Help With Reducing File Sizes for Large Images

[Moviefan2k4]

I've run into a somewhat frustrating problem, when trying to save some of my bigger images in Photoshop. The CS2 version doesn't have the Export As option, and when I try Save For Web it says my computer doesn't have enough memory (I have 8 GB installed in my tower at the moment). I have a lot of images that are hundreds of MB in size, but my online hosting site has a limit to files of 10 MB or lower. I don't want to resize the image dimensions, and I'm concerned about dragging the regular Save slider too far to the left, fearing it will degrade the quality of the images I'm trying to preserve. Any ideas? Thanks in advance.

 

[thebestcpu]

Hi @Moviefan2k4

Quality is degraded when using a lossless compression format such as JPEG, yet the compression algorithm hides it pretty well. As compression gets higher (lower setting), it can become noticeable.

One point of clarity. Is the size of the very large MB images already compressed in JPEG or is this the size as reported by PS?

What ends up being acceptable compression depends on
- How large will the image be viewed or printed
- Original quality of the image (lower quality also masks JEPG artifacts)

Lower the JPEG size of a fixed pixel dimension image size comes too
- higher compression (lower setting)
- reducing the high-frequency content in the image e.g. slight blur (which may or may not reduce quality as well)

I think the best way to give a better idea of what is possible and to show you the quality loss is to link one of your higher MB images (or a crop of a piece of it), which you want to get below 10 MB, to see what forum members can do for you. If you do provide a cropped version, please also provide the original pixel dimensions as well.

Just a suggestion
John Wheeler

 

[dannac]

Any ideas?

This program does a good job at resizing.

FastStone Photo Resizer - Powerful Image Converter/Resizer

 

[thebestcpu]

Yo expressed concern about how much compression can be applied to an image so that it can be posted to a website under 10MB and preserve pixel dimensions.

I took an image from your website with the image of Harrison Ford for the movie Air Force One.
The dimensions of the image are 5904x6988, which, if saved with no compression and 8-bit depth per color channel, would be 123.9 MB

As saved as JPEG on your website, it was 7.4MB, which already has about 17x compression.

I wanted to show that sometimes, the best way to know if you are losing a quality is just to do a side-by-side comparison.

What I did was compress the image down to 0.67MB, or a total compression of 185X

Then, I compared the images side by side at 100% for comparison.

1) Full-color RGB, as would be seen on the website
2) Just the Luminosity channel, which JPEG prioritizes for quality
3) Just the Saturation channel where JEPG is more highly compressed
4) Just the Hue channel where JEPG is highly compressed.

Even with the color components highly compressed (16-bit data block squares), the eye does not have a good resolution for color but rather a higher resolution for luminosity. So, even with these compression elements, the overall image still looks pretty good.

This might be a better way to judge how much to compress your images without worry.

Here is the original whole image as a crop of a screenshot:




Here is a blow-up around Harrison Ford's eye. The original is on the left and compressed on the right.



Here is the same comparison with just the luminosity component



Here is the same comparison with just the Saturation components



Here is the same comparison with just the Hue component



This may not give you a hard number of how much compression to make, yet it may be an approach to determine on your own.

I hope you find this helpful.
John Wheeler

 

[Moviefan2k4]

I tried that program you sent my way John, but with the bigger files it didn't reduce them very much. I managed to get some of my images that were about 15 MB to below 10, but that's it.

 

[thebestcpu]

I tried that program you sent my way John, but with the bigger files it didn't reduce them very much. I managed to get some of my images that were about 15 MB to below 10, but that's it.

Hi @Moviefan2k4
It was @dannac who pointed you to Faststone.

The offer is still open if you want to provide a link to one of your larger files for examination and recommendations.
Not a must, yet for me, I believe that is what I would need to provide anything other than generic recommendations.
If that is not an option for you, maybe another forum member will be able to help.

John Wheeler

 

[Moviefan2k4]

Hi @Moviefan2k4
It was @dannac who pointed you to Faststone.

The offer is still open if you want to provide a link to one of your larger files for examination and recommendations.
Not a must, yet for me, I believe that is what I would need to provide anything other than generic recommendations.
If that is not an option for you, maybe another forum member will be able to help.

