lost pixels

C

cladav

Messages
9
Name
David
Edit My Images
Yes
I am old hand at film but new to digital. My problem is losing pixels when saving to jpeg. Starting off typically with 5Mb image after doing very minimal editing (once no editing as experiment) and then saving to jpeg I finish with say a 2Mb image. I realise jpeg is a compression tool but most comps etc ask for jpeg images. I have set compression ratio to minimum which helps but only slightly. How do I edit and save an image to jpeg and only lose the pixels affected by editing.
 
Don't save it to JPEG until the last moment, save it as a lossless TIFF or better still as a DNG, imported into a lossless workflow (like lightroom)
 
As above, I tend to work in the RAW format and, when all edited and so on, export it as a JPG. You will not drop any quality working that way.
 
You don't say what image editing program you use, but a sensible work flow is (1) save the original, work on a copy (2) edit and save as a .psd if working photoshop, or a .tiff if some other brand of software (3) save a copy of your edit as a .jpg for sharing.

You will inevitably keep losing pixies as you edit, save, close and then re-open, edit save etc.
 
two responses both say save to jpeg at conclusion, which is fine but I gather from the response that there is no way around this loss
 
image editing is paintshop pro9, but i have tried others with same result
 
A question that has been missed is, what quality setting are you using, unless I have a specific reason I always save JPEG's at 100% Quality :thumbs: and often find that my file size increases after editing :thumbs: so check your settings :D

Also welcome to the world of digital and to TP :thumbs: :wave:

Matt
MWHCVT
 
MWHCVT said:
A question that has been missed is, what quality setting are you using, unless I have a specific reason I always save JPEG's at 100% Quality :thumbs: and often find that my file size increases after editing :thumbs: so check your settings :D

Also welcome to the world of digital and to TP :thumbs: :wave:

Matt
MWHCVT
Click to expand...

Matt is right, always choose the highest quality jpg setting. However jpg is a 'lossy' file format, no way round it. Welcome to the world of digital!!
 
Photodiva said:
Matt is right, always choose the highest quality jpg setting. However jpg is a 'lossy' file format, no way round it. Welcome to the world of digital!!
Click to expand...

I must admit most of my work these day's is done in RAW then saved as a JPEG :D a funny thing I have noticed is that in RAW I don't seems to have any hot/cold/dead pixels where I have approximately 25 in my JPEG long exposures because I do shoot RAW+Large JPEG :D

Matt
 
thanks for welcome! re quality setting I have heard this mentioned before but have not found how to access it in paintshop pro9 - Is this a photoshop facility
 
Thanks for your patience everybody who has responded I am just beginning and learning all the time - looks like I may have to scour my editing software for quality setting or change to photoshop
 
Thanks for making me investigate - I have found quality setting in software set it to max and 4.44MB image save to 7.4Mb not sure how this can happen but am not complaining, very happy
 
cladav said:
Thanks for making me investigate - I have found quality setting in software set it to max and 4.44MB image save to 7.4Mb not sure how this can happen but am not complaining, very happy
Click to expand...

I'm pleased we have been able to help you out :thumbs:

Matt
 
Unless you are cropping your image, you are not losing pixels. Pixel wise, I am sure your image is the same length and width after saving as it is before. What you are losing is information with regard to colours etc within the image. The more you compress an image, the more information you are losing, which ultimately will give you an inferior image. However, this inferiority only becomes noticeably apparent if you are working with large output, where any loss is more obvious than images at typical web use sizes.
 
ref dereks (scarecrows) input - I am clearly not understanding the difference between pixels and Mb's - when I save with 'normal' compression (whatever that is) the Mb's goes typically from 5 to 2. I thought Mb was another way of counting pixels but from what derek writes the pixels are the same (without any cropping) and so by my logic the Mbs should be the same. where am I going wrong
 
The compression process removes information from the image, but not pixels. The software bunches pixels together and than uses one colour value to represent those grouped pixels rather than a colour value for every pixel. If each pixel has a value for colour, and with a compressed image an area of 8x8 pixels has a value for colour then that is a lot of data saved.

Depending on the amount of compression, and the image, you may or may not see some degradation of the image, at least at moderate compression. With large amounts of compression you may start to see the effects of the compression process.

It is more involved than I've described, but hopefully my example gives you an idea how file sizes can be reduced but the pixel dimensions can stay the same. You can get more information about the process here.

As an exercise take a picture, and then re-save the image with 10% quality and then zoom into each image and compare. You should see a lot more 'blockiness' in the heavily compressed image by comparison to the original.
 
thanks redhead 17 your explanation makes sense if the image size is a measure of the different colours in the image. ie the number of colours is reduced but the pixels remain the same. (more pixels with the same colour value). so a completely white picture could 1 byte and several thousand pixels.
 
cladav said:
thanks redhead 17 your explanation makes sense if the image size is a measure of the different colours in the image. ie the number of colours is reduced but the pixels remain the same. (more pixels with the same colour value). so a completely white picture could 1 byte and several thousand pixels.
Click to expand...

You've got it. JPEGing is a mathematical process to make the file sizes smaller and more manageable, without necessarily losing any visible data at all. Every image you see - on here, magazines, books, on TV, whatever - will be a JPEG with almost zero exceptions. A high quality JPEG is very very good!

Similar example to yours - a large area of clear blue sky, all the same tone. On the original Raw it might occupy 4mp. Now you can either write that code data as 0101010101010101 four million times, or as simply 01x4m, you get the idea. The result in both cases would be identical.
 
I think confusion has been caused for me with some comps asking for min Image size of 1Mb - leading me to believe image size (Mb) was measure of quality it seems that this is not the case
 
cladav said:
thanks redhead 17 your explanation makes sense if the image size is a measure of the different colours in the image. ie the number of colours is reduced but the pixels remain the same.
Click to expand...

The number of colours would remain the same, but the number of pixels with a separate colour value would be reduced.

cladav said:
so a completely white picture could 1 byte and several thousand pixels.
Click to expand...

Not quite, because although in Jpeg compression each pixel wouldn't have a colour value, groups of say 8x8 pixels would, not just the whole image with one value.

It is not just the colours that affect the file size, but also detail in the image, which is related to the number of pixels with separate colours. A picture of a sky with the odd fluffy white cloud will probably have a smaller file size than a picture of bush with lots of detail.
 
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