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I have a bunch of PNG and TIFF files—scans of old family photos and documents. I will keep them as archival masters, but for the purpose of online sharing I am creating JPEG's from these files. The simplest tool to use for it (on Mac) is Apple Preview. I wonder: is there any practical difference if I use a higher-end software instead, such as GIMP, Adobe Bridge or Photoshop? By "practical" I mean either:

  • better quality preservation in general (e.g. colour)
  • smaller files with the same level of details

Paid vs. free is irrelevant in this question. Also, I am not looking for automation, I will process them manually.

UPDATE: I realised my question is rather vague. So here is what I have in mind. When creating a zip-file, I can tell the program if I want the "fastest" or the "best" compression. These are vague terms, but the result is clear: I can get a smaller file containing the same information if I am willing to wait longer. I understand that comparing a lossy JPEG compression to lossless ZIP is unfair. But as the answer of @rafael indicates, there are quite a few parameters controlling the JPEG compression engine. I haven't dived into GIMP and PS, but at least Preview and Bridge do not provide direct control over those parameters. Which means, the software designers made some choices for me. And hence my question: is it perhaps known that PS or GIMP or Bridge do a "better" job in creating small JPEGs with visually the same quality than Preview? And also if they (being targeted towards photo professionals) are more careful with my images in terms of colours.

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2 Answers 2

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Cropping is your stumbling block. There's already a question here covering that, though - Automatic & intelligent crop 1,000 images.

Preview doesn't do profile conversion at all, which is OK if all your images are already sRGB, but bad if it isn't. You're then relying on browsers to be smart [cynical note: they're not. Safari is, but Chrome & Firefox certainly aren't.]

As for the rest, any of those apps can do the same thing; so can Apple's own Automator in one click [I have mine set as a Service, so literally a single key command from Finder], though same as Preview you don't get to choose compression quality. LemkeSoft's GraphicConverter would add scripting ability to Automator giving you that extra refinement.

'Smaller files with the same level of detail' would require you to be saving in HEIC or WebP rather than jpg - though adoption for these is not yet universal, most OSes can at least view them these days. This can also be done natively in Automator [or again GC for refinements].

For 'practical' considerations…
Anything you can do in Photoshop you can pretty much always do in Gimp, if you can stand the interface/workflow [which I can't, but others find it just fine & dandy.]
Anything you can do in Photoshop you can do slower for free in Adobe's online version, Adobe Express [needs sign-up]
Automator is free & simple, but to get real control over it you really need GraphicConverter to add the extra plugins.
Everything except Preview and 'vanilla' Automator lets you choose compression quality.
[Bridge I've never actually used.]

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  • \$\begingroup\$ Thank you for the detailed answer. I am not interested in automation, and also autocropping is irrelevant. GIMP vs PS is not critical here either (but Preview vs GIMP/PS is). However, could you please elaborate on this part of your answer: "Preview doesn't do profile conversion at all, which is OK if all your images are already sRGB"? What is profile conversion, what happens if it's not done? Will colours be distorted? What does it have to do with browsers? I am a newbie in colour management but would like to learn it. \$\endgroup\$
    – texnic
    May 4, 2023 at 18:55
  • \$\begingroup\$ An icc profile is a 'colour map' defining how colours are interpreted from an image to your screen. The web standard is sRGB. A scan may have been already converted to that, or it may still have the scanner's profile, or your own display's profile… or we don't know. In order that web browsers have the best chance of seeing the colours as intended, images should be exported as sRGB. [This is a hugely complex topic, impossible to cover comprehensively in a few pages, let alone a few sentences.] \$\endgroup\$
    – Tetsujin
    May 5, 2023 at 7:25
  • \$\begingroup\$ Personally, for my own photography, I just use two settings from Photoshop as a batch script - full size at 100% quality & 30% size at 50% quality. From a 6000x4000 27MB 'raw' file, that gives me 'archival quality' at about 14MB & 'good enough for the web' at 150KB. Viewing at full screen on a 27" 2k display, I really can't tell the difference. The difference comes when you 'pixel peep' by zooming. \$\endgroup\$
    – Tetsujin
    May 5, 2023 at 7:35
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Let me divide this into several parts.

1. JPG

JPG is a standardized file format. It has a clear specification. So what I mean, is that there is not much under the hood that "specialized" software can do to improve the quality of a JPG file that other free software can not.

But some programs give you some "default" options that compromise quality vs what people expect to have.

People expect to see a reduction of the file size and are not expected to see if the algorithm used a different quantization-sized block on the Cr channel.

My first recommendation here is that you need to understand the different variables, normally under a checkbox or slider that affect a JPG file.

Mainly, a) block size, sometimes a program says "Use a 1x1 block" or 4:4:4. b) optimization and c) color profile.

2. Before the compression

A program also can implement different resample methods (Nearest neighbor, bicubic, etc.) Additional sharpening, some micro contrast, etc. The results here are more visible, so you can experiment a bit with them on your software.

3. Smaller files with the same level of detail

You have a clear distinction between archival and presentation files, so that is a great thing.

"Smaller files" and "same level of information" (I used information and not detail) only have a threshold Is it compressed or not?

Beyond that relation is relative. Do I notice it? Is it important, for example, will the image be further edited after the compression?

Are you actively changing the real information, especially resampling it?

4. Test it

Specially Gimp. It is free and widely available, so the only thing stopping you to try is time.

5. People do not care

Some do. If you have an archival mindset, or editing mindset (like a graphic designer making a cover of a magazine). But normally people will appreciate an old grainy, out-of-focus, washed-out photo and enjoy it if it is a family member or a memory related to them.

And most probably will be further compressed when uploading it to a photo-sharing website or social media.

6. Some other formats

There are some other formats that try to overcome some real issues of JPG compression. JPG2000, WebP, and HEIF as mentioned in the other answer.

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