This post covers some recent experiments I have done with JPG saving of images where I would like some feedback from others who have also done experiments.
I am not after comment from arm-chair experts quoting magazines, other internet sites or third-hand pronouncements from other sources
I guess that I, like you, have read & been told "don't use JPG, you'll lose too much image quality" ...
I have also read photo magazine articles "claiming & showing test images" that purport to show that JPG images go fuzzy from pixellation if you save a JPG to another JPG - so I decided to try a number of things and see where it got me
Firstly I took a 12mpx [4000 x 3000px] ex-camera jpg image as my 'base-line' image
a) I opened the image [original]
b) then cropped the image to a smaller size
c) then chose 'undo' to return it back to its former size
d) then saved the ex-camera image as JPG > JPG with PS Quality=12/12, & renamed the file as 'image-1'
ie- no real & lasting change to the image occurred, but it was saved JPG > JPG
This was repeated 4 times with image-1 being opened, altered, undone, then saved as image-2; then repeated image-2 to image-3; image-3 to image-4 etc.
The 1st result was- the ex-camera JPG image is 6,2Mb in size, the image-1 -2 -3 -4 & -5 saved images are all 6,1Mb in size and all still 4000 x 3000px in size
Experiment result- no loss of image size either via pixel dimensions or file size
I repeated experiment-1 with a 3mpx [2048 x 1536px] image and using a Win-95 version of Photo Express software [rather than PSE]. The ex-camera image was 1.04Mb in size, ALL the saved images were all 660kb in size when using the default JPG > JPG saving regime
result- again no loss of image size either via pixel dimensions or file size beyond the initial JPG > JPG save
Involved printing the image(s) - I wanted to see what visible changes occurred via JPG > JPG saving of the image
I then saved the 12mpx image [from experiment-1] with JPG > JPG format and set PSE Image Quality as 12/12, then 9/12, then 6/12, then 3/12 and finally 1/12. To ensure no mixups occurred during printing, a small text comment was inserted into each image via a text layer then flattened before saving & printing
I then took the above 12mpx ex-camera jpg image & all the saved copies down to my local print shop. Each was printed as 12" x 8" prints
So with a series of 6x 12" x 8" prints on the table, I sought the comment from the local photo-professional as to each image
He was unable to see any visible difference between any of the 12" x 8" prints - and expressed amazement that the details in the PSE 1/12 quality image was just as as the 12/12 quality image. [the image subject was my missus, and we were looking at the weave of her dress fabric along with fine-ness of her hair] He did locate a very slight colour-shift in one small portion of the image, but stated that "without the original to compare it with, he would not have noticed anything"
Overall he was astonished and could not answer the basic Question - why is there so little IQ difference between PSE quality 12/12 versus 1/12
Attached here is a 1024px image showing a portion of the image from experiment-3, where a new canvas of 4000px wide was prepared and partial images from the experiment-1 images were pasted and some text added. This image has been reduced to <250kb for posting here and you can see the resulting "loss" of from repeated JPG saves
So - over to you ... what's going on? ... why do we keep getting told that "JPG > JPG saves will cripple our images?" when quite obviously from the above it does nothing of the sort