JPEG quality difference

[irandar]

Hi folks, I always find that when I make a screenshot with Preview on Mac and then a jpeg that I always get better results than when I make a jpeg export from APv1.  Here is an example with the moon. Incidentally, I always get best results from a single shot than when stacking (not astro) 5 or so shots. The sizes are different but I think you can see the jpg differences.  Thanks and regards, Irving

[irandar]

The result from Preview is much more like the AP original.

[stokerg]

Hi @irandar,

I can see a difference but how much of that is down to the images being different sizes is very hard to say.  Can you attach your afphoto file that you taking the screenshot from and I'll be able to look into this.

[irandar]

@stokerg Hi,

The file is 250mb. Can you give me a box to download it? There is a large difference but why should that be? I have seen it often before. 

Thanks, Irving

[stokerg]

Hi @irandar,

Here's a Dropbox link for you  

[Pšenda]

7 hours ago, irandar said:

The sizes are different but I think you can see the jpg differences. 

The second image is full of image noise (or defective pixels?) while the first is not. So, was there any denoising before export, which in principle will worsen the sharpness of the image?

[irandar]

Hello Psenda, There was no denoising. The first smaller image was exported with APv1. The second larger image was screenshot copied with Preview on iMac and then exported with Preview as a jpeg. This image looks to me much more like the original on the AP screen than the smaller image. Both were 100% jpeg quality. Thanks for your help, Irving

[stokerg]

Hi @irandar,

Can you confirm the size you are exporting out of Affinity as?  Also if you resize the export from Preview to match the size of the Affinity export, how does it look?

I suspect this will be related to the exported size and the use of the multiple bandpasses that are applied in Affinity.  The larger image has been exported at full size, 5472 × 3656 and the smaller one (if correct) is 883 × 625, which is a lot fewer pixels to deal with.

[irandar]

Hi @stokerg,

Matching the dimensional size on the screen of the jpeg Preview does not change the quality. Not sure I understand what you are saying about the exported size. The main thing is that the Preview route gives a much better jpeg image, which best corresponds to the original AP. Here are the jpegs again redone. Notice the AP jpeg is 42mb, the Preview jpg 1.6mb and the original afphoto is 230mb. Why so many mb in the AP jpeg for a poorer image?. Do you see the differences? Thanks and regards, Irving

[thomaso]

On 11/8/2023 at 10:44 AM, irandar said:

when I make a screenshot with Preview on Mac and then a jpeg that I always get better results than when I make a jpeg export from APv1.

15 minutes ago, irandar said:

The main thing is that the Preview route gives a much better jpeg image,

How do you "make a screenshot with Preview" (or do you mean the macOS screenshot feature?) – And in what way do you mean "better"?

It is not useful to compare your results without knowing the compression rate + resampling methods in both processes. From your file names it appears that the Preview result has obviously less quality than the APh export (assuming "editnewjpg" refers to the APh result) … while it is unclear for what reason the Preview result is titled on the image with "Soften Structure".

34 minutes ago, irandar said:

Not sure I understand what you are saying about the exported size.

Like with compression & resampling for a useful comparison also the image pixel dimension matters … and thus the zoom level: your recent examples have quite different size and thus they can't match in detail quality: Preview: 1474 px | APh: 5472 px width. – With other words: It is a comparison of apples with pears.

[irandar]

Hi thomaso, On my iMac 2017 is an app called Preview. It may use the same screenshot method but it also has a export feature. Not sure which are apples and which are pears, but the Preview version looks sharper, similar to the AP file. The smaller file size gives the sharpest result in this case. Does the preview version look sharper to you? Regards, Irving

[irandar]

Hi thomaso, Are you sure you did not get these images switched around? I would expect the sharper and grainier from the Preview and the blurier and smoother from the AP jpeg. How did you make these closeups? Regards, Irving

[thomaso]

1 hour ago, irandar said:

the Preview version looks sharper, similar to the AP file. The smaller file size gives the sharpest result in this case.

41 minutes ago, irandar said:

Are you sure you did not get these images switched around?

My screenshots were done in the forum's browser window, so the file names in my screenshots appear to be yours.

To judge the sharpness of two images they both have to be displayed in the same zoom level, whereby you get the most reliable display if you set the zoom level to "Actual Pixels" (APh: shortcut 'cmd 9' | Preview: depends on your app preferences).

If, to your eyes, indeed "the smaller file size gives the sharpest result" then I don't understand your question or problem. Nevertheless, my experience is opposite to yours.

If you indeed want to reduce the file size of your exported APh image you can …

• reduce the image's pixel dimensions,
• increase the compression rate for export = reduce the "Quality" value
• choose the resampling method "Nearest Neighbour" or "Bilinear" (not "Bicubic" or "Lanczos…").

[irandar]

Again I find JPEG quality difference. Here is a jpg and a screenshot, which is much more like the af file. Have a look please. 

[thomaso]

30 minutes ago, irandar said:

Again I find JPEG quality difference. Here is a jpg and a screenshot, which is much more like the af file. Have a look please. 

Again you did not tell the JPG export settings while you compare JPG with PNG.
And again the zoom levels / pixel dimensions are different, resulting in less details for the screenshot.
And again, to me the JPG shows definitely more/better quality than the screenshot (png): not only regarding size/pixel dimension but mainly regarding contrast and halftones.

Honestly, meanwhile I lost your concern and don't fully understand the entire comparison: Do you export from APh – or export from Preview?  It could help for the forum discussion if you include parts of the app interface in your screenshots to make it easier to assign the correct app to the uploaded image details. Also, since you mention the appearance in APh: is the screenshot taken from the original file viewed in APh – or taken in Preview from another file?

