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FORUMS Post Processing, Marketing & Presenting Photos RAW, Post Processing & Printing
Thread started 24 Dec 2017 (Sunday) 11:17
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Does reducing a jpg soften it?

 
OhLook
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Dec 27, 2017 00:01 as a reply to post 18526892 |  #46

I don't see a difference, either, but I also have a 15" screen.

For another comparison, the same reduced by 75% in Preview:

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And can someone tell me how to find the amount of compression?

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Pippan
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Post has been edited 26 days ago by Pippan.
Dec 27, 2017 00:12 as a reply to post 18526876 |  #47

To my eyes and on a 5K iMac screen, the AMASS reduced version looks slightly sharper and more detailed. Nevertheless I think it's time I started using the CS5 Photoshop I've had on my computer for years and been too over-awed to try.

I didn't realise you did all (or nearly) your edits in Preview. I actually do the raw conversion and global adjustments with Photo Ninja and just use Preview to resize because PN doesn't give you the option of specifying pixel dimensions when converting to jpeg. PN is a good program otherwise though and I can use it as a Photoshop plugin, so I will. I understand doing a final sharpen at output size, which you can do with Photoshop, makes a big difference.




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Lyn2011
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Dec 27, 2017 03:02 |  #48

And can someone tell me how to find the amount of compression?

Do you have Photoshop Elements? In File > Save for Web, you can see before and after resizing. Mostly I use this program for to resize for internet, but Canon's DPP can resize too: in File > Convert and save you can resize very well, although you can't see how big (MB's) the photo will be.




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tzalman
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Dec 27, 2017 03:49 as a reply to OhLook's post |  #49

And can someone tell me how to find the amount of compression?


In general, when photographers who aren’t complete nerds (like me) talk about jpg compression, they are referring to it in an imprecise way as being “high” or “low” because the photo editing programs they use have an interface that while giving them a choice of “Quality” settings, represent the amount of compression being applied only indirectly. The amount of compression is inverse to the “Quality” – a high Quality setting uses less compression and a low Quality setting uses more compression in order to achieve a smaller file size while sacrificing quality. And different programs use different “Quality” scales; Photoshop uses 0 – 12 while Lightroom uses the same 13 Adobe compression algorithms but they are represented by a crazy 0 – 100 scale. DPP uses 1 – 10. (I don’t know Preview, but I wouldn’t touch any program that doesn’t give the user some control over jpg quality vs. compression.)

The subject is further complicated by the fact that the amount of compression done at a given setting is also influenced by the photo’s content. Large areas of solid or near solid color, like blue skies, compress well, but highly detailed photos and highly sharpened images are less amenable to compression. Also, image noise cannot be differentiated from image detail, so in general, as ISO goes up, compression goes down and file size increases.

To really know, in hard numbers, the amount of compression that has been done to a given jpg photo file, you have to know its uncompressed size. There is a simple formula for that: [Pixels X 3] / 1.048 = MB. The explanation: Pixels is the total number of pixels in the image, height times width. Each of those pixels contains three color values (Red, Green, Blue) and in jpgs those values are always written in 8 bits. 8 bits equal 1 byte, so each of the three color values equals 1 byte of data. Pixels times 3 gives the total image content in bytes. 1024 bytes are a kilobyte and 1024 kilobytes are a megabyte (MB), so dividing twice by 1.024 or once by 1.024 squared (1.048576) gives the answer in MB.

Dividing the uncompressed size by the jpg size, gives the amount of compression.

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Levina ­ de ­ Ruijter
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Dec 27, 2017 09:50 |  #50

OhLook, I took your two 1280px versions to Photoshop and blew them up to have a better look. The AMASS version clearly has the edge. But the Preview version after some sharpening is right up there. Here is the comparison. Blown up to 500%. Left the Preview version, in the middle the AMASS version, right the Preview version after some sharpening.

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digital ­ paradise
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Dec 27, 2017 09:58 |  #51

Like many have said never let a website resize your images. Upload to the size you want to display. Learn about the 3 phases of sharpening.

https://www.cambridgei​ncolour.com ...ials/image-sharpening.htm (external link)

Do capture and creative sharpening at 100%. Do your final or export sharpening after resizing to the size you plan to upload.

