Jpg noisier than Raw?

[nebulosity.]

It took a sub this morning with my Canon 350D on Jpg+raw and comparing the two subs the Jpg is way noisier with a million hot pixels and the Raw is pretty clean. Figure that?

Cheers
Jo

The first image is the Raw, then the Jpg.

[codemonkey]

My best guess is it's related to the curve that's been applied to the jpg vs raw (note how the black point is quite different on the jpeg) and the sharpening applied.

I think more interesting is the very large reduction in small stars in the jpg. Maybe there's a median filter or something being applied?

But yeah; always shoot raw if you can, especially with astro.

[jsmoraes]

I never did this test. But your photo jpg published here doesn't permit identify the dots as hot pixels. Are you sure that they are really hot pixels ?

Canon process RAW files to convert them in jpg. Actually, it always does the capture as RAW. It can output as jpg file, but after an internal convertions. And it uses many filters in this convertion.

[jsmoraes]

I downloaded your jpg photo and openned it in Photoshop. The dots seems to be stars. They have more than only one pixel, therefore they aren't hot pixel (damaged pixel).

Maybe there are some hot pixels, and maily some noise, but as you told million of hot pixels... What I saw in the photo jpg is large number of stars in the background. Those stars don't appears in the RAW file. Perhaps only after a graphic process.

[jsmoraes]

Many stars have a black circle at periphery. This is normal for jpg file, because of automatic contrast applied. If I well remember they are called Gibs Eyes, or something alike.

Just because these issues we always work with RAW files.

[nebulosity.]

Hey Jorge, if you would like to have a look at the full size you can download them at the link Here. (https://www.dropbox.com/sh/6dobuht9k2us8g2/AADvc8MnmVE8FXBza0lk7dNxa?dl=0)

There are the original files (jpg and CR2) and jpg versions.

I always capture in RAW so it doesn't matter much but it's interesting anyway.

Jo

[raymo]

It seems that Jorge is right, I set my screen to 500%, and the "hot pixels" definitely cover a several pixel area.
raymo

[cometcatcher]

That seems backwards. I thought the RAW would have been noisy. I dunno. But then I dunno anything lately. I think I'm getting old timers disease. Let us know if you figure it out.

[jsmoraes]

The zip file with CR2 has error, I can not unzip. The JPG files presents noise and some hot pixels. The white arrow shows normal noise, the blue arrow can be hot pixel: they are identical in all channels and very small (1 pixel ?).
The image is 150 %

[nebulosity.]

Yeah I know, I definitely thought that as the jpg's have been fiddled with by the camera they would have less noise, don't know what's happening :question:

[nebulosity.]

yes that is what I thought, very weird :confuse3:

[jsmoraes]

Jo, some noises for automatic processing are signals. Therefore when automatic processing they can appears.

There are differents kinds and origin of noise. The red arrow seems to show the light noise. Normal in a single light frame. Remember we shot many frames to reduce them with stacking.

The blue arrow arrow maybe is showing the eletronic noise that was not filtered by automatic processing. Or bad pixel. As they are with white color, perhaps they are electronic noise.

No matter, if the automatic processing didn't filter them, they will appears with more intensity than when you use and process the RAW file.

And you didn't tell about what ISO you used. What surely I can say is that the most weird dots are random noise, not bad or damaged pixel.

You can check the JPG convertion doing a JPG high quality shot alone. I don't remember if when you are using RAW-and-JPG the quality of JPG is high or low.

[LightningNZ]

Regardless, the JPEG looks like puke. The RAW has considerably more nebulosity showing because it's not letting the camera mess with the actual signal. You can correct for other artefacts using the standard model of bias, dark and flat correction - you can't do anything with JPEGs.
-Cam