Image resize puzzle...

[*mark]

I’ve asked this Image Resize question before – but still making a hash of it...

Image is 3398 x 2903 x 72dpi (1196 x 1023mm) 

I want to resize it to 200 x 171mm, making it a smaller low-res image, that someone can’t simply magnify and print.

…which I can do, but when I ‘save’, the pixel measurements are virtually the same: 3386 x 2896 and AP has increased the image dpi to 413 – so instead of creating a smaller low-res image, I’m making a fractionally smaller high resolution image – the exact opposite of what I’m trying to achieve..

I’m reducing the image by 993mm, but losing just 12 pixels? I’m expecting pixellation by reducing the image size but it's as sharp as a tack – perfect for magnification and printing...

My questions are: How or why, by reducing the image size, does yet AF keep effectively making it bigger? Can someone tell me what I’m doing wrong here?? And how I make it into a smaller, low res image? Thanks

[Old Bruce]

If you are using Photo just make sure the Resample check box is ticked. 

[GripsholmLion]

3 hours ago, *mark said:

I want to resize it to 200 x 171mm, making it a smaller low-res image, that someone can’t simply magnify and print.

Apologies if my reading of this is wrong, but if you want an image which is not worth printing, I would assume that it is going to be published on the web somewhere? Yet you are resizing it using print measurements.

If it is going on the web, keep in mind that anyone who is for some reason determined enough to print a half-decent copy may get enough quality out of an AI resize and there's nothing that anyone can do about that without making images which are too poor quality to resize in the first place.

In the unlikely event that Bruce's advice does not work for you and you are still stuck, you may need to make a screengrab video of your export method and post it here.

[iconoclast]

The sizes of digital images are defined in Pixels horizontal x Pixels vertical. But Pixels themselves don't have any fixed size. For that reason you need the value in Pixel per Inch (ppi, sometimes also called "dpi" - "Dots per Inch" - which is not correct, strictly spoken). Only these ppi/dpi define the size of the image in mm, Inches or any analogue scale unit.This is called the relative resolution. This resolution has to be high enough, that the single pixels are too small to be seen by the eyes of the spectator. The usual relative resolution for print is 300 ppi. For Posters, which are usually viewed from a bigger distance, lower resolutions are usual.

You can change the relative resolution without changing the quantity of pixels of the image. In this case, the quality of the image will not change, but it's size in analogue scale units will. The higher the resolution, the smaller the size. And vice versa. If the image consists of too less pixels right from the start, you will possibly get a result that is too small for printing.

In such cases, you can (up-) scale the image by using the Resampling. Then, the quantity of pixels will change and with it the quality, because there will be added (or deleted - in case of downscaling) pixels that must be computed outoff the colour values of the existing pixels. The image becomes either more pixelated or blurred (with Interpolation). And details, that are so small, that they couldn't be shown on the initial image, will of course not appear after upscaling (except AI is used).

So in generell it is a good idea, to always create images big enough to be printed, right from the start. Scaling always costs quality. But downscaling is less problematic than upscaling.

By the way, your image  - 3398 x 2903 x 72dpi (1196 x 1023mm) - will be 287,70 mm x 245,79 mm with a relative resolution of 300 ppi.

[*mark]

Thanks for all the responses

@GripsholmLion Yes I want an image you can't print - they're sample images for clients, and if my draft image is good enough to print, they won't bother with coming back for the finished image, or paying me for either. So, yes absolutely, I want something good enough to see, but too small to magnify without pixellation.   

If they're 'determined to print if they really want to', so be it, but it would be commercial foolishness to simply hand it to them on a plate. As a former PS user, the reduced image looks acceptable - then when it is magnified, the pixellation was really grainy - that's what I need here. 

As you suggest, I'll probably have to do some screen grabs, as also @Old Bruce suggests, with 'the resample box ticked' - yet doesn't make any difference. Very frustrating.

@iconoclast Thanks - that's helpful to know - especially the BTW at the end 👍🏻 

[Alfred]

24 minutes ago, *mark said:

As you suggest, I'll probably have to do some screen grabs, as also @Old Bruce suggests, with 'the resample box ticked' - yet doesn't make any difference. Very frustrating.

If you resize to something very small (e.g. by linking the W and H boxes and typing /=16 into either one of them, with the resampling method set to ‘Bilinear’ or ‘Nearest Neighbour’) and then bake in the new size by rasterizing the nicely pixelated result, returning it to the original size (via *=16 in this example) will retain the pixelation.

[GripsholmLion]

If you are sharing these samples by email or cloud storage, you can just simplify this; don't over think it. DPI/PPI is not relevant; the compression value and pixel dimensions matter. In this quick example, a 4500px stock image is about to be exported at 300px with heavy compression and the preview shows the effect of that compression. In addition, or alternatively, you may wish to add a watermark using your branding.