Below one common screenshot of your two pictures, displayed in Preview. – left: JPG | right: screenshot/PNG. – Do you agree that the left/jpg shows the better quality? If yes, what do you want to tell or ask? While I actually would expect quite identical quality in an export & a screenshot (if both get displayed in 100% size) I wonder what is causing the imho obvious, large quality loss in your screenshots, and why do they result in a different size/less details?

Might your thread possibly concern profile issues in your system and applications? (though that would not explain the massively blurred, softened result in your screenshot from 9th November)

[irandar]

The export on jpg was 100%. The screenshot is from my imac. I am mainly bothered by the color change. I had to change the jpg size to satisfy the file size limit here. Many thanks for your time. Regards, Irving

[thomaso]

47 minutes ago, irandar said:

The export on jpg was 100%.

Again: from which application?

48 minutes ago, irandar said:

The screenshot is from my imac. I am mainly bothered by the color change.

Which confuses me, since you appeared to consider/judge/see the screenshot as better quality than the exported jpg – while to me their qualities appear opposite.

Note, a screenshot can take different data than you see on screen (you can do a screenshot of a defect monitor without shooting the defect / you can screenshot an image successfully from an external monitor if it is plugged but switched off (displays black).

So we might need to see all your colour profile settings, in macOS and Affinity preferences + Affinity document + Affinity export.
The Preview.app > Info panel reports to me for your screenshot "iMac" as profile name. Is this a default system/Apple profile for your hardware or is it a custom named profile or one from a different hardware or system?

54 minutes ago, irandar said:

I had to change the jpg size to satisfy the file size limit here

The resolution differs between the export and the screenshot: JPG: 96 dpi | PNG: 72 dpi. – To compare without the need to set different zoom levels: Make sure both get created with the same resolution.

[irandar]

The colors are the same, screenshot and affinity. It may be the dpi is lower but one does not see that. I do not know how to make the resolution the same, jpg and screenshot.  Thanks

[Pšenda]

11 minutes ago, irandar said:

It may be the dpi is lower but one does not see that.

In the case of 100% display (one image pixel to one screen pixel), is DPI irrelevant - pixel is pixel.

[thomaso]

3 hours ago, irandar said:

I am mainly bothered by the color change.

1 hour ago, irandar said:

The colors are the same, screenshot and affinity.

I can't follow, to me it sounds contradictory.

53 minutes ago, Pšenda said:

In the case of 100% display (one image pixel to one screen pixel), is DPI irrelevant - pixel is pixel.

Not necessarily for Apple's Preview.app which has a preference setting for either/or and thus may show different sizes for 100% zoom level. However, resolution does not seem to be the relevant part in this thread about "JPG quality difference", screenshot vs. export, colour or/and contrast.

[irandar]

I guess I could edit the jpeg to bring the colors up.

[irandar]

Back to this color change between jpeg and Affinity: Do you see the color differences in the files I downloaded?

[thomaso]

34 minutes ago, irandar said:

Back to this color change between jpeg and Affinity: Do you see the color differences in the files I downloaded?

As I mentioned various times, yes, I see differences in colour, in contrast, in amount of details. But until now I thought that the JPG is the Affinity export and the screenshot.PNG is taken from Preview. It seems to be unclear from the beginning: it made you ask me whether I did switch /  rename your files for my common screenshot of both moon files including their file names:

On 11/9/2023 at 1:58 PM, irandar said:

Are you sure you did not get these images switched around? I would expect the sharper and grainier from the Preview and the blurier and smoother from the AP jpeg.

I still wonder how the label "Soften Structure" (in a rounded rectangle) came to the blurry version of the moon and I still don't understand why you think I did mix the names, though I also can't imagine you see the quality in this two images opposite to me. (you can download your uploads to check them) – unless you view / compare / screenshot at a zoom level other than 100% pixel size.

To me the confusion began with your initial post: you wrote about two JPGs + one screenshot:

On 11/8/2023 at 10:44 AM, irandar said:

I always find that when I make a screenshot with Preview on Mac and then a jpeg that I always get better results than when I make a jpeg export from APv1.

While I would expect better quality from an APh export than from a two-step version of screenshot -> export you seem to expect it vice versa.

Now back again:

1 hour ago, irandar said:

Back to this color change between jpeg and Affinity: Do you see the color differences in the files I downloaded?

You write about downloaded files. Does it mean you downloaded them and if yes where from? Or do you refer to your uploaded files and just call it downloaded erroneously?

Also now, in your last post, you ask about a colour difference, while you wrote recently there would be no colour difference:

18 hours ago, irandar said:

The colors are the same, screenshot and affinity.

So again I recommend to make your uploads more clear: screenshots should show parts of the interface of the viewing app. And exports need to be named more clear. The file names in your last uploads seem to indicate that the JPG was an export while the other is named "screenshot" but you still did not tell what application did the export (I assumed it was Affinity). If the export was from Affinity then your last post is confusing/contradicting when it says: "color change between jpeg and Affinity." Does this mean that this time the screenshot is from Affinity and the export from Preview? If yes, from what file was the export in Preview done? And in what zoom level was the screenshot displayed?

As mentioned before: Preview has a preference for zoom level and display size. Make sure you use the option that shows real pixel size, regardless of resolution/dpi/print size. Your preference dialog window in Preview might have a different design but I assume the option exists, too:

Also I recommend to upload your files packed together in a .ZIP, this will avoid the change to metadata by the forum software (e,g. stripping the creator app and the colour profile) and recompressing.

And I still think it may be useful that you show your colour profile settings, in both macOS and Affinity.