Does reducing a jpg soften it?

Levina de Ruijter wrote in post #18525951
1. Because you don't want large, high res files on the internet where everyone can grab them

People that steal images don't give a damn about resolution. In fact, I doubt they even know what it means.

They see a 'pretty picture' and it's 'on the internet'......therefo​re, it's free for the taking.

saea501 wrote in post #18525937
Why are you resizing your images at all?

• So it takes less time for you and I to download images to the server
  
• so it takes less time for the server to upload images to POTN readers for better response when using wireless devices
  
• so it all reduces the bandwidth consumed by data going back and forth from the millions of internet bandwidth users, so that we are not waiting for bandwidth availability
  

Enjoy your resizing.

saea501 wrote in post #18525957
Enjoy your resizing.

Even in this thread it has been shown that allowing the resizing to happen automatically outside of ones control provides lower quality images. I have seen it time and time again on many platforms ... not optimizing before uploading will almost always give inferior results. If you don't care about that, fine.

Enjoy your soft images.

I want to determine myself how my image will look online, so I make it the size that will be displayed "as is".

Do my images look soft to you?

Levina de Ruijter wrote in post #18525927
OhLook, you have blown up a small, downsized image to match the dimensions of the high res file. Of course the result will result in a heavily pixelated image! You're comparing apples to oranges here.

There was a reason. I wanted to know whether that amount of distortion was a normal and expectable effect of reducing a jpg. Dave's experiment showed that it is not. Conclusion: Preview is a lousy way to resize.

Unfortunately, with what I have now, the reverse is true. AMASS does a better job than Preview at resizing.

saea501 wrote in post #18525937
Why are you resizing your images at all?

For the following reasons that others gave:

Levina de Ruijter wrote in post #18525951
2. Because forums such as POTN have limits

Wilt wrote in post #18525956

• So it takes less time for you and I to download images to the server
  
• so it takes less time for the server to upload images to POTN readers for better response when using wireless devices
  
• so it all reduces the bandwidth consumed by data going back and forth from the millions of internet bandwidth users . . .
  

agedbriar wrote in post #18525999
I want to determine myself how my image will look online, so I make it the size that will be displayed "as is".

And because large files take longer to copy and use more disk space where originally stored and in backups. The esthetic end of photography appeals to me. Fussing with technology doesn't. Waiting for something to upload or download or cross-load (?) ranks with listening to repetitions of "Your call is important to us. Please stay on the line . . ."

Anyway, I can't see a whole full-size image at once on my laptop screen for editing. The laptop that this one replaced was even smaller.

OhLook wrote in post #18526056
There was a reason. I wanted to know whether that amount of distortion was a normal and expectable effect of reducing a jpg. Dave's experiment showed that it is not. Conclusion: Preview is a lousy way to resize.

The point is you don't know what the amount of distortion is because you don't know how to compare the files properly.

I just did a few tests and I don't see much difference. Neither Preview or AMASS do very well. But I think Preview has the edge here if alone because you can control the final output better. Just make sure that after downsizing in Preview you apply another round of sharpening!

You can edit your images at any size. But noise reduction and sharpening should be applied at 100% zoomed in. If not, you won't be able to see the effect properly. Just zoom in to a 100% with the main subject visible on the screen before applying noise reduction/sharpening.

OhLook wrote in post #18526056
Conclusion: Preview is a lousy way to resize.

JPG image quality depends on two things. The number of pixels in the image and the compression applied when creating the JPG. Even a larger file with lots of pixels will look bad if too much compression is used. You need to check the settings of the software to see what sort of compression is being applied.

Why would you back up the files you produce for posting to the web? They are disposable. You back up the original file (at full size) in case you need to produce a new, resized JPEG for posting again.

Dan Marchant wrote in post #18526240
Even a larger file with lots of pixels will look bad if too much compression is used. You need to check the settings of the software to see what sort of compression is being applied.

I don't know where to look to find out the compression.

The version I post is the one I've edited to look the way I want: doing any color correction and so forth. Discarding it would mean starting over, duplicating the work, if I were to need another copy.

OhLook wrote in post #18526248
I don't know where to look to find out the compression.
The version I post is the one I've edited to look the way I want: doing any color correction and so forth. Discarding it would mean starting over, duplicating the work, if I were to need another copy.

You do all your edits at full size and save. Then you resize that finalized version and save it under a slightly differerent file name. This one is disposable after uploading.
The first one is still there.

really you should be archiving the original unedited file. That's quite easy if you shoot RAW, since all you have to do then is keep the RAW file. All RAW editing systems are parametric, which means that edits are saved as a list of instructions to the software on what settings to apply when the image is converted to pixels. Most systems use a simple list in plain text to achieve this.

Even if you don't shoot RAW you should keep a copy of the original file, as it came straight out of the camera. This ensures that if for any reason you screw everything up editing wise, you have the original image to start over with.