Also take note of Alfred's advice, which he has added as I'm typing this.

[iconoclast]

8 hours ago, Alfred said:

If you resize to something very small (e.g. by linking the W and H boxes and typing /=16 into either one of them, with the resampling method set to ‘Bilinear’ or ‘Nearest Neighbour’) and then bake in the new size by rasterizing the nicely pixelated result, returning it to the original size (via *=16 in this example) will retain the pixelation.

Yes, that's possibly important to say: every time you change the scale of an image (that means the quantitity of pixels), every pixel of the image must be freshly computed, and that always means a loss of quality (pixelation or blur). So if you want to reverse a scaling, do it with the Undo function, not by scaling back by inserting the initial measurements.

And to prevent some confusion: the term "Resampling" means what I said above: the computing of every pixel of an image. But it also stands for "Interpolation" in the Affinity apps. "Interpolation" stands for the different methods to recompute the pixels: Nearest Neighbour, Bilinear, Bicubic... Which method you choose will have an impact on the resulting quality. Nearest Neighbour and Bilinear are better for graphic things (they tendentially pixelate), Bicubic and the others for detailed photographs (they tendentially blur a bit).

And yes, of course also GripsholmLion is right, the compression is very important. It can ruin everything. Especially JPEG-compression always means a decision between file size and quality of an image.

[*mark]

Hi Folks, still in need of some expertise here...  Here's why simple image reduction doesn't work - at least not for me... (and TBH, I never had so many problems in the past) -

I've resized a 2mb image, unchecked 'resample', made it about (or so I thought) less than half the size, only to find that the file size has increased by around 200%, and the DPI increased to 425 from 180dpi, so I still end up with a bigger document by making it smaller?? Really?? 

I dislike citing PS, but when creating a smaller document, it's smaller, physically AND the file size - so why can't AP do the same?

And although AP image is physically smaller, it doesn't really help to send, or in future create 'thumbnails' from existing images at 425dpi @ 5.4mb...

So what am I doing wrong here? I simply want an image to fit on screen, about A4, that is sharp enough to see, but can't be magnified enough to print, but pixelates instead. Is there a simple way to achieve this?? Thanks

[iconoclast]

18 minutes ago, *mark said:

Hi Folks, still in need of some expertise here...  Here's why simple image reduction doesn't work - at least not for me... (and TBH, I never had so many problems in the past) -

I've resized a 2mb image, unchecked 'resample', made it about (or so I thought) less than half the size, only to find that the file size has increased by around 200%, and the DPI increased to 425 from 180dpi, so I still end up with a bigger document by making it smaller?? Really?? 

I dislike citing PS, but when creating a smaller document, it's smaller, physically AND the file size - so why can't AP do the same?

And although AP image is physically smaller, it doesn't really help to send, or in future create 'thumbnails' from existing images at 425dpi @ 5.4mb...

So what am I doing wrong here? I simply want an image to fit on screen, about A4, that is sharp enough to see, but can't be magnified enough to print, but pixelates instead. Is there a simple way to achieve this?? Thanks

As far as I understand, you want to make an image smaller, e.g. a 2000 pixel x 1000 pixel image shall become a 1000 pixel x 500 pixel image. So check "Resample", because you need to change the quantity of pixels, and insert the new values you want. "Resample" must only be unchecked if you want to change the relative resolution (for print). That will not change the quantity of pixels. In fact, the pixel input fields will be greyed out if you uncheck "Resample", so that the quantity of pixels can't actually be changed then. "Resample" means, that the pixels of the image will be computed new and their quantity will usually change. Without "Resample" the quantity of pixels will stay the same, but the resolution and in relation to it, the analogue size of the image will change.

The value of the relative resolution should not change with checked "Resample" if you keep your fingers off that field. But you can change the value manually in the same step, if you want. For screen, it will not be too important. This resolution thing is only important for print.

[GripsholmLion]

Bruce already advised you to enable resampling if you are trying to resize, in a very literal sense, by fewer pixels. Or if you follow my example screen grab, resampling is implied by reducing the pixel values in the inputs, as there is no explicit resample toggle in the File > Export window. Only a resample method.

45 minutes ago, *mark said:

I simply want an image to fit on screen, about A4

I'm not sure what you mean by that. The screen on which I'm typing this is about A4 size, physically speaking, but that has little to do with anything. As it's real pixel size is 2560 x 1600, any photo of at least 1440 x 900 can be viewed at full screen without a black border, for what it's worth.

If you don't want an image of those dimensions to be printable, please see my previous advice – and that from Alfred – about compression.