The resampling algorithms have improved a lot over the years but there are different ones. I don't know what preview uses.

You don't own PS but this may help explain some things. In the resizing video it talks a lot about upsizing and for print but some good info. Other software works the similar way.

https://www.youtube.co​m ...4mV3NsLmXw&feature=​relmfu (external link)

https://www.youtube.co​m ...ure=player_embedded​#at=20 (external link)

I really like pushing crops to the max and resizing. Being careful and following a few key steps makes a big difference. Second image is a crop.

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digital ­ paradise
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Dec 27, 2017 10:00 |  #52

PPI has no effect on screen viewing. 1st image is set to 1. Next image 1000

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digital ­ paradise
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Dec 27, 2017 10:41 |  #53

Have you tried using Canon's DPP? I found the resizing algorithms have improved over the years. I think the sharpening on the basic image adjustment window defaults to 3 which is pretty good. Try 4 and it starts to get aggressive at 5. The File - Convert and Save command offers pixel dimensions.


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John ­ Sheehy
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Dec 27, 2017 10:50 |  #54

digital paradise wrote in post #18527185 (external link)
PPI has no effect on screen viewing. 1st image is set to 1. Next image 1000


thumbnailHosted photo: posted by digital paradise in
./showthread.php?p=185​27185&i=i253720085
forum: RAW, Post Processing & Printing
thumbnailHosted photo: posted by digital paradise in
./showthread.php?p=185​27185&i=i122056249
forum: RAW, Post Processing & Printing

Good thing the first one doesn't automatically print for you when you look at the post.

That's a lot of paper and ink.




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Dec 27, 2017 11:11 |  #55

digital paradise wrote in post #18527181 (external link)
thumbnailHosted photo: posted by digital paradise in
./showthread.php?p=185​27181&i=i115440898
forum: RAW, Post Processing & Printing
thumbnailHosted photo: posted by digital paradise in
./showthread.php?p=185​27181&i=i63303048
forum: RAW, Post Processing & Printing

Interesting that the crop looks sharper & with more detail than the original image.


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digital ­ paradise
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Dec 27, 2017 11:26 |  #56

PhotosGuy wrote in post #18527221 (external link)
Interesting that the crop looks sharper & with more detail than the original image.

No PP with the original.


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John ­ Sheehy
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Dec 27, 2017 13:41 |  #57

PhotosGuy wrote in post #18527221 (external link)
Interesting that the crop looks sharper & with more detail than the original image.

That's pretty common when the downsampling method does not include a lot of sharpening. A downsample can be all over the map, sharpness-wise, with the same original image. Upsampled images, too, can have ramped or splined transients between original pixels, or just duplicate them and maintain pixel contrast.




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Pekka
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Dec 27, 2017 14:16 |  #58

Some comments on this:

- always store original (RAW) locally in at least three storage mediums! That is your (pre-)negative, your most valuable possession.

- To make life easy, trust AMASS to resize your uploaded photos, just make sure you upload something like 3-5MB size (2500x2500 or so). If you upload in 1280 size, it won't be sharpened or resized here, but it is re-saved (JPEG compression artifacts accumulate). Uploaded originals won't be stored on the server after resize is done. Don't worry about server stress, just do it.

- Next version of the forums will have a 1600x1600 upload choice, and sharpening (USM) strength selection (easy to change for each upload). You can also choose to apply sharpening on downsize only, or also to sizes that already fit to rules. JPEG compression quality will be improved in AMASS 2.0, too.


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digital ­ paradise
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Dec 27, 2017 15:56 |  #59

John Sheehy wrote in post #18527342 (external link)
That's pretty common when the downsampling method does not include a lot of sharpening. A downsample can be all over the map, sharpness-wise, with the same original image. Upsampled images, too, can have ramped or splined transients between original pixels, or just duplicate them and maintain pixel contrast.

True and the algorithms have really improved over the last 10 years.


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Does reducing a jpg soften it?
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