Editing should where possible always take place on a full resolution copy of the image, at the highest quality settings. I would also advise that you should never crop this master image. By not cropping at this stage you allow options for later, you might not want to print the image at the moment, so you crop it for viewing on screen at some random aspect ratio. Later you might need to print it at say 10×8, starting with all of the pixels can make the difference between making a useable crop, or not being able to make a print at all at that size.

This copy should also be archived so that you have access to the best possible copy of the edited image, so that you have those choices for how you can use it in the future. Otherwise somebody might have to spend a lot of time fixing things for you later.

As a case in point, I had to spend several hours removing JPEG artifacts by hand from an image, the only copy of which was an approx 500px square, highly compressed version downloaded from Facebook. My daughter wanted me to make a print of it as a christmas present for her to give to her boyfriend. It was the last photo taken of him and his grandfather. I managed to make an 8" square canvas print from it, that was great to look at for a non photographer, for whom content trumped quality. My life would have been so much easier if I had been able to start with the original file that came out of the phone.

Only once you have finished the editing of the master copy should you resize the image ready for its intended use. The resizing process should also include the crop for output aspect ratio as well as steps to ensure that an appropriate level of image sharpening has been applied after you resample the image. I say appropriate for the use, since the amount of sharpening for making a print will be significantly different to that required for onscreen viewing. This last image would be the only one that I didn't archive. I would just use it, i.e. print it, or upload it to wherever, then delete the file from my local system. The software that I use does make this final stage very easy for me though, as Adobe Lightroom has really good export systems, it is most definitely not just a RAW converter.

Alan

There is nothing mysterious with reducing pixel count by 75% and losing sharpness due to that alone, and it has NOTHING to do with editing JPG files, per se. It even happens when you take a RAW file and reduce its pixel count by 75% !

I just shot a photo of an 18" metal ruler, spanning the horizontal dimentions of a 7DII,
and here is a crop taken from that shot, output as a JPG at original resolution (5742 x 3648) and then a crop taken of the resulting JPG showing about 12% section of the length of the ruler

I appreciate the work that people have done to inform me and perhaps others of best practices, but it does seem that some of the advice pertains more to what the advice givers use their images for than to what I use mine for.

agedbriar wrote in post #18526299
You do all your edits at full size and save. Then you resize that finalized version and save it under a slightly differerent file name. This one is disposable after uploading.
The first one is still there.

From the camera, an image goes to ImageBrowser. I cull in IB and crop in IB if at all but do nothing else there. Cropping is much easier in IB than in Preview; I can choose an aspect ratio. Every other PP operation is easier in Preview. For one thing, an image is much larger on the Desktop, where Preview lives, than in IB. Preview also has some operations that IB lacks. IB doesn't even have sharpening.

I save the cropped image with a new name, which replaces the image number assigned in the camera, and copy it (not move it) to the Desktop. The original cropped image remains in IB. I keep the uncropped image in IB if a future need for it is remotely possible or if I didn't crop.

With Preview, I edit and resize. I do some PP in Photos if the image calls for a feature absent in Preview; most don't. After posting in the appropriate subforum, or sometimes more than one, I keep the image for use in a game in Competitions: A-Z or Colors or TPBM. Most of my contributions to those threads have appeared on POTN before. I may also want to use the image someday in a competition if it fits the theme. You can see why I don't consider an image disposable after posting it just once. The edited image is the version that gets filed in a folder and also backed up to a flash drive.

BigAl007 wrote in post #18526338
Even if you don't shoot RAW you should keep a copy of the original file, as it came straight out of the camera. This ensures that if for any reason you screw everything up editing wise, you have the original image to start over with.

Editing should where possible always take place on a full resolution copy of the image, at the highest quality settings. I would also advise that you should never crop this master image. By not cropping at this stage you allow options for later. . . . you might need to print it at say 10×8 . . .

As above, the original file stays in ImageBrowser. I don't make prints.

Wilt wrote in post #18526409
There is nothing mysterious with reducing pixel count by 75% and losing sharpness due to that alone, and it has NOTHING to do with editing JPG files, per se. It even happens when you take a RAW file and reduce its pixel count by 75% !

Even so, might different programs use different algorithms for resizing, some better and some worse, so that AMASS and Photoshop yield better reductions than Preview? Pippan's and my images come out soft on POTN when reduced in Preview. (No one else has admitted to using Preview.)

Here's a test. Original is a strip, 4000 x 800 px, from a shot of an Advent calendar, chosen because it has lots of detail.

1. Reduced to 1280 x 256 in Preview.

At those image sizes, I fail to see a clearcut advantage to one vs. the other in 'sharpness' or 'detail', but I am viewing on my 15" 1600x1200 laptop at the moment. If anything there appears to be an edge in contrast in the Preview output over the AMASS decimation.

[edit 16 hours later] Viewing on 27" 2560x1440 IPS monitor and again I see no difference between the posted images