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Impact of resizing up when exporting from raw to jpeg.

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Solway Moss

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Feb 4, 2014
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Cumbria UK
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Hello everyone, this is my first post. I am photographing insects in my garden and having to crop quite drastically. I am using a Canon 1DX at 18MP RAW and finding the cropped files are too small to submit to Alamy. How does increasing the height and width dimensions when exporting as a jpeg in LR5 affect the quality of the image? The Alamy Forum has mentioned SoLD, but how much of an increase could I get away with before this becomes visible? I don't have Photoshop and this isn't for printing.

Many thanks.
 
Hi Solway, welcome to Lightroom Forums.

There is not really a simple equation to be applied to a situation like this.
In common with printing how much resampling one can get away with before image quality becomes visibly degraded is as much matter of the image and what is in it as it is about how many pixels one starts with.
Rules of thumb are far too vague.
Really the only way to do this is by trial and error.

In your situation what I would do is take an image that is developed and cropped optimally and then do a series of exports with increasing resampling.
Closely scrutinise the results on your own monitor.
There will be a certain cut-off beyond which the results become poor.
This is a subjective judgement and how far you can go will vary image-by-image but you will soon get a feel for the process.

Tony Jay
 
That's great, thank you. I have already started peering!
It would be so useful to have megabytes available in metadata - I see the MPs in Loupe Info and the file dimensions, but I can't find MB's - Alamy specifies minimum of uncompressed 17 MB file after cropping. How do I go about working out how big my cropped RAW file is so that I can perhaps tweak the crop a little without having to compromise when exporting?
Many thanks.

Edit: Or could LR not tell you in the export panel once you've set format, quality/resizing, how many MBs your image is going to be?
 
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Trouble with that Tony is that it's "after the fact", i.e. after the image has been cropped and exported, which means if it's too small the OP has to go back and try again.

Having said that, I don't think there's anything in Lightroom that would help determine how large a cropped image would be after export, all you have is the original file size and the cropped pixel dimensions, nor is there anything suitable in the Export module (you can tell Lightroom to make sure a file is no smaller than a specified size, but you can't tell it to make sure the file is at least as big as a specified size). Might be a useful feature request, if it hasn't already been made.
 
Everything the OP is doing right now is trial-and-error Jim.
I think he will find however that the resized JPEG's will come in well below the prescribed limit that he mentions.

Tony Jay
 
But I am juggling the crop now, to keep upsizing to minimum. Would still be useful to know how many MBs I am gaining although the file dimensions are a good guide. Normally this wouldn't be an issue, but these bees are so small with many interesting diagnostic features and even with a 180mm macro, they still get spooked if you come too close.
Thank you so much for your help.
 
Hello Tony and Jim,

FYI the formula I am using to work out if a cropped Raw file is going to be big enough for Alamy is height x width x 3 divided by 1024. This gives me a rough idea before exporting as jpeg of how much I need to adjust the crop. By the way, your new radial filter is fantastic for the little bees - fits around them perfectly and so simple to use.
 
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