John Wheeler

This one is from my old MediaFire account, which I was surprised to learn I still had access to. Its almost 35 MB in size, but if you want to try and get it below 10 without shrinking the size, be my guest.

Hobbit_Journey_Gollum_keyart1

MediaFire is a simple to use free service that lets you put all your photos, documents, music, and video in a single place so you can access them anywhere and share them everywhere.

www.mediafire.com

 

[thebestcpu]

Hi @Moviefan2k4, thanks for the image for me to try (or any other forum member).

I had to pull a post as the Save for Web functionality only allows up to 8192 pixels on a side, so I just used the regular Save As set for JPEG, and the result was ~2MB.

Here is a screenshot of the entire image, which is 7350 x 10650 pixels in dimension which, with no compression and 8-bit depth, would be 224 MB



I am showing a side-by-side comparison of the image downloaded at 36.6 MB, which is already a large reduction. The image you provided is on the left and the 2MB compressed version is on the right.



You can see some differences, yet not much. Reducing it to 10MB instead of 2MB would be quite a bit better, yet I wanted to show the difference at maximum compression.

Here is the Dropbox link for the full-size compressed file for you to do your side-by-side quality test. I can provide a 10 MB version if you want as well.

https://www.dropbox.com/scl/fi/2ou9...ssed.jpg?rlkey=z2hrbm47tor2ghmc1yz6tn2l9&dl=0

If you have more questions, ask
John Wheeler

 

[thebestcpu]

I had a few extra minutes and compressed the image to only 8.7 MB
Here are the screenshots with the preview "off" in the first image and the preview "on" (compressed) in the second image.
Technically, quality is lost when compressed visually at an average viewing distance at 100% magnification. I could not see any degradation.
I hope this incremental image/information is helpful
John Wheeler

The original is at 100%, with the preview box unchecked.




Here is the image with the preview box checked (note that the JPEG Options box predicts the file will be 8.3MB, yet when checking the actual size in the file manager, it was 8.7MB:

 

[Moviefan2k4]

The CS2 version doesn't have the file size number, below the Preview checkbox. So I have no idea what kind of quality loss I'd be imposing on my images.

 

[thebestcpu]

Hi @Moviefan2k4

From a CS2 manual, you should have the image size at the bottom of the panel instead of under the preview checkbox per this image. It has been a long time since I had CS2, yet I remember sometimes it takes a while for the Szie number to show up. I don't know what other limitations that CS2 has.

Note that knowing the quality cannot be done just by file size or the slider number. It can be done by either looking at the image preview at 100% magnification or saving the file, pulling it back into Photoshop, and examining it at 100% magnification. You can also verify the size with the PC/Mac file manager to verify the actual file size as a workaround.

These approaches may not be as easy as you want, yet older versions of Photoshop do not have all the features of newer versions, so one may have to use a workaround to meet their needs.

So whether the size shows up at the bottom of the screen or saving the file and examining it in the file manager, one can determine the final size. Also, by previewing or importing the compressed file, one can visually see the compressed image and judge the quality.

If you do not want to upgrade to Photoshop, other low-cost and free pieces of software can compress and preview the JPEG image that has already been posted (FastStone).

One thing you have going for you is that with the large pixel dimensions of the image, compression artifacts are harder to see than when using an image with smaller pixel dimensions. The other thing you have going for you is that with such high pixel count images or what would end up being a very large prin (2 to 3 feet in dimension), it is unusual for a viewer to examine the image from very short distances.

The only real downside of the compressed image is that if one wants to crop to a very small part of the image and greatly enlarge it or to do more post-processing on the very compressed image, then the JEPG artifacts could become more prominent. That is not an issue if you have your original files to fall back on or link to the customer.

I think I am at the end of my ideas on how to help you, so at this point, I hope this helps, and I wish you well on your project/endeavor.
John Wheeler







very shor

 

[dannac]

I tried that program you sent my way John, but with the bigger files it didn't reduce them very much. I managed to get some of my images that were about 15 MB to below 10, but that's it.

The program I linked to will bring your 35.7mb to 5.8mb.