Saving TIFFs as JPGs

I'm sure there are lots of ways to do it, but if you use Gimp (open source graphics programme, free to use), you can import 32bit TIFF, change the precision to whatever you want, and export to jpg or png.
You can do lots more than that with it too!

Padraic Moran:
I'm sure there are lots of ways to do it, but if you use Gimp (open source graphics programme, free to use), you can import 32bit TIFF, change the precision to whatever you want, and export to jpg or png.
You can do lots more than that with it too!

Hi Padraic
I can change the bit depth in photoshop. But the problem is, it totally ruins the image

Peter Kestel:
In Photshop use the 'export as'.

Hi Peter
Unfortunately I don't have that option. The only available option in the Export menu is Paths to illustrator

Padraic Moran:
Hi Stuart, JPEGs are 8-bit images by definition, with lossy compression, so there will always be a quality drop when converting from TIFF, but it is usually not obvious unless you are pixel-peeping. If the quality drop is as bad as you say, then either Photoshop is doing something weird, or you're setting a very high compression level. Export As will usually allow you to configure output quality as a spectrum prioritising either image size or image quality but not both. Take a look at any of my Astrobin images as they're all 8-bit JPEG exported from Gimp as 90% quality, 4x4x4 subsampling.

I'm not a PS user but I read a post here (or on another forum) recently about PS 2021 changing the location of the Export As option.

Sorry Padraic, maybe I wasn't being clear. What I mean is that just changing from a 32 bit TIFF to a 8 bit TIFF (before even saving as a JPG) completely ruins the image for some reason. Here's what I mean;

Stuart.  I do not know your workflow but I can give you a few bits of basic advise.  It sounds like you are using Mode under Image in PS. and changing your DSS file to 8bits,  there is no need to do that as your DSS stacked image should be 16 bits in PS, leave it at 16 bits in PS, do not change it to 8.
Leave your Tiff file at 16bits for the entire time you work on it in PS.  When you are finished processing and have the perfect image you want, save it as a Tiff and keep it with all the other images you are finished with in a folder.  If it is not somehow 16 bits then go to mode and change it to 16bits, otherwise forget about Mode for now.
When it comes time to post your image on Astrobin take it out of your Tiff folder and put it back it in PS and save it as a JPEG, using the "save as" prompt under PS- File- save as- jpeg. This will leave your Tiff file intact and give you a new separate JPEG file that you can save in a folder. If you have reasonable internet upload and download speeds your image as a JPEG should be fine for Astrobin and there should be no visible change in your image at all.  There are probably 14 million other things you can do to an image in PS but I hope this helps for now.

scott

General advice is not to start with 32 bit from DSS.  Use its 16bit output, and start from that in PS.

When you down-convert a 32-bit image to a 16-bit one or an 8-bit one in PS, PS assumes that you need some gamma stretch or HDR processing, to compress the 32 bit of info into the lower bit depth.  This is like converting a linear image (typical for raw) into a nonlinear one (typical raw-to-TIFF conversion).  There may be ways to avoid this and maintain the linearity during the down-conversion, but this is entirely not necessary for most people.  Most people just don't need the 32 bit depth for processing.  When I still used DSS, I saved its stacked file as a 16-bit TIFF, and then go to PS.  No problem at all.

thanks for this advice everyone! It sounds like I should export from DSS as 16 bit, rather than use the native 32-bit autosave. TIF.

I'll try your various tips next time.

James Peirce:

Stuart Taylor:
I am a newbie at all this, so forgive the basic question..

I have been shooting in RAW on a DSLR and stacking in DSS. This gives me a TIFF which I then process in Photoshop. 

But I can't then save that TIFF as a JPG (to post here, for example) because of the bit depth of the image (it's 32 bits). But if I lower the bit depth to 8 bits to allow me to save as a JPG it completely wrecks the image and all my hard work!

Suggestions?

Can you elaborate on “wrecks your image”? Converting a final image to JPG shouldn’t much things up *too* bad, but you do want to pay attention to the amount of compression applied. When saving from most programs this is a setting you can control. Also, when saving high bit depth images with very subtle gradients it is easy for color banding to rear its head (especially if recompressed by whatever it was uploaded to). This is the nature of the beast to some extent, but can be mitigated in part by adding or preserving some noise/texture in the image (which is the best sort of noise reduction anyhow for deep space photography; some of that texture is best retained to avoid the “plastic” look that images can take on).

James - I posted the images above (before and after) so you can see what I mean about 'wrecking' the image! It went from a nice black sky with a nebula in it to a bright turquoise field with an over-exposed white blob in it! 

Well, I'm not sure on what you have done between the two M57 images you show above, somehow you have stretched the image.
I do (in PS CS6 menus) 16bit Tiff -> 8bit Tiff -> Save as xx.jpg all the time as the last step in PS CS 6 before I upload my images to Astrobin and/or other places on the internet.
Here I have taken a copy of your  first image (nice black one where the vigneting is hidden) and just stretched it using curves in Astroart.
http://www.dl.dropboxusercontent.com/s/0fm6uiajehfj3lt/M57blackWcurves.jpg?raw=1

James Peirce:
Is there a reason why you are doing this? In Photoshop a proper workflow is to import as 32 bit TIFF, perform any initial “stretching”, and then convert to 16 bit for all the remaining post processing. 8 bit shouldn’t be used for this thing in the Photoshop workspace or as a storage format for your master files; only when exporting to JPG.

Looking at how dark your initial image is, it does look like it should receive the initial manual stretching in Photoshop after being imported as a 32 bit TIFF.

The reason I was doing this was so I could save the image as a JPG (to post it here). You can't save a 32 bit or a 16 bit file as a JPG. Not in photoshop anyway.

But yes, I did all the stretching etc in photoshop using the 32 bit TIFF. But when I discovered I couldn't save it as a JPG, I merely screenshotted it (using snipping tool) so i could make a JPG to post here. 

Niels V. Christensen:
Well, I'm not sure on what you have done between the two M57 images you show above, somehow you have stretched the image.

Nope. I haven't done any stretching between the two images above. Literally all I did in photoshop was open the TIFF then Image > Mode > 8 bit

I haven't had any problems bringing in a 32-bit DSS TIFF file into Photoshop for processing.

No, neither have I. Opening the 32bit TIFF and processing it is fine. The only problem comes when I reduce the bit depth to 8 in order to produce a JPG.

Right.  Stuart you have all the information you need to fix your original problem and the fix is as you now know quite simple. 

CS, and  look forward to seeing your future images.

scott

James Peirce:

Stuart Taylor:
The reason I was doing this was so I could save the image as a JPG (to post it here). You can't save a 32 bit or a 16 bit file as a JPG. Not in photoshop anyway.

You should be able to save a JPG from any version of Photoshop. Which version are you using? There is a JPG option under “Save As” and “Export To”.

Nope. Not in Photoshop CS6. Neither Save as.. not Export provides a JPG option

Anyway, as wsg says I now have enough info to be getting on with. So thanks everyone!

Stuart,

I use Photoshop CS4 routinely to convert TIF images to JPG.  Open your TIF. Under the File menu, go to Scripts, then Image Processor.

In the dialog box that opens, in step 1, select Use Open Images. In step 2, select Save in Same Location.

In step 3, select Save As JPEG.

Then in the upper right corner, click Run.  This will Save your TIF image as a JPG in a new sub-folder where your original resides.

CS, Bob