how can I reduce the file size of a jpeg image without corrupting it (beyond the obviously-unavoidable reduction in resolution)?

You can't. That's what it means to be JPEG.

Do I just need to be using more sophisticated software than Paint?

A different resampling algorithm (Photoshop offers 6 for example) may help but there is no damage free option only less damage versus worse damage.

I obviously don't intend to use Paint for any "real" photo editing; I'm just wondering whether using something else is necessary for this particular problem. The Windows 10 "Photos" app appears to be able to crop a jpeg without introducing artifacts (thank goodness), but it doesn't resize.

Right, cropping is not a problem.

If no (or perhaps "no you idiot, why would you even think that"), then what kind of editing and re-saving does introduce jpeg artifacts?

Everything except cropping. There's a reason that the creators of the JPEG algorithm describe the file format as an "archive format." Once it's done anything that alters pixels in the image will cause a negative interaction with the embedded compression grid. What folks have discovered, especially in recent years with higher resolution cameras is that the convenience of working with JPEGs outweighs some minor damage that's probably not visible.

Joe

I've always avoided them simply by saving edited images in any format other than jpeg - even if the image was a jpeg to begin with - usually png; but that doesn't work when resizing an image to reduce the file size, since png has a higher data density than jpeg.
Lee!

 

[RVT1K]

What about saving a copy of the file as a bitmap and resizing the bitmap?
Is there still loss?

 

[Ysarex]

What about saving a copy of the file as a bitmap and resizing the bitmap?
Is there still loss?

Yes.

Joe

 

[otherprof]

For the record, I looked up what jpeg artifacts actually are and what causes them, and that has not helped me to answer this question. My apologies if this is a really dumb question.

Say I have a jpeg image fresh off my camera, and I want to reduce the file size so that I can upload it somewhere (including but not limited to this forum). If I open the file in MS Paint, resize it by 50% in both directions (so the image is shrunk overall by a factor of 1/4), and re-save it as a jpeg, does that cause any loss in quality OTHER than removing three-fourths of the pixels?

If yes, then how can I reduce the file size of a jpeg image without corrupting it (beyond the obviously-unavoidable reduction in resolution)? Do I just need to be using more sophisticated software than Paint? I obviously don't intend to use Paint for any "real" photo editing; I'm just wondering whether using something else is necessary for this particular problem. The Windows 10 "Photos" app appears to be able to crop a jpeg without introducing artifacts (thank goodness), but it doesn't resize.

If no (or perhaps "no you idiot, why would you even think that"), then what kind of editing and re-saving does introduce jpeg artifacts? I've always avoided them simply by saving edited images in any format other than jpeg - even if the image was a jpeg to begin with - usually png; but that doesn't work when resizing an image to reduce the file size, since png has a higher data density than jpeg.
Lee!

I solved the resizing for the Forum problem by sending myself an e-mail of the photo - choosing “large” in the e-mail option, opening the e-mail and using a two-finger tap on the image and choosing “send to photos” from the menu that opens up. The resized image shows up in “imported” in Photos.

 

[jcdeboever]

I use GIMP for posting images into social media. Image>rescale>make image 1024 or 2048 on long side and hit chain link to settle the short side> file>export>jpeg at 100% quality.

I use this open software program for most of my editing. I am not into editing so I do very little tweaking with my images. Maybe some curve adjustments, clone tool, etc.

 

[dennybeall]

My suggestion is to download the image to your PC and save it, preferably save the original. If you need a copy for something then load the original into your software make the changes and do a "Save As" with a code word added to the file name, such as "-SMALL". The files are easily recognized and you can just delete the "-SMALL" identified copy later.
I use Bridge and Photoshop so am not familiar with the other programs mentioned.

 

[WayneF]

Say I have a jpeg image fresh off my camera, and I want to reduce the file size so that I can upload it somewhere (including but not limited to this forum). If I open the file in MS Paint, resize it by 50% in both directions (so the image is shrunk overall by a factor of 1/4), and re-save it as a jpeg, does that cause any loss in quality OTHER than removing three-fourths of the pixels?

If yes, then how can I reduce the file size of a jpeg image without corrupting it (beyond the obviously-unavoidable reduction in resolution)? Do I just need to be using more sophisticated software than Paint? I obviously don't intend to use Paint for any "real" photo editing; I'm just wondering whether using something else is necessary for this particular problem. The Windows 10 "Photos" app appears to be able to crop a jpeg without introducing artifacts (thank goodness), but it doesn't resize.

Resampling smaller does give up lots of pixels, but that is of course the exact result that you seek.

Any change also involves another final SAVE as JPG again, which is yet another JPG compression operation, and another addition of JPG artifacts. Unavoidable though, in that case. So select a reasonably high JPG Quality setting when you do it (Not maximum, but up towards it, maybe at least 8 of 10), and only do it once if possible. Meaning, if later discovering you need a redo of this, and if possible in the situation, do NOT "redo again" (adding yet another JPG compression), but instead, delete the previous result, and do it again from the original, which is then a first repetition again.

There are different methods of resampling, of varying image quality (called Nearest Neighbor, Bilinear, Bicubic, etc). In the early days, resample of millions of pixels was a heavy job for the then slow computers, and the faster simpler methods were used back then, but computers easily handle better methods today. I have no idea how MS Paint does it, but it is an extremely old program, and it is only just a simple drawing program for graphics, definitely NOT a photo program. I would seek others instead. A free and popular one that is simple, easy, and good is Irfanview (just search Google). It is a very good photo VIEWER, not a full editor, but also does resample very well.