Guide
Make Background Transparent
Short answer: for almost every photo this is a single decision taken one pixel at a time — this pixel is background, delete it; this pixel is subject, keep it. That works because the background sits entirely behind the subject. The exception is the subject that is itself partly see-through: glass, chiffon or tulle, smoke and steam, spray, thin hair, a soft shadow. There the correct value for a pixel is neither fully deleted nor fully kept but a fraction, and no single position of a single slider produces a field of fractions. Two checks sort your picture in about ten seconds, and the table below is the sort.
Which of the two are you holding?
| What is in the picture | What the pixel needs | What a colour key gives you |
|---|---|---|
| A person, a product, a solid object against one colour | Delete or keep — nothing in between except at the outline | Correct. This is the case every guide, including this one, is written for |
| Glass, a bottle, a lens, a window; chiffon, tulle, a net; smoke, steam, spray | A fraction, across a wide area of the subject, not just at its outline | Two wrong answers. Keep it and the old background colour stays trapped inside; delete it and the object disappears |
| A soft shadow or reflection the subject casts on the backdrop | A gentle ramp from nothing to a little | Deleted with the background — which is why the object looks pasted on and slightly airborne |
The rule that holds for everything else
A background removal is normally one question asked of every pixel in turn: how far is this pixel’s colour from the colour you nominated? Far away means subject, keep it. Close means background, delete it. Everything a colour tool does — sampling, tolerance, edge softness, spill removal — is a way of answering that one question or tidying the answer.
This works because of an assumption nobody states: the background is entirely behind the subject. The subject hides it. Where the subject is opaque, the pixel either belongs to the subject or it does not, and there is nothing to be uncertain about.
Where the assumption breaks
A see-through subject breaks it because the background is not behind the subject — it is visible through it. That pixel is genuinely both things at once. The right answer is not background and not subject: it is a fraction of the background recorded, a fraction of the object.
The give-away is always the same: the colour you are trying to delete appears inside the subject, not just around it.
- Glass and transparent plastics. The backdrop shows through the middle of the object. Key it hard and you get a milky rectangle of the old colour locked inside the bottle.
- Chiffon, tulle, net, lace. The weave covers part of each pixel and leaves gaps in the rest. Keyed one way the panel turns into a solid slab; keyed the other way it vanishes and takes the garment with it.
- Smoke, steam, flour, spray. There is no surface at all — the subject is a density. A threshold has to call the thin edge either present or absent, so the cloud becomes a hard-edged blob that still carries the old background colour.
- Thin hair, fur, feathers. Individual strands are narrower than a pixel, so each pixel is part hair and part whatever is behind it. This is the mildest version of the problem, and the easiest to live with.
- A cast shadow or a reflection. This one surprises people most, because the shadow is not a thing you photographed deliberately — but it is what stops the subject looking cut out.
Why moving the slider cannot fix it
It is worth being precise about this, because soft edges already exist and it is tempting to think the same control will stretch to cover it. It will not.
- Edge softness produces fractions in a band a few pixels wide, sitting on the boundary between subject and background. That is a transition, and it is doing exactly what it should.
- A see-through subject needs fractions over a region hundreds of pixels wide, in the middle of the object, where there is no boundary at all.
- Lower tolerance and the object keeps the background colour it was hiding. Raise tolerance and you start deleting the object itself. There is no position in between, because you are asking one number to describe two different quantities.
This site’s tool is a colour tool, and it will be honest about the limit: it will happily remove the backdrop around a glass object, and it has no way of knowing that the glass itself should end up sixty per cent opaque. For these subjects the removal is the first half of the job, not the whole of it.
What actually works
Four routes, in the order most people should consider them. The first three are real fixes; the fourth is the one that is usually right and almost never considered.
- Change the goal instead of the file. If the object only ever needs to sit on one background — a product page, a slide, a listing — composite it there and keep the original. A transparent PNG is only worth the trouble because it can go anywhere; if it is going one place, you have been paying for a freedom you are not using.
- Rebuild the see-through part by hand. Remove the background around the object first, then mask the object and set its opacity as a whole, or paint the coverage back in. It is slow per image and correct, which is why it is the standard answer for a hero shot and a bad answer for forty of them.
- Split the object into two layers. The solid part and the see-through part almost never need the same value. Cut them apart as two objects and give the second one its own opacity. A bottle becomes the glass shell plus the label; a veil becomes the folds plus the open panels.
- Two-background capture, if you still have the object. Shoot it twice against two clearly different backing colours, or composite it over two, and the pair of results tells you how much of each pixel is object and how much is background. This is the only route that recovers the real number rather than an estimate, and it has to happen before the object leaves your hands.
The ten-second test
Two checks, both free, both worth doing before you spend time on a cut-out that colour alone cannot finish.
- Look for your background colour inside the subject’s outline. If it is there, you have a see-through subject and the ordinary procedure will not complete.
- Put the result on black, then on white. Black shows what is still carrying the old background; white shows what got deleted that should not have been. A see-through subject will fail one of the two no matter how the slider is set — and that failure is the diagnosis.
If both checks pass, the object is opaque and the ordinary path applies: nominate the colour, remove it, rebuild the edge, cap the spill, export a PNG. If the first check fails, you already know which section above you need, and you have saved yourself an afternoon of adjusting a control that was never going to reach the problem.
Questions
How do I make a background transparent?
Nominate the background colour, remove it, tidy the edge and export a PNG — as long as the subject is opaque. If any part of the subject is see-through, such as glass, chiffon or smoke, the background is visible through the subject and no single set of colour settings will produce a correct file; that needs the transparency rebuilt by hand or captured on two different backgrounds.
Why is there still a rectangle of the old background inside my object?
Because the background is showing through the object rather than sitting behind it. Every pixel inside that rectangle is a mixture of object and background, and the key can only call it one or the other. Set it to keep and the mixture stays; set it to delete and you lose the glass along with it.
Can a colour key handle glass or a veil?
Partly. It can remove the backdrop around the object correctly. It cannot decide how opaque the object itself should be, because that is not a colour question — the tool would have to know what the object is, and a colour tool only measures colour distance.
What about a shadow the subject casts on the backdrop?
A cast shadow is background that is slightly darker, so a key treats it as background and removes it. That is usually not what you want: the shadow is what makes a subject sit in the scene rather than float above it. Either keep the shadow deliberately as its own layer, or accept that you will need to add a new one after the cut-out.
Does a soft edge help with a see-through object?
Only at the outline. Edge softness spreads the transition over a few pixels at the boundary between object and background. A see-through object needs a fraction of coverage spread across its whole area, which is a different kind of value in a different part of the image.
Is it worth shooting the object twice?
For one important image, yes — it is the only method that recovers the real coverage instead of guessing it. Shoot the object against two clearly different colours and the difference between the two frames tells you how much of each pixel is object. It has to be done at the shoot; once the object is gone you are back to rebuilding by hand.
Can I do all of this in the browser?
The removal, yes — images opened here are processed on your own device and never uploaded. The opacity rebuild is ordinary layer work, so it happens wherever you edit images; the two are separate steps and this site only does the first one.
Open the green screen remover — free, no account, and it exports a PNG with a genuinely empty background at the size you loaded. If your subject turned out to be opaque after all and the edge is what looks wrong, the edge guide is a symptom-by-symptom lookup table. If the result looks right but the file is wrong, start with the format guide.