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Posted on 23/11/11 4:12:19 PM |
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Deborah Morley
Makeover Magician Posts: 1319 Reply  |
Two dumb questions
First dumb question; (Using a Mac) if I click on an image and go to File>Get Info I will get a size of 3.3mb, however when I open in Photoshop it will say the size is 28mb. Which is the 'true size'? And why such a big difference? Second dumb question; yesterday I was helping a neighbour resize some images to send off for a competition, this I was doing in Photoshop as I couldn't work out how else to do it. The images were about 68cm x whatever but at 72dpi. So I altered to 300dpi and took the size down to approx 600pixel long to abide by the rules. In Photoshop this meant the images were approx 1mb each. However, when I emailed them they were a lot smaller. Is there a way to resize, and set the dpi without using photoshop; rather than just saying small medium or large image as iPhoto does? |
Posted on 24/11/11 07:48:28 AM |
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Steve Caplin
Administrator Posts: 7025 Reply  |
Re: Two dumb questions
Not dumb questions at all, Deborah! 1. The size of 3.3Mb is the size of the jpeg file. It's a very compact file format, greatly reducing the size of the file while causing only minimal damage to the image (jpeg is a "lossy" file format). When you open the file in Photoshop, the size you're seeing is the size in terms of the sheer dimensions of the image, according to the pixel count. If you saved that file as a .psd, then doing Get Info on it will show it to be very similar to the 28Mb you see in Photoshop. 2. Photoshop is by far the best way to resize images. Each image has three dimensions: the height, the width, and the dpi (actually, in computer terms it's the number of pixels per inch, not dots - pip; dpi is the printing equivalent). So if an image is 1 inch square at 72 ppi, it contains 72 x 72 = 5184 pixels. If the images is 1 inch square at 300 ppi, it contains 300 x 300 = 90000 pixels. When resizing an image, if it's for top-quality print you should save it at 300 ppi; if it's for on-screen display, at 72 ppi. You can change the resolution in Photoshop without changing the number of pixels, by unchecking the Resample Image button in the Image Size dialog. This will leave the pixel count alone, and the new width and height will be shown instead. I'm curious as to why you were reducing the ppi, and then reducing the pixel count. What were you trying to achieve? Did you need to get the image below a specific file size? If you need to get an image down to a specific size in Mb or Kb, one way to do it is to use Save for Web. This allows you to set the image dimensions as well as the quality of the jpeg - but it will change the resolution to 72 ppi. Alternatively, you can keep the image at 300 ppi, and guess at the dimensions. Then, in the Save dialog, you'll be given an idea of how big the file will be for each jpeg quality setting. It's a bit convoluted, but probably the better solution. |
Posted on 24/11/11 09:21:13 AM |
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Deborah Morley
Makeover Magician Posts: 1319 Reply |
Re: Two dumb questions
Thanks for that Steve, after all these years of using Save for Web, have never really taken in that a JPEG is such a different format from PSD! The file sizes had to be below 1MB, but also no more than 600pixels along the longest side, which was really dumb. Also the images were going to be projected on a wall to view them!, which was why I was saving them at 300 (Talk about confusing). I will now have a play around to work out to try and work out if an image is 1MB in JPEG form what it will be in photoshop. So one more question; as I may have more of these to do, what would be the best way to Automate? Do I make a droplet? Sorry to ask such a basic question, I really must learn some of the other side of photoshop. |
Posted on 24/11/11 3:06:53 PM |
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Steve Caplin
Administrator Posts: 7025 Reply |
Re: Two dumb questions
The 600 pixel dimension makes sense - but no point saving them at 300ppi! Best to stick to 72, since they’re going to be projected. Setting up an Action is the best solution here. You should use the Fit Image command (under File > Automate) to set the 600 pixel limit. And at 600 pixels they're guaranteed to be well under 1Mb, so no need to worry about that at all. |
Posted on 24/11/11 6:41:43 PM |
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Deborah Morley
Makeover Magician Posts: 1319 Reply |
Re: Two dumb questions
Thanks for that. I called in at the Apple store today and discovered that in Preview you can change the dimensions and the ppi. Don't know how much difference there would be in the final image as opposed to doing it in photoshop. Will have a play. |
Posted on 24/11/11 7:38:05 PM |
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Steve Caplin
Administrator Posts: 7025 Reply |
Re: Two dumb questions
You can do it in Preview, of course, but that's a workaround for people who don't have Photoshop! |