A recent conversation at a local art group turned on the question of whether GIMP (https://www.gimp.org) - the “open source” image editor - would be an acceptable substitute for Photoshop.
Adobe, Photoshop’s creators, now have a subscription business model, which means you pay a monthly fee to license a selected package of their image management tools, usually with a certain amount of “cloud” storage so you can access your work from any computer, and edit over the web. I take quite a lot of photographs, but I only need the power of something like Photoshop at most once or twice a week, and on that basis the cost-per-frame handled would typically work out at £1-£2, and it makes me think that I could be satisfied with a tool almost as powerful even if it did not have the same professional polish.
Of course, if you are earning a living that involves regular and sophisticated image processing, or even if you are a very keen amateur photographer processing thousands of images each year, you may well consider that a reliable regularly updated professional suite of well integrated, well documented and easy-to-use software tools is well worth the monthly licence fee. Most professionals would see it as a reasonable business overhead and the keen amateur spending thousands of pounds on kit may believe that he will not get the best from his high-end cameras without high-end post-processing. If money is no object, Adobe’s “industry-standard” Creative Suite is a safe option, but if like me you know that you are unlikely to use more than a small fraction of its capability, and then only infrequently, you may well look around for alternatives that will provide the functionality you require at lower or even no cost - even if it involves some minor inconvenience.
The nearest equivalent to Photoshop is indeed GIMP, which is freely downloadable, and runs on just about any computer you are likely to find around at present. Furthermore, unless you have particularly demanding requirements it will almost certainly provide most the capabilities that you might need, and for most people a good deal more than they actually need. One of the major reasons that professionals could not live with GIMP, however, is its limited capability with handling different colour spaces: professionals are focussed on producing client products that usually involve printed material, and need absolute certainty that what they see on the screen will be exactly reproduced by the inks of high-end commercial printers.
Photoshop or GIMP may not, however, be what you actually need. If you take more than a few casual photographs (or, for example, you accumulate images a reference material for art work and need to find saved material easily) you may be better suited by a “digital asset management” product, which also provides a range of editing tools. I shall therefore take a look at Digikam (also open source, https://www.digikam.org) which is roughly equivalent to Lightroom, Adobe’s “Creative Asset Management” tool. Digikam maintains a database which allows you to associate descriptive tags with images, and group them into collections in a variety of ways. It also provide an adequate image editor that covers at leat 95% of my photo manipulation needs. I have installed it on my Windows laptop, along with GIMP for the small amount of work that Digikam does not cover. There are, however, other open source products available, and which you choose is a matter of taste and, to some extent, the one you have invested a little time learning to use.
Since GIMP and Digikam are free, there must be some downside, or everyone would be using them. That is certainly the case, but it comes down to a cost vs convenience balance that is essentially a matter of personal choice, taste and experience. The following comments are directed towards GIMP, but most of them also apply to Digikam.
Firstly, GIMP is not Photoshop. If you have already learned the Photoshop/Adobe way of doing things (and low-cost educational licences mean that it is often taught in schools and colleges) there will need to be a bit of re-learning. GIMP’s volunteer community of developers could not copy the Photoshop style without infringing copyright - and maybe they even thought that they could do better (because they do include some very talented designers). Nevertheless, Adobe has been able to spend large amounts of money in polishing Photoshop to a high professional gloss. Nevertheless, I think that the common tasks in GIMP are usually pretty straightforward. Ultimately, a wider range of functionality will be available to you within Photoshop, and in some respects it will probably be easier to use, but will you use it? On the other hand, the greater range of functionality may carry its own disadvantages: there is simply more to learn and more than you can misunderstand and get wrong.
Secondly, the GIMP documentation is not nearly as good as Photoshop. It is not bad, in fact some of the tutorials are very useful. Nevertheless, I think that it lacks the polish that comes when you hire (at considerable expense) top-class professional documentation authors. Furthermore, some of the material is not completely consistent with the latest version of the GIMP user interface (though the principles remain clear, and I had no trouble following the lesson). The bottom line is that it would probably take you longer with GIMP than with Photoshop to work out how to accomplish for the first time some complex multi-step image processing task. (I have occasionally used a secondhand Photoshop “cookbook” which maps out the logical sequence of steps one needs to go through in order to get a particularly complex effect, and just converted it function-to-function to the GIMP equivalent.) I am, however, perhaps not the best judge in this area, because I have spend 40 years building, documenting and using complex software, so I have more than average ability to think my way into the heads of other software designers.
Thirdly, GIMP is not seamlessly integrated with the other tools that are required by those who work with large collection of images. Professional photographers and graphic artists have high rates of image throughput, and need reliable tools to manage libraries of many tens of thousands to hundreds of thousands of images. They also want to toss images between different tools with the minimum of effort. If you are dealing with the products of a photoshoot comprising hundreds of images, a few extra seconds handling each frame quickly adds up to extra hours. I am not by any means the most active of amateur photographers, but my library grows by several thousand images each year. Without a systematic approach to digital asset management I could easily loose useful material in the general photographic noise.
Many of the comments I made about GIMP, in term of polish and documentation, apply to Digikam, but it certainly seems to do an adequate job once you have adjusted to its world-view. There will always be a learning curve and a certain amount of pain associated with moving from an “industry-standard” product, but there is a magic key to learning that never fails: read the manual! As a software developer of wide experience, who has studied user interface design at Masters level, read many books on the topic and even sat on international committees dealing with man-machine interface issues, I am well aware that almost no one ever reads the manual until they have tried everything else. Most people want others do their learning and thinking for them if at all possible and like to follow simple recipes without understanding principles. The route to open source, however, tends to be less painful if you accept that most answers are in the manual and a modest learning effort will replay high dividends.
I believe that if you have a sufficiently large collection of images such that a certain amount of curation and cataloguing would be sensible, Digikam may well do all that you need, including the most common image editing tasks. The most useful additional functionality in Photoshop or GIMP is centred around “Layers” which allow you to build up images from stack of image components, of varying opacity and content. If you are not prepared to learn how to use Layers, or do not need to undertake the tasks they enable, you loose half the point in using either Photoshop or GIMP in preference to Lightroom or something like Digikam. Admittedly both Photoshop and GIMP have extensive sets of “Filters” for special effects and also allow “plugins”, which are functionality extensions that can be provided by 3rd parties (you can write them yourself if you are prepared to learn the tricks). Photoshop inevitably has a wider range of filters and plugins available for specialists tasks - but you may have to pay for them. Whether you think that these actually enhance your images is a matter of taste. I rarely employ any of them.
There are many other image management tools available, often well recommended by users on the web, some free, some low-cost. I did a survey of reviews and eventually choose to try Digikam. It seemed to be good enough for my needs (especially since it is not my primary asset management tool) so I have not tried to install and use any of the others. I am therefore not in a position to give my own survey recommendations.
Although I have installed Digikam and GIMP on my Windows laptop, I also use an Apple Mac desktop. (There are reasons why a lot of creatives like working with Apple’s hardware and software, but that is another story.) MacOS has its own integrated “Photos” application, providing fairly intuitive asset management and basic editing (cropping, colour balance, exposure adjustment etc) - roughly functionally equivalent to Lightroom or Digikam though perhaps less comprehensive. That is what I use most of the time, and I can also call up GIMP (from within Apple Photos) when I want something with more power. My style of photography does not depend on heavy image manipulation, so Apple’s Photos does almost all that I need. (The exception is with monochrome images where I like to do some of the “dodge-and-burn” and contrast manipulations that I used to do in a darkroom.) In practice, GIMP is fired-up for only a few percent of the frames I want to keep. The Photos/GIMP combination would, however, not do the trick if my library were significantly larger, or if I had professional customers, but at present it floats my boat.
A potential problem with Apple Photos, and potentially with other photo management applications, is a certain amount of lock-in: image asset management involves adding a lot of “meta-data” to frames which the software typically store in a proprietary database that is separate from the image file itself. Having invested a great deal of time in adding important descriptive and tagging information, you do not want to risk loosing it should the software become obsolete. (This happens: Google encouraged many people - including me - to adopt their Picasa web-based image management system some years ago, and which I found entirely adequate. Then they made a strategic change of direction and withdrew, leaving users with the job of migrating as best they could to other systems.) I know, however, that there are routes out of Apple Photos and Digikam that I can use if necessary. (Both of these products can actually access the Apple Photos image database and Digikam will also export its database contents in a format accepted by many other image management applications. ) There are also softer forms of lock-in: once you have learned to use a complex toolset you simply do not want to change and you have probably stored a large amount of digital information in a tool-specific format. Even if migration routes exist, you probably do not want to contemplate the effort involved. Hence, if Adobe increase their subscription prices, most users simply have to grin and bear it. There is no realistic alternative in you are a professional or have a large digital investment based around Adobe software.