How to Reduce Image File Sizes?

[Linda Lou]

I frequently get an error on a website where I upload banner images to that the file cannot be over 5 mb. All my banners measure 900x300, but some files are quite large. I don't know what is causing that. Is it the amount of layers that I've used in my draft that does that? Does "Merge Visible" not remove the hidden layers I'm not using? It is really frustrating to spend hours on a project only to find out that the file is too large. What can I do to avoid this? I've fixed some by opening a new image and pasting sections from the original. There must be a better way!

[rondo]

Go to File, Jpeg Optimizer, set size and then export to what folder you want.
PNG Optimizer in same menu also.

[Linda Lou]

Thank you! I usually upload .png, but I suppose Optimizer will work for that as well.

[hartpaul]

File size has been asked aboutr a number of times so I thought I might prepare some information.
I prepared a 900 x 300 pixel image and saved it as a bmp, png, jpgs with compression 1, 10, 20 and 99.
I then did the same with a graphic image filled with fishes pattern and again with a complex photo, and lastly the same complex photo with a photo portrait addition.
The image saves nd their sizes are shown:

Note:
1. In all cases the bmp takes the most amount of disk space.
2. For a plain white object where each pixel has the maximum channel value R=255, G=255, B=255) and no matter what the compression the jpgs are all the same and take more space than the png. This is because of teh overheads involved in a jpg.

With a simple graphic of a fish pattern much changes :

Note:
1. Now all the jpgs except the most highly compressed use more disk space than the png.
2. So pngs are good for basic graphics in saving space.

When it comes to photos another major change becomes obvious.

Note:
1. The png and bmp take up most disk space and the jpgs take up less space the more the compression.

Now some images can have a main subject and a background with all being sharp whereas the background is not required to be sharp. This means that you can actually use a soften brush to soften the background details so directing attention to the main subject. This in turn can make a decrease in disk space of as much as 35%.

Note : Here you can see the effect of softening the background. I even softened the black circled area even more and if that was done to the rest of the background then a saving of 40% or more in disk size could be made.

The OP has mentioned that they had a problem in keeping the disk size to less than 4MB (4000 KB).
As you can see in the file info above , none of my images of the same size even exceeded 1 MB.

So perhaps more info is needed from the OP.

[JoeB]

That is some extremely detailed and informative stuff you just posted, @hartpaul! I particularly learned from the tip about blurring/softening background where that data wasn't really the focus of the photo, leaving the subject in focus, and how that effectively reduced saved file sizes. While we should have known intuitively that your process would have that affect, we often simply forget the principles behind the graphic work we do. A lot of work on your part, good info and an excellent reminder for us to think about the principles behind the stuff we are doing with PSP!

[hartpaul]

Thanks Joe. I am also working on another idea that cause trouble, PPI v DPI and how people confuse the ideas of quality of image with those items. More later

[JoeB]

Thanks Joe. I am also working on another idea that cause trouble, PPI v DPI and how people confuse the ideas of quality of image with those items. More later

I know that you're already aware that I'm a real harpy on the subject of the difference in the terms - and the meaning of - PPI vs. DPI, and of people posting about questions that actually concern PPI but calling it DPI. I posted what seems to have been a well received explanation of PPI in this forum here:

viewtopic.php?f=56&t=61213#p339324

I haven't done a similar post about DPI because I just thought that once people realized that this term only referred to printer specifications, and wasn't something that most people who use inkjet printers would really have to concern themselves with, perhaps it would not be needed. When actually printing, people just choose draft, normal, or photo settings in their printer software. The printer specifications alone will determine how the printer both allocates and distributes the dots of ink it ejects per inch of paper, otherwise known as DPI.

That's unlike PPI, which is set in the graphic editor, and which tells the printer how many pixels of the image in their editor will be printed on one inch of paper. This is important for graphic program users to understand if they want to send their graphic output to any printer and know how that will affect the quality of printed output. And, of course, no matter what graphic editing program you use, you can't control the printers DPI (which is a printer specification only) but only control/set the PPI of the output from your graphic editor.

[jayson1945]

I know that you're already aware that I'm a real harpy on the subject of the difference in the terms - and the meaning of - PPI vs. DPI, and of people posting about questions that actually concern PPI but calling it DPI. I posted what seems to have been a well received explanation of PPI in this forum here:

viewtopic.php?f=56&t=61213#p339324

I have just had a look at the JoeB link. I would advise anyone to have a look also if you're a simpleton like me and have always struggled to understand PPI etc. A useful explanation of how image files are made. Thanks

[flagpole]

There's a bug...
When you save as .png without going through the optimiser it actually saves as .bmp but with the .png extension.

[hartpaul]

What bug? Is this 2018 you are talking about as you do not have it mentioned in your profile info.
How are you determining that it is a bmp with a png extension?
Just tool 4 jpgs and saved as png and bmp directly - no optimiser and the png s were consistently smaller than the bmp files
PSP 2018 version 20. 2. 0. 1

[LeviFiction]

I did the same, I even went into the raw data and confirmed the formatting was PNG and not BMP. Also in PSP2018. i also tried PSP8, and XI, an X2. No such luck on finding a bug like that.

I will point out that scripts need to be careful. All of the file extension logic is stored in the dialog box. So when you save out, if you don't have your script setup to save as PNG then it doesn't matter that you put "PNG" as your extension. It'll still save as whatever format is listed in the parameters. But that's the closest I'm aware of.

[flagpole]

I've not looked at the raw file... But the sizes are exactly the same.

I've just got in to the habit of saving png's via the optimiser. I'll have a run at it tomorrow and see if I can reproduce it.

[flagpole]

I did the same, I even went into the raw data and confirmed the formatting was PNG and not BMP. Also in PSP2018. i also tried PSP8, and XI, an X2. No such luck on finding a bug like that.

I will point out that scripts need to be careful. All of the file extension logic is stored in the dialog box. So when you save out, if you don't have your script setup to save as PNG then it doesn't matter that you put "PNG" as your extension. It'll still save as whatever format is listed in the parameters. But that's the closest I'm aware of.

So i've got a file for you...
http://nigelcoldwell.co.uk/84twiddlebolts.rar (188K 2.5Meg-unrared)
http://nigelcoldwell.co.uk/84twiddledbolts2.png (95K)

I've been working on this for an hour or so, saved it as .pspimage, then .png. The png is massive, 2.5Meg where as when i save it through the optimiser (full colour, alpha transparency) it's 95K.

The 'header' is below
PNG
XML:com.adobe.xmp <?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="XMP Core 5.1.2">
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<rdf:Description rdf:about=""
xmlns:photoshop="http://ns.adobe.com/photoshop/1.0/">
<photoshop:History>

I've been trying to recreate this since i left this thread.

[LeviFiction]

When you save as .png without going through the optimiser it actually saves as .bmp but with the .png extension.

Flagpole this is the portion of your post that we were responding to. Yes it's extremely large, but it's still a PNG. A perfectly valid PNG, I verified each part of the file with the PNG standard. Your image is 1710x891 pixels. It's saved at 8-bit per channel RGB with full transparency so 32-bit per pixel format. Without any compression that's 5MB. So it is being compressed. A BMP of this image is 4.36MB.

So you claimed it was actually a BMP format with a PNG extension. When in fact it's just a really huge PNG. That's all we were saying..

[flagpole]

Why's it so big?
I was obviously mistaken in saying it was saving as a bitmap. I hadn't given it as much though as I should have. It was just the similarity in the sizes.

I mean what is the point of compression if it's including all that junk?