OK, this is a VERY basic tutorial, but I've seen this handled incorrectly before, so I'm putting this here to clear things up.
You may be interested in adding a missing cover to our galleries/databases, or perhaps you want to add an advertisement scan to our gallery. Sure, you could do so by scanning your own magazine, but another option is to simply extract the image from a magazine file that has already been scanned and edited. This is how you do that.
We've got a lot of magazines available to download here, and most of them are in CBR format. CBR is essentially exactly the same as a RAR file. Likewise, CBZ is the same as a ZIP file. All of these types of files are simply containers for whatever is inside of them, in this case, the JPGs that make up the magazine scan. To access the files, all you need to do is un-rar or un-zip the file and extract the desired image(s). There's no need to rename the extension - you can open a CBR directly using Win-RAR simply by right-clicking the CBR and selecting "open with Win-RAR archiver" (or whatever program you're using.)
This is one of the reasons we prefer CBR over PDF - it allows easy access to the images inside using free programs. A PDF locks the images into a proprietary format owned by Adobe so that they can only be directly accessed if using the paid version of Adobe Acrobat which costs a minimum of $13 per month for the most basic version. Unless you happen to be an employee or stockholder of Adobe, most people would agree that having free and open access to the files is the preferable option.
But Retromags isn't the only place offering scans, and a lot of other places out there provide their mags as PDFs. So what can you do if you want to extract an image from a PDF and don't subscribe to Adobe? There are a bunch of free online programs out there that will convert PDF to JPG for you, but most of them will compress the JPG output, giving you a lower quality file than what was originally contained in the PDF. I realize that this is where I should recommend a free program for you to use, but I honestly have never found one that can extract the JPGs from a PDF without reducing their quality (including many that claim to have "lossless" extraction.) Have I mentioned that I think PDF is a horrible format for anything that is intended to be shared freely (such as our scans)? It really limits what you can do should you wish to alter or edit the files. If anyone knows of a good program for converting PDFs to JPGs, feel free to comment.
Of course, what I do to access the files is simply drop the PDF into Photoshop. Photoshop is also an Adobe product, and thus is capable of extracting the images without lowering their quality. (And of course, Photoshop ain't free, either.) However, if you happen to have Photoshop and decide to use it for this purpose, there is an important step you need to be aware of. When you drag and drop a PDF into Photoshop, you will get the following box, from which you can select the image(s) you want to extract:
By default, "pages" will be selected in the top left. YOU DO NOT WANT THIS TO BE SELECTED. Opening a file this way will change the image dimensions to whatever size is selected in the boxes on the right. In this case, it would enlarge the image to a 300ppi size, even though the actual image is smaller than that. So much like transcoding a 128kbps MP3 into a 320kbps MP3, it simply enlarges the file's size without increasing its quality (in fact, the quality is lowered.)
To accurately extract the images, YOU MUST SELECT "Images". This will open the image at exactly the same quality and size as the original image that was converted to PDF.
To be fair, it IS possible that the images in the PDF were originally the same size as the resolution selected on the right. So for example, if an image was originally 300ppi, then the image would be the same regardless of whether "Pages" or "Images" was selected. But there's no way of knowing that unless you extract it both ways and compare, so you're safer just always using "Images."
The exception to this is a "True PDF." This sort of PDF allows for images to be cut up and stored in a heavily compressed form, while keeping the text as perfectly crisp digital font. A True PDF will undoubtedly be a commercial or official release and is not something that would be created by a scanner. Trying to extract a page from a True PDF using "Images" is impossible, since a single page is often broken up into a dozen different images, each stored separately within the PDF and recompiled when opened in a PDF viewer. In this case, you would have to select "Pages" which will open all of the images that comprise a single page as one coherent image, much in the same way a PDF reader recompiles the pages. Just be aware that the size and resolution of that image as it will appear when opened in Photoshop is somewhat arbitrary and based upon whatever settings you have selected in the box on the right. As I said, the images on such pages are often very low quality, and the text is perfect quality, so there isn't actually a single "true" size or quality for a page in a True PDF (ironic, no?) Just keep in mind that since True PDFs almost always sacrifice quality for small filesizes, opening an image in "pages" with a high resolution like 300ppi selected is only going to enlarge a low resolution image, probably making it look even